KR20150052759A - Improving quantum dot solar cell performance with a metal salt treatment - Google Patents

Abstract

A method of improving the performance of a quantum dot photovoltaic cell by metal salt treatment and a quantum dot photovoltaic cell are disclosed. The disclosed method comprises depositing a quantum dot film on a substrate layer of a photovoltaic cell, repairing defects in the quantum dot film by depositing the quantum dot film and then treating the quantum dot film with a salt solution, And performing a ligand exchange.

Description

TECHNICAL FIELD The present invention relates to a method for improving the performance of a quantum dot photovoltaic cell by metal salt treatment and a photovoltaic cell.

More particularly, to a photovoltaic cell comprising a quantum dots treated with a salt to enhance power conversion efficiency.

Photovoltaic (PV) cells convert light energy incident on a light-absorbing layer in a photovoltaic cell into current and voltage. A single photovoltaic cell comprising a light absorbing layer of silicon material has an open-circuit output voltage of about 0.5 to 0.7 volts and a surface area used for absorption of incident light, Temperature and other factors related to the output current (output current). Two or more photovoltaic cells are electrically connected to each other to form a photovoltaic module (PV module) having a higher output voltage and a higher output current than a single photovoltaic cell.

For example, photovoltaic cells are electrically connected in series and parallel to form a photovoltaic module with a power output of about 40 watts in a mechanical support structure having a thickness of about 25 inches, 20 inches wide, and 2 inches can do. The photovoltaic module may include other layers for protecting the photovoltaic cells in the module from exposure to contaminants, moisture, and mechanical stresses, and the photovoltaic module may comprise a photovoltaic module for connecting the photovoltaic module to another photovoltaic module or to an electrical load And may include electrical terminals.

Silicon used in the production of photovoltaic modules can be processed at high processing temperatures to refine and anneal raw materials and wafers. In recent years, alternative photovoltaic technologies have been studied that allow for lower processing temperatures, energy savings during cell fabrication, and the use of materials that can not with low cost fabrication processes and high process temperatures. For example, a photovoltaic cell with a light absorbing layer comprising a number of small colloidal semiconductor quantum dots (QDs) may be fabricated from silicon wafers sliced from silicon boules or ribbons The manufacturing cost can be remarkably reduced as compared with the photovoltaic cell. The quantum dots are formed by a wet chemical process in which spherical nanoparticles of light absorbing compounds such as lead sulfide (PbS) or other semiconductor compounds are synthesized in a liquid solution and then deposited as a granular film on a solid surface . Quantum dot synthesis and deposition can be performed at a temperature much lower than the temperature for producing silicon wafers, i.e., at room temperature or near room temperature.

The bandgap energy of the quantum dot is related to the size of the quantum dot. The size of the quantum dots can be expressed by a linear dimension of the quantum dots, for example, the diameter of the quantum dots. Each quantum dot in a photovoltaic quantum dot film can have a diameter of several nanometers to tens of nanometers. The power conversion efficiency of a photovoltaic cell can be maximized by adjusting the size of quantum dots forming a light absorbing layer in a photovoltaic cell at a selected wavelength of incident light.

Long-chain ligands extending from the surface of the quantum dots can serve as an insulator to reduce the mobility of charge carriers between the quantum dots in the photoabsorption layer of the photovoltaic cell. Thus, long chain ligands conjugated to the quantum dots reduce the power conversion efficiency of the photovoltaic cell. At this time, the power conversion efficiency η _p can be defined as a product of an open-circuit voltage V _oc , a short-circuit current J _sc, and a fill factor FF as shown in Equation (1).

[Equation 1]

η _p = V _oc x J _sc x FF

Here, the charge rate can be defined as a ratio of the maximum power of the photovoltaic cell to the product of V _oc and J _sc , as in Equation (2).

&Quot; (2) "

FF = (I _mp x V _mp ) / (V _oc x J _sc )

Here, I _mp means the output current when the output power of the photocell is the maximum, and V _mp means the output voltage when the output power of the photocell is the maximum.

 By replacing the ligands of the long chain with short ligands, the power conversion efficiency of the photovoltaic cells having quantum dots in the light absorption layer can be improved. To change the ligands of the long chain to shorter ligands throughout the material contained within each quantum dot, ligand replacement can be repeatedly performed during synthesis of the quantum dots or during deposition. Such ligand replacement can affect the electrical parameters of the device including the quantum dots by reducing the volume of the quantum dots and can also cause defects that interfere with the power conversion or current flow between the quantum dots in the QD film have. Examples of defects in the quantum dots include, but are not limited to, variations in the crystal structure of the quantum dots, volume or voids of the quantum dots or quantum dot films, cracks or other interruptions, a change in the spacing between atoms or functional groups in a crystal lattice (for example, the distance between the lead atoms and the sulfide group functional groups at different positions within one quantum dot) A change in distance or a change in distance from one quantum dot to another quantum dot).

Performing the ligand replacement during the quantum dot deposition process can increase uncertainty in parameters related to the performance of the finished photovoltaic cell, lengthening the fabrication time, and increasing the manufacturing cost of the photovoltaic cell. And defects in the quantum dots can degrade one or more of the I _mp , V _mp , and FF parameters and reduce the power conversion efficiency and the amount of output power from the photovoltaic cell. If the defects in the quantum dots are repaired after the quantum dots are deposited on the substrate, the photovoltaic cell can be fabricated at a lower cost than previously known methods for obtaining the specified power conversion efficiency.

The disclosed embodiments provide a method and an improved photovoltaic cell for improving the performance of a photovoltaic cell by repairing defects in the quantum dots.

In one aspect,

Depositing a quantum dot film on a substrate layer of a photovoltaic cell;

Depositing the quantum dot film, and then treating the quantum dot film with a salt solution to repair defects in the quantum dot film; And

And performing a ligand exchange on the quantum dot film. The present invention also provides a method for improving the performance of a photovoltaic cell.

The step of treating the quantum dot film with a salt solution may further include removing an excess salt solution in the quantum dot film. Another salt treatment step of the quantum dot film may be further included before deposition of the quantum dot film is completed and another quantum dot film is deposited. The step of treating the quantum dot film with a salt solution may be performed twice before another quantum dot film is deposited.

Depositing the quantum dot film until the quantum dot layer is formed into a predetermined thickness, treating the quantum dot layer with the salt solution, and performing the ligand replacement.

Repeating the steps of: depositing the quantum dot film until the photovoltaic cell achieves a predetermined minimum value of power conversion efficiency; treating the quantum dot layer with the salt solution; and performing the ligand replacement. Repeatedly performing the ligand replacement until the value of the shortcircuit current of the photovoltaic cell is equal to or greater than a predetermined minimum value of the shortcircuit current.

And forming the substrate layer with an N-type semiconductor material. Synthesizing the quantum dots from lead sulfide (PbS), and synthesizing the quantum dots from selenide lead (PbSe). Forming the substrate layer with zinc oxide or forming the substrate layer with titanium oxide.

The salt solution is prepared by mixing a solution of lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), rubidium chloride (RbCl), cesium chloride (CsCl), calcium chloride (CaCl2), ammonium chloride (NH4Cl), tetrabutylammonium chloride , Tetramethylammonium chloride (TMACl), potassium iodide (KI), rubidium iodide (RbI), cesium iodide (CsI), tetrabutylammonium iodide (TBAI), tetramethylammonium iodide (TMAI), potassium bromide From at least one salt compound selected from the group consisting of tetrabutylammonium (TBABr), tetramethylammonium bromide (TMABr) and ammonium fluoride (NH4F).

Before performing the ligand replacement, a step of covering the plurality of quantum dots with the salt solution may be further included. And performing the ligand replacement before covering the plurality of quantum dots with the salt solution.

In another aspect,

A first transparent outer layer;

A first electrode adjacent the first transparent outer layer;

A transparent semiconductor layer electrically connected to the first electrode;

A quantum dot layer comprising at least one quantum dot film modified by forming a P-N junction with the transparent semiconductor layer by washing at least one quantum dot film with a salt solution and ligand replacement;

A second outer layer; And

And an interface layer disposed between the second outer layer and the quantum dot layer.

In another aspect,

Synthesizing a solution of quantum dots stabilized by long chain ligands;

 Depositing a quantum dot film on the transparent semiconductor layer;

Repairing defects in the quantum dot film by a salt treatment of the quantum dot film; And

And performing ligand replacement on the quantum dot film,

Each of the two salt treatment processes may comprise:

Covering the quantum dot film with a salt solution for a predetermined period of time; And

And removing excess salt solution from the quantum dot film. ≪ IMAGE >

In another aspect,

Depositing a quantum dot film on a substrate layer of a photovoltaic cell;

Depositing the quantum dot film, and then treating the quantum dot film with a salt solution to repair defects in the quantum dot film;

Performing a ligand exchange on the quantum dot film; And

 And depositing a plurality of quantum dot films until a quantum dot layer having a predetermined thickness is formed,

 There is provided a photovoltaic cell produced by a process wherein twice the salt treatment and the ligand replacement are performed on each of the quantum dot films before the subsequent deposition of the quantum dot film.

According to the disclosed embodiments, the defect is improved by going through the salt treatment process of the quantum dot film, so that the performance of the photovoltaic cell is improved, and manufacturing cost and time are saved.

1 is a schematic view of a photovoltaic cell according to an embodiment.
2 is a block diagram illustrating the layers of the photovoltaic cell shown in FIG.
3 is a circuit diagram of a photovoltaic cell according to an embodiment.
4 is a schematic diagram of a photovoltaic module including a plurality of photovoltaic cells connected in series and in parallel.
Figure 5 is a side view schematically showing that the substrate layer of the photovoltaic cell is exposed to a solution comprising nanoparticles with long chain ligands extending from the surface in solution.
FIG. 6 is a side view of a quantum dot film deposited on a photovoltaic cell substrate, showing that the spacing between quantum dots is an example of defects that can reduce power conversion efficiency.
FIG. 7 is a view showing an example of a quantum dot film after some of the defects in the quantum dot film are removed by the first salt treatment process in FIG. 6. FIG.
FIG. 8 is a view showing an example of quantum dots after defects in a quantum dot film are removed more by the second salt treatment process in FIGS. 6 and 7. FIG.
Fig. 9 schematically shows a quantum dot film after processing of a quantum dot film for replacing a long chain ligand extending from each quantum dot with a short ligand in Fig. 6 to Fig. 8;
10 is a plan view showing an example in which a quantum dot layer including at least one quantum dot film having undergone two salt treatment steps and a ligand conversion step is provided between two adjacent layers in a photovoltaic cell.
11 is a graph showing the relationship between current density and voltage for alternative embodiments using different salt compounds for the salt treatment of the quantum dots.
FIG. 12 shows a comparison of the current and voltage output from the photovoltaic cell according to the embodiment in which the quantum dots before the ligand replacement are treated with the salt solution, and shows a comparison of the photovoltaic cells produced without exposing the salt solution.
13 is a flow chart illustrating an example of steps in a method embodiment.

Hereinafter, a method of improving the performance of a photovoltaic cell according to embodiments of the present invention and a quantum dot photovoltaic cell will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements, and the size and thickness of each element may be exaggerated for clarity of explanation.

The power conversion efficiency of a photovoltaic cell including a lead sulfide (PbS) quantum dot layer for light absorption can be improved by a salt treatment process for the quantum dot layer and a ligand replacement process. According to one embodiment, a quantum dot film may be deposited, followed by a salt treatment process and a ligand replacement process for the quantum dot film. The deposition process of the quantum dot film may be repeated until the quantum dot layer is formed to a desired thickness, and at least one salt treatment process and at least one ligand conversion process may be performed between each deposition process. One salt treatment process may include a step of covering the salt solution with the most recently deposited quantum dot film in the quantum dot layer and then a step of removing the excess salt solution. Among the embodiments, there may be an embodiment that includes exactly twice the salt treatment process for each quantum dot film. Yet another embodiment provides a photovoltaic cell comprising a light absorbing layer with quantum dot films that have undergone two salt treatment steps and ligand replacement after each quantum dot film has been deposited.

Halide ions in the salt solution can passivate lead (Pb) sites on the outer surface of the quantum dots in the quantum dot film. The alkali metal ions may passivate the surface chalcogen sites and / or repair lead (Pb) vacancies in the semiconductor crystal structure. Simultaneous inflow of cations and anions maintains the charge neutrality of the quantum dots. According to embodiments, the step of exposing the quantum dot films to a metal salt solution may include a step of replacing a ligand having a high probability that metal cations and halogen anions having small ion diameters reach the surface of the quantum dots to remove surface recombination sites May be performed prior to the process.

The devices according to the embodiments showed improved FF and J _sc as compared to the control devices manufactured by performing the ligand replacement without the salt treatment process. It has also been shown that the cross over between light and dark current-voltage characteristics is also reduced. A high temperature process is required for a process for producing a pn junction in a photovoltaic cell, for example, a melting, annealing or diffusion process of single crystal or polycrystalline silicon, a subsequent oxidation or diffusion process of silicon, The pn junction can also be formed at about room temperature (25?). Unlike conventional well-known photovoltaic cells made from silicon sliced from ingots or ribbons, according to this embodiment, a single photovoltaic cell of almost any size can be fabricated.

A photovoltaic cell according to one embodiment is schematically illustrated in FIG. Some layers in FIG. 1 may be exaggerated in thickness. Incident light 101 such as sunlight or artificial light is incident on the quantum dot layer 134 through the first outer layer 111 of the photovoltaic cell 100, the first electrode 110, the semiconductor layer 108, When absorbed, a potential difference is generated between the first electrode 110 and the second electrode 102. The interface layer 104 may separate the quantum dot layer 134 from the second electrode 102. In FIG. 1, the case where the photovoltaic cell 100 has a rectangular outer shape is illustrated by way of example, but the present invention is not limited thereto. According to alternative embodiments, the rectangular outer shape of the photovoltaic cell 100 may be replaced by a square, circular, semicircular, or irregular or other outer shape. The various layers in the photovoltaic cell 100 may be substantially planar as shown in Fig. 1, or alternatively may be formed as a curved surface to focus incident light on a light absorbing layer in the photovoltaic cell.

2 is a view showing an example of each layer of the photovoltaic cell 100 shown in FIG. The first outer layer 111 may serve to protect the other layers from moisture, dust, and other mechanical damage. Preferably, the first outer layer 111 has transparency in the frequency region of the incident light 101 that can be converted to electric power. Examples of materials that the first outer layer 111 includes include glass, polycarbonate, acrylic, and the like. This is an example only, and is by no means limiting. The first electrode 110 may be made of an optically transparent electrical conductor such as indium tin oxide (ITO). Light passing through the first electrode 110 is then incident on the semiconductor substrate layer 108, which is in electrical contact with the first electrode 110. The semiconductor substrate layer 108 may be made of a transparent N-type semiconductor material, such as titanium oxide or zinc oxide (ZnO). The first electrode 110 may operate as a cathode when the photovoltaic cell is electrically connected to other photovoltaic cells of the photovoltaic module.

A P-N junction of the semiconductor can be formed between the semiconductor substrate layer 108 and the light absorption layer 134 made of quantum dots deposited on the semiconductor substrate layer 108. [ Before the quantum dot layer 134 is deposited on the semiconductor substrate layer 108, the quantum dots may be synthesized in the liquid solution to a size corresponding to the desired energy band gap. The quantum dots can be stabilized in the quantum dot solution by long chain ligands extending from the quantum dots. Examples of ligands in the examples include ethanedithiol (EDT); 1,2-benzenedithiol (BDT); 1,3-benzenedithiol; 1,4-benzenedithiol; And mercaptopropionic acid (MPA). Other parameters such as, for example, the length, width and thickness of a quantum dot, or the size of a quantum dot, such as the diameter of a nearly spherical quantum dot, the number of quantum dots per unit area, and the bandgap of a quantum dot, have. After the quantum dots are deposited on the quantum dot film, the remaining quantum dot solution can be removed from the substrate and the quantum dot film by rotating the substrate. Alternatively, the substrate may be placed in a lead sulphide (PbS) solution and withdrawn to form a quantum dot film. It is preferred that the quantum dots deposited in the quantum dot film on the substrate have optical and electrical properties of the quantum dots in solution prior to the beginning of deposition. By depositing quantum dots having different energy bandgaps, a photovoltaic cell can be formed that is adapted to convert multiple wavelengths of incident light.

An interface layer 104, for example, a layer comprising at least one molybdenum oxide (MoO _x ) may be adjacent to the quantum dot layer 134. The second electrode 102, which is in electrical contact with the interface layer 104, may or may not include an array of conductors made of gold (Au). The second electrode 102 is arranged like a second outer layer of the photovoltaic cell 100 and can act as an anode.

3 is a circuit diagram showing one photovoltaic cell 100 according to one embodiment. 4 is a schematic diagram of a photovoltaic module 112 including a plurality of photovoltaic cells 100 connected in series 114 and parallel 116. 4, the photovoltaic module 112 can collect the output power of the individual photovoltaic cells 100 at the positive output terminal 118 and the negative output terminal 120. The photovoltaic module 112 may comprise mechanical support means for the interconnected photovoltaic cells 100. The photovoltaic module 112 may also prevent mechanical damage to the photovoltaic cells 100 and exposure to moisture, dust, and other contaminants. The outer glass layer 111 may correspond to the first outer layer 111 of the photovoltaic cell 100 shown in FIG. This outer glass layer 111 covers a plurality of photovoltaic cells 100 as shown in FIG. 4, and the number thus covered determines the number of photovoltaic cells 100 included in the photovoltaic module 112.

5 to 10 are diagrams illustrating a process of forming a quantum dot layer of the photovoltaic cell 100 from nanoparticles synthesized in a quantum dot solution. 5 to 10, at least one quantum dot film may be formed on the semiconductor substrate layer 108 by deposition of nanoparticles of a quantum dot solution. Also, a salt treatment and a ligand replacement process can be performed after deposition of each quantum dot film. Quantum dots can be synthesized from chalcogenide, such as lead sulphide (PbS) or lead selenide. According to the drawings, quantum dots 106 and long chain ligands 130 are shown exaggerated relative to the semiconductor substrate layer 108. This illustration is intended to emphasize the gap 107 (defect 107) between the quantum dots 106 in the granular QD film before and after the two salt treatment processes.

According to the example shown in FIG. 5, the semiconductor substrate layer 108 having the surface 109 on which the quantum dot film is deposited is deposited by a liquid quantum dot solution containing floating nanoparticles 105, for example, a lead sulfide solution One side is covered. Each spherical nanoparticle 105 represents a quantum dot 106 having an outwardly extending long chain ligand 130.

Synthesis of the nanoparticles is completed when the nanoparticles obtain a desired minimum average value for the diameter, e.g., the diameter corresponding to the desired bandgap. Alternately, the size of the quantum dot may correspond to a minimum, maximum or average value of another linear dimension of the quantum dot. The preferred size of the quantum dot 106 described above can be determined through experiments on the completed photovoltaic cell 100. [ For example, a maximum value of J _sc or a maximum value of? _P at a selected wavelength or intensity of incident light.

Figure 6 is an illustration of an example of a granular quantum dot film 135 comprising quantum dot 106 nanoparticles with long chain ligands 130. 6, the quantum dot film 135 deposited on the surface 109 of the silicon substrate layer 108 has a gap between the quantum dots 106 as the spacing between each quantum dot is irregular. , Defects 107 in the form of cracks or voids. Defect 107 and long chain ligand 130 may reduce the power conversion efficiency? _P of the photocell, which may be due to disturbing charge carrier movement. Some defects 107 may also be formed as a result of ligand replacement. Ligand replacement can shorten the insulating ligands between the quantum dots, but can also benefit from improving the power conversion efficiency of the photovoltaic cell by minimizing the number and degree of defects 107 described above.

After the deposition process of each quantum dot layer is completed, a metal ion process and a ligand conversion process can be performed. The metal ion process may involve covering the QD film with a salt solution and removing the excess salt solution from the QD solution. Thus, the metal ion process may be expressed as a salt treatment.

FIG. 7 is a view showing some defects 107 from the example shown in FIG. 6 repaired by the first salt treatment process 124A of the quantum dot film 135. FIG. Compared with FIG. 6, in FIG. 7, some defects 107 have been repaired by filling the gaps in the quantum dot film 135 with quantum dots 106. FIG. The first salt treatment step 124A can be performed after the QD synthesis in the solution is finished and the QD film 135 is deposited on the surface 109 of the substrate layer. A portion of the remaining salt solution can be removed by rotating the semiconductor substrate 108. The remaining salt solution may be removed by cleaning the quantum dot film 135 with a wash solution 128 such as methanol. The wash solution 128 and the salt solution may also be removed by rotation of the substrate 108 have. The above-mentioned methanol may be replaced by another polar solvent.

In some embodiments, more defects 107 in the quantum dot film 135 may be repaired by the second salt treatment process 124B, also illustrated in FIG. The second salt treatment process may be performed after the first salt treatment process 124A is performed, but before deposition of another quantum dot film is performed. Two separate salt treatment processes, each lasting for a predetermined time (e.g., 3 seconds), were more effective than one salt treatment process that lasted as long as possible. Moreover, a photovoltaic cell having a lead sulfide light absorbing layer as part of a P-N junction shows a significant improvement in power conversion efficiency over a single salt-treated photovoltaic cell after a two-step salt treatment process. According to certain embodiments, exactly two salt treatment processes can be performed to repair defects in each quantum dot film deposited within the photovoltaic quantum dot layer. The salt treatment process can be completed by removing the salt solution that remains in the quantum dot film.

The long chain ligands present on the outer surface of the quantum dots 106 can be shortened by exposing the quantum dots to the ligand replacement compound 126. Shortening the long chain ligand can increase the power conversion efficiency? _P. Unlike previously, salt exposure, washing, and ligand replacement can only be done after synthesis of the quantum dots.

FIG. 9 is a diagram schematically showing an embodiment after replacing a long chain ligand of each quantum dot with a short ligand in the quantum dot films shown in FIGS. 6 to 8. FIG. In the ligand replacement process shown in Figure 9, the quantum dot film 136 is covered with the ligand replacement compound 126 for a predetermined duration, and then the remaining ligand replacement compound is washed and, if possible, Can be removed. In the embodiment shown in FIG. 9, the quantum dots 106 do not have long chain ligands, but are in close contact with each other and have no gaps, cracks, or other defects that can interfere with the movement of the charge carriers of the photovoltaic cell 100 The ligand replacement can be done after the QD film is deposited and before another QD film is deposited. According to some embodiments, the ligand replacement process may be performed after the salt treatment process is performed. In general, the ligand replacement process may precede the salt treatment process. The ligand replacement process may be repeatedly performed until the photocell has a selected minimum value of the power conversion efficiency. Alternatively, the ligand replacement process may be repeated until the photocell short-circuit current is greater than or equal to the selected minimum value of the short-circuit current.

10 is a side view of the layers included in the photovoltaic cell according to the present embodiment. 10, the quantum dot layer 134 may have a predetermined thickness to obtain a desired value of power conversion efficiency η _p is the desired value or generally to the short-circuit current J _sc. The quantum dot layer 134 is also improved in defects for efficient charge carrier movement in the photovoltaic cell 100 and is in good electrical contact with the interface layer 104 and the semiconductor substrate layer 108.

In one embodiment, a layer of quantum dots may be spin casted onto the zinc oxide phase at 2000 RPM (revolutions per minute). The completed QDs are then covered with a salt solution (eg, a 0.025 M salt concentration in the solvent) applied onto the QD layer. After 3 seconds, the salt solution is removed by rotating the photocell, After washing with methanol to remove, two salt treatment steps are carried out. . Quantum dots are then treated with 1,3 benzenedithiol (BDT) to replace long chain oleic acid ligands with short BDT ligands. The ligand replacement solution can then be removed by washing. The combined processes of deposition, double salt treatment and ligand replacement can be repeated 12 times to achieve the desired performance of the photovoltaic cell.

The effect of the above-described salt treatment process can be further explained with reference to FIG. 9 and Table 1. FIG. Table 1 shows the power conversion efficiency of the photovoltaic cell according to the embodiment. For the results shown in the examples of Table 1 and FIG. 9, oleic acid was replaced with 1,3 benzenedithiol, but other ligand replacement compounds were used identically. Compared to the case without salt treatment under AM1.5G illumination, when the salt treatment process using rubidium chloride (RbCl) was performed, FF was improved 57%, J _sc was improved 48% and η _p was improved 74% . Also, when the salt treatment process using calcium chloride (CaCl ₂ ) was performed, the performance was improved, but it was lower than that using potassium chloride (KCl). In all cases of treatment with other salts including lithium chloride (LiCl), sodium chloride (NaCl), ammonium chloride (NH4Cl), potassium bromide (KBr) and potassium iodide (KI) The performance of the photovoltaic cell was improved compared with the case without the photovoltaic cell.

As shown in Table 1, the highest power conversion efficiency was measured using rubidium chloride. Alternative embodiments include use of other salts, treatment time, rotational speed, and application sequence of reagents. For example, alternative embodiments include lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), rubidium chloride (RbCl), cesium chloride (CsCl), calcium chloride (CaCl2), ammonium chloride (TBAI), tetramethylammonium iodide (TMAI), potassium bromide (TBAI), tetrabutylammonium iodide (TMAI), tetrabutylammonium iodide Preparing a salt solution for repairing a quantum dot film from at least one salt solution selected from the group of salt solutions consisting of KBr, tetrabutylammonium bromide (TBABr), tetramethylammonium bromide (TMABr) and ammonium fluoride (NH4F) Step < / RTI >

Figure 11 shows the photovoltaic performance curves for the different salts of TBACl (152), LiCl (154), NaCl (156), KCl (158), RbCl (160), and CsCl Fig. 12 is a graph comparing the photovoltaic cell performance when the quantum dot film is treated with calcium chloride (Cacl ₂ ; 142), when the salt is treated with potassium chloride (KCl), and when the salt treatment is not performed.

13 is a diagram illustrating an example of steps in a method embodiment. Referring to FIG. 13, the method according to the present embodiment may include a step 202 of synthesizing quantum dot particles in a solution. And depositing a quantum dot film on the surface of the semiconductor layer (204). Here, the semiconductor layer may be an N-type semiconductor layer. After deposition of the quantum dot film, the quantum dot film may undergo at least one salt treatment process. In other words, the method according to this embodiment may include the step 206 of covering the quantum dot film with a predetermined salt solution for a predetermined duration. Here, the salt solution may be appropriately selected from the group consisting of the above-mentioned salt solutions. The method according to this embodiment may include a step 208 of removing the remaining salt solution by selectively washing the quantum dot film after the step 206 of covering with the salt solution described above is made. The method according to the present embodiment may include a second salt treatment process 210, 212 performed after the first salt treatment process 206, 208 described above. The second salt treatment process 210, 212 may be terminated by washing the quantum dot film and removing 212 the remaining salt solution.

Also, the method according to the embodiment shown in FIG. 13 may include a ligand replacement process 214 after the salt treatment processes are performed. In an alternative embodiment, the ligand replacement process 214 may be performed earlier than any or all of the salt treatment processes. After the above-described ligand replacement step 214 is performed, the thickness of the quantum dot layer can be determined, and the thickness of the quantum dot layer can be compared with a preferable value of the thickness. If the thickness of the quantum dot layer comprising at least one quantum dot film is greater than or equal to a predetermined minimum thickness value, as shown in step 216, then the next layer of photovoltaic cell production proceeds as shown in step 220. If the quantum dot layer is smaller than the predetermined minimum thickness value, another quantum dot film is deposited on the previously deposited quantum dot film as shown in step 218, and then returns to step 206 to repeat the salt treatment process and the ligand replacement process do. Some of the steps may be performed in an order different from that shown in FIG. These variations may be considered to be within the scope of the disclosed embodiments.

While a number of embodiments have been described in detail above, they should be construed as examples of preferred embodiments rather than limiting the scope of the invention. Therefore, the scope of the present invention is not to be determined by the described embodiments but should be determined by the technical idea described in the claims.

100: photovoltaic cell
101: incident light
102: second electrode
104: interfacial layer
106: Qdot
108: semiconductor substrate layer
109: Surface of the semiconductor substrate layer
110: first electrode
111: first outer layer
130: long chain ligand
134: Quantum dot layer
135: granular quantum dot layer
124A: First salt treatment process
124B: Second salt treatment process
128: Cleaning solution

Claims (20)

Depositing a quantum dot film on a substrate layer of a photovoltaic cell;
Depositing the quantum dot film, and then treating the quantum dot film with a salt solution to repair defects in the quantum dot film; And
And performing a ligand exchange on the quantum dot film. The method according to claim 1,
Wherein the step of treating the quantum dot film with a salt solution further comprises removing an excess salt solution in the quantum dot film. The method according to claim 1,
Further comprising the step of treating the quantum dot film with another salt before the deposition of the quantum dot film is completed and another quantum dot film is deposited. The method according to claim 1,
Wherein treating the quantum dot film with a salt solution is performed twice before another quantum dot film is deposited. The method according to claim 1,
Repeating the steps of depositing the quantum dot film until the quantum dot layer is formed into a predetermined thickness, treating the quantum dot layer with the salt solution, and performing the ligand replacement. Way. The method according to claim 1,
Further comprising repeating the steps of depositing the quantum dot film until the photovoltaic cell achieves a predetermined minimum value of power conversion efficiency, treating the quantum dot layer with the salt solution, and performing the ligand replacement. How to improve performance. The method according to claim 1,
Repeatedly performing the ligand replacement until the value of the short circuit current of the photovoltaic cell is greater than or equal to a predetermined minimum value of the short circuit current. The method according to claim 1,
And forming the substrate layer from an N-type semiconductor material. The method according to claim 1,
And synthesizing the quantum dots from at least one of lead sulfide (PbS) and selenium telluride (PbSe). The method according to claim 1,
And forming the substrate layer with at least one of zinc oxide and titanium oxide. The method according to claim 1,
The salt solution is prepared by mixing a solution of lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), rubidium chloride (RbCl), cesium chloride (CsCl), calcium chloride (CaCl2), ammonium chloride (NH4Cl), tetrabutylammonium chloride , Tetramethylammonium chloride (TMACl), potassium iodide (KI), rubidium iodide (RbI), cesium iodide (CsI), tetrabutylammonium iodide (TBAI), tetramethylammonium iodide (TMAI), potassium bromide From at least one salt compound selected from the group consisting of tetrabutylammonium (TBABr), tetramethylammonium bromide (TMABr), and ammonium fluoride (NH4F). The method according to claim 1,
Further comprising the step of covering the plurality of quantum dots with the salt solution before performing the ligand replacement. The method according to claim 1,
And performing the ligand replacement before covering the plurality of quantum dots with the salt solution. A first transparent outer layer;
A first electrode adjacent the first transparent outer layer;
A transparent semiconductor layer electrically connected to the first electrode;
A quantum dot layer comprising at least one quantum dot film modified by forming a PN junction with the transparent semiconductor layer with at least one quantum dot film washed with a salt solution and ligand replacement;
A second outer layer; And
And an interface layer positioned between the second outer layer and the quantum dot layer. 15. The method of claim 14,
Wherein the quantum dot layer comprises a plurality of quantum dot films and each of the quantum dot films is modified by washing with a salt solution and by ligand replacement before another plurality of quantum dot films are deposited. 15. The method of claim 14,
Wherein the quantum dots are modified by ligand replacement until the photovoltaic cell has a predetermined minimum value of power conversion efficiency. 15. The method of claim 14,
Wherein the first electrode comprises indium tin oxide formed into a layer that is transparent to visible light. 15. The method of claim 14,
Wherein the photovoltaic cell has a power conversion efficiency of at least 4 percent. Synthesizing a solution of quantum dots stabilized by long chain ligands;
Depositing a quantum dot film on the transparent semiconductor layer;
Repairing defects in the quantum dot film by a salt treatment of the quantum dot film; And
And performing ligand replacement on the quantum dot film,
Each of the two salt treatment processes may comprise:
Covering the quantum dot film with a salt solution for a predetermined period of time; And
And removing excess salt solution from the quantum dot film. Depositing a quantum dot film on a substrate layer of a photovoltaic cell;
Depositing the quantum dot film, and then treating the quantum dot film with a salt solution to repair defects in the quantum dot film;
Performing a ligand exchange on the quantum dot film; And
And depositing a plurality of quantum dot films until a quantum dot layer having a predetermined thickness is formed,
Wherein the two quantum dot films are subjected to twice salt treatment and ligand replacement before the subsequent deposition of the quantum dot film.

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