CN102637781A - Method for preparing amorphous silicon thin-film solar battery with nip structure - Google Patents

Abstract

The invention discloses a method for preparing nip-structured silicon-based thin-film batteries using box-type plasma-enhanced chemical vapor deposition equipment, relates to the field of vacuum coating methods, and mainly solves the problem of inability to thoroughly wash doping elements in the technical method for preparing nip-structured batteries Phosphorus causes the problem that the residual phosphorus element affects the intrinsic i layer. A method for preparing an amorphous silicon thin-film solar cell with a nip structure, characterized in that three adjacent excitation electrodes are used as a group, the middle excitation electrode is used to sequentially prepare n, i, p layers, and the n layer is prepared After the end, the excitation electrode stops working, and the two adjacent excitation electrodes turn on the radio frequency signal to generate a plasma field to start cleaning the plasma box. After cleaning, the excitation electrode in the middle resumes work, and deposits i and p layers in sequence. The method has the advantages of simple steps, low implementation cost, little pollution degree of the intrinsic i layer, and can be widely used in the preparation of nip structure batteries.

Description

A kind of method for preparing nip structure amorphous silicon thin film solar cell

technical field

The invention belongs to the field of vacuum coating equipment and methods, and mainly relates to a method for preparing an amorphous silicon thin-film solar cell with a nip structure by a plasma-enhanced chemical vapor deposition method.

Background technique

A major disadvantage of amorphous silicon thin film cells is light-induced attenuation (S-W effect). One way to suppress light-induced attenuation is to reduce the thickness of the intrinsic layer, which leads to the concept of "multi-junction", whereby the thickness of the absorber layer of each sub-cell can be reduced by stacking several cells together. If materials with different energy bands are used for the absorbing layer of each sub-cell, the solar spectrum can be absorbed more fully, thereby improving the efficiency of the entire cell. For the absorbing layer with narrow band gap, μc-Si:H or a-SiGe:H are ideal materials, which have been widely used in practice.

The industrially popular multi-junction photovoltaic devices based on thin-film silicon are mainly a-Si:H/μc-Si:H double-junction cells, which have a serious disadvantage. Because nanocrystalline silicon has an indirect optical bandgap, a rather thick intrinsic i-layer of nanocrystalline silicon, such as 2000 nm, is required in the double junction in order to generate a large amount of photocurrent. However, the growth rate of nanocrystalline silicon that meets the device performance requirements is very slow (such as 9 nanometers per minute), and uniform large-area deposition also requires very large and complex production equipment, which is expensive and increases production costs. Reducing the thickness of the nanocrystalline Si i-layer film or shortening its deposition time renders the a-Si/nc-Si double-junction photovoltaic device no advantage over other designs. For a-Si:H and a-SiGe:H batteries, the requirements for equipment are not too high, and a-Si:H/a-SiGe:H/a-SiGe:H triple-junction batteries are currently the most advanced in the world. an important direction of development. At present, among the mass-produced multi-junction silicon-based thin-film cells, the highest efficiency is a-Si:H/a-SiGe:H/a-SiGe:H triple-junction cells, and the conversion efficiency after stabilization has exceeded 13%.

Plasma chemical vapor deposition equipment is referred to as PECVD equipment for short. Figure 1 and Figure 2 are schematic diagrams of cheap box-type plasma chemical vapor deposition equipment in the silicon thin film industry in recent years. At its heart is a movable plasma chamber that allows simultaneous and continuous deposition of all undoped and doped silicon films for photoelectric conversion devices on a large number of substrates in a single plasma reactor in a single vacuum chamber. As shown in Figure 1, the plasma box 2 is composed of a plurality of excitation electrodes 20A, 20B, 20C and a plurality of ground electrodes 21A, 21B, 21C, 21D, wherein the ground electrodes 21A, 21D on both sides are also used as side wall plates of the plasma box . All planar excitation electrodes and ground electrodes are assembled parallel to each other and kept equidistant. Excitation and ground electrodes were placed alternately, each sandwiched between two electrodes of opposite polarity with a spacing of 24 mm. Except that the sidewall ground electrode can only place a substrate on its inner surface, the two flat surfaces of all other electrodes can place the substrate 8 used for coating, usually a glass substrate. During the coating process, a glow discharge is generated in the region 7 between two adjacent electrodes, forming a plasma field. The number of excitation electrodes in the plasma box 2 can be any integer according to system design requirements, usually 12 or 18, and here only three are enough to illustrate the specific process of the present invention. The excitation electrodes 20A, 20B, 20C are isolated from the rest of the plasma chamber by insulators Teflon 6A and 6B. A shielded cable 12 is used to connect the excitation electrodes to an RF power source 13 outside the vacuum chamber 1 . The gas box (gas distribution plate, nozzle) 3 on the top of the plasma box 2 is placed above all the electrodes, and the gas raw materials are evenly and dispersedly introduced into the area 7 between adjacent electrodes through small holes 5 with a diameter of 1-2 mm. The two front and rear doors 15A and 15B of the plasma box are placed vertically at the two ends of the electrode arrangement, as shown in Figure 2, to limit the flow direction of the introduced gas in the plasma region from top to bottom, and not in the horizontal direction. direction out of the plasma chamber. The gas inlet 4 on the upper part of the vacuum chamber 1 is a metal hose. When the gas inlet valve 30A is opened, the source gas mixture, such as silane (SiH ₄ ), hydrogen (H ₂ ) and germane (GeH ₄ ), is drawn from the outside of the vacuum chamber. The gas pipeline is introduced into the gas box 3, and then flows down from the many pores 5 at the bottom of the gas box, flows along the gap area 7, and flows out from the hollow part 10 of the base structure 9 to between the plasma box 2 and the inner wall of the vacuum chamber 1 in the space, and is discharged from the vacuum chamber through the gas outlet 14 under the state that the gas outlet valve 30B is opened. Electric heaters are attached to the wall of the vacuum chamber 1 to increase or maintain the temperature of the entire vacuum chamber 1 and the plasma box 2 . 11 is the roller that the plasma box enters and exits the vacuum chamber 1.

Compared with other types of PECVD equipment, "box type" PECVD equipment has the advantages of low cost, large capacity and high gas utilization rate, and the prepared amorphous silicon thin film battery is cost-effective. However, just like other single-chamber PECVD equipment, although it can produce pin-structure amorphous silicon thin-film solar cells with excellent performance, it cannot produce nip-structure amorphous silicon thin-film solar cells with normal performance. The reason is that the conductivity type of the intrinsic layer of amorphous silicon grown in situ is weakly n-type. When preparing a cell with a pin structure, most of the doping element boron in the p layer can be washed away with an inert gas such as argon, and the remaining A very small amount of parts can properly neutralize the intrinsic i layer and improve the performance of the battery. This has been confirmed in the amorphous silicon industry, and even some laboratories deliberately doped the intrinsic i layer boron element; and when preparing a battery with nip structure, although the doping element phosphorus in the n layer can be washed away to a large extent after a long period of cleaning, the remaining very small part will still affect the intrinsic i layer. Have a significant impact and directly affect the performance of the battery.

Contents of the invention

In order to solve the technical method of using single-chamber PECVD equipment to prepare nip structure batteries in the background technology, because the doping element phosphorus cannot be thoroughly washed, the residual phosphorus element has a significant impact on the intrinsic i layer and directly affects the performance of the battery. The invention aims to provide a battery preparation method capable of reducing the pollution of the n-layer doping element phosphorus to the intrinsic i-layer when a single-cavity plasma chemical vapor deposition equipment is used to prepare a nip structure battery.

In order to achieve the above object, the present invention adopts the following technical means: a method for preparing a nip structure amorphous silicon thin film solar cell, its scheme is: adopt box-type PECVD equipment, use silane, germane and hydrogen in the preparation process Source mixed gas, the air pressure in the vacuum chamber is maintained between 300mT-1000mT, the substrate is placed on the surface of the parallel plate electrode, and the temperature of the substrate is maintained between 160-220°C. It is characterized in that: a box-type plasma chemical vapor deposition equipment is used to prepare an amorphous silicon thin film battery with a nip structure, and the substrate can be glass, or a flexible substrate including a stainless steel substrate or a polymer substrate, and the nip structure is prepared In the case of a battery, three adjacent excitation electrodes are used as a group in the plasma box, and the middle excitation electrode is used to prepare n, i, and p layers in sequence. After the preparation of the n layer, the excitation electrode stops working and the entire The reactive gas in the vacuum chamber, including the plasma box, is replaced by a gas with an etching function and the vacuum chamber is in a closed state, while the two adjacent excitation electrodes turn on the radio frequency signal to generate a plasma field and start to impact the plasma box. Clean up. In the closed state, the etching gas is dynamically circulated to etch away the P adsorbed on the surfaces of the plasma box and the cavity, and the surface of the n-layer has a large Si-Si bond energy and a tight combination, so it is not suitable for the Si-Si network. P plays a very good protective role. After cleaning, the two adjacent excitation electrodes stop working, the cleaning gas is discharged from the cavity, the reaction gas is introduced, and the middle excitation electrode is resumed to work, and i and p layers are deposited in sequence to prepare a nip structure battery. For multi-junction cells, this cleaning needs to be repeated after each n-layer deposition.

Furthermore, the gas used for etching is hydrogen.

Beneficial effect:

a. The steps of the method adopted in the present invention are simple, and the "box type" PECVD equipment with the advantages of low cost, large production capacity and high gas utilization rate is used to prepare nip structure amorphous silicon thin film solar cells, and the realization cost is low.

b. The quantum efficiency (QE) test of the battery prepared by the cleaning method adopted in the present invention and the battery prepared by conventional Ar washing is compared, and the degree of contamination of the intrinsic i layer is very small.

c. The method adopted in the present invention eliminates the cross-contamination of the intrinsic i layer by impurity elements by performing plasma cleaning on the plasma chamber after the deposition of the n layer and before the deposition of the p and i layers, without affecting the already deposited n layer Damage occurs, and a nip structure battery with normal performance is prepared.

Description of drawings

Fig. 1 is a front view of box-type PECVD equipment.

Fig. 2 is a side view of box-type PECVD equipment.

Fig. 3 is a QE test quantum efficiency curve of a nip structure battery washed with Ar for 15 minutes.

Fig. 4 is a QE test quantum efficiency curve of a nip structure battery washed for 10 minutes by the method of the present invention.

Detailed ways

As shown in Figures 1 and 2, the present invention uses a box-type plasma chemical vapor deposition device to prepare an amorphous silicon thin film battery with a nip structure. For ease of description, here only a group of excitation electrodes 20A, 20B, 20C related to the present invention and ground electrodes 21A, 21B, 21C, 21D corresponding to the excitation electrodes are given. All substrates are made of glass or flexible materials, of which only two substrates between 20B and 21B, two substrates between 20B and 21C, a total of four substrates are used to prepare the battery, and the battery is plated on it. Al on the back electrode and ZnO:Al for trapping light, while other substrates are made of ordinary cheap glass to protect the metal electrode plate during plasma cleaning. When preparing the nip structure battery, the excitation electrode 20B starts to work, and an n-type amorphous silicon layer is deposited on the four substrates by a general process. After the deposition of the n-layer is completed, the excitation electrode 20B is turned off and the gas in the vacuum chamber is replaced by H ₂ , which has an etching function for Si and P, and the gas includes but is not limited to H ₂ . When the vacuum chamber reaches a certain air pressure such as 500mT, the valves 30A and 30B are closed to make the vacuum chamber completely in a closed state, and a radio frequency signal of low power such as 50W is passed to the excitation electrodes 20A and 20C. At this time, a large amount of active radicals H are generated in the plasma box 2. Because there is a certain temperature gradient inevitably in the vacuum chamber, the gas in the closed state will circulate dynamically, which makes the active radicals H therein turn the plasma box and The adsorbed P on each surface inside the cavity is etched away, and the n-layer surface has a good protection effect on the P under the Si-Si network due to the large Si-Si bond energy and tight combination. After cleaning for a sufficient time such as ten minutes, the excitation electrodes 20A and 20C stop working, and the vacuum chamber valve 30B is opened to discharge the gas. Then the reaction gas is introduced, the excitation electrode 20B starts to work, the i layer and the p layer are sequentially deposited according to the normal process conditions, and the electrode with nip structure is prepared.

As shown in Fig. 3 and Fig. 4, the quantum efficiency (QE) of the battery prepared by using the cleaning method of the present invention and the battery prepared by conventional flushing with Ar was tested. It can be seen that if Ar is used for conventional flushing, the cleaning effect is very poor, and the battery needs to be under reverse bias to have better photogenerated carriers. If the cleaning method of the present invention is adopted, the degree of deviation of the QE curve under no reverse bias and -2V reverse bias is very small, indicating that the cleaning effect is very good, and the degree of contamination of the intrinsic i layer is very small.

Claims (2)

1. method for preparing nip structure amorphous silicon thin-film solar cell; Its scheme is: adopt box-type PECVD equipment; In the preparation process, use the source mist that comprises silane, germane and hydrogen; Air pressure in the vacuum chamber maintains between 300mT-1000mT, substrate is placed the surface of parallel plate electrode, and the temperature of substrate remains between 160-220 ℃; It is characterized in that: on substrate, prepare non-crystal silicon solar cell; In the plasma case with three adjacent exciting electrodes as one group; That middle exciting electrode is used for preparing successively n, i, p layer, after the preparation of n layer finishes this exciting electrode quit work and with whole vacuum cavity in comprise that the reacting gas in the plasma case is replaced into the gas with etching function and makes vacuum cavity be in closed state, and two other exciting electrode is opened radiofrequency signal and is produced plasma field and begin article on plasma body case and clean; Cleaning these two exciting electrodes that finish the next door, back quits work; The gas that cleans usefulness is discharged cavity, feed reacting gas, and the exciting electrode of centre is resumed work; Deposit i, p layer successively, preparation nip structure battery; For multijunction cell, after finishing, each n layer deposition all need repeat this cleaning.

2. according to the said a kind of method for preparing nip structure amorphous silicon thin-film solar cell of claim 1, it is characterized in that: said gas with etching function is hydrogen.

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