CN101656274B - Method for improving open circuit voltage of amorphous silicon thin film solar cell - Google Patents

Abstract

The invention discloses a method for improving open circuit voltage of an amorphous silicon thin film solar cell. The method comprises that: an N type layer, an intrinsic layer and a P type layer are grown in sequence on an opaque substrate by adopting plasma assisted chemical vapor deposition technology, wherein the P type layer is divided into a P layer and a P<+> layer; when the P layer is grown, the growing time of the P layer is prolonged for t seconds; after the growth of the P layer is completed, flow, temperature and glow power of hydrogen are not changed, the P layer is etched for t seconds by adopting a hydrogen plasma etching method, and the P<+> layer is grown; and after the cell is taken out from a reacting chamber, an ITO transparent electrode is grown by magnetron sputtering. The method has simple and easy treatment process, not only can effectively improve the open circuit voltage of the amorphous silicon thin film solar cell to obtain the amorphous silicon thin film solar cell with large area and high open circuit voltage, but also has the advantages of low cost and mass production.

Description

Method for Improving Open Circuit Voltage of Amorphous Silicon Thin Film Solar Cell

technical field

The invention relates to the technical field of thin-film solar cells in new energy sources, in particular to a method for increasing the open-circuit voltage of amorphous silicon thin-film solar cells.

Background technique

The lack of energy and the increasingly serious environmental pollution have promoted the rapid development of new renewable energy sources such as solar energy. Photovoltaic power generation is an effective way to comprehensively manage energy and environmental problems, so it is placed at the top of renewable energy by various countries and has developed rapidly. In the past 10 years, the output of solar cells has been increasing at a rate of more than 30% every year. Since 2004, the products have always been in short supply. It is expected to develop at the same speed in the next ten years. It will reach 4GW in 2010 and exceed 15GW in 2020. The European Photovoltaic Industry Association predicts that it will reach 40GW in 2020. The development and utilization of solar energy has become a strategic decision for the sustainable development of energy in all countries in the world. my country has also formulated a new energy and renewable energy development plan from 2000 to 2015, and proposed to reduce the production cost of solar cells by 15% by 2015, so as to provide solar photovoltaic The large-scale application of power generation systems creates a good market prospect.

The main types of solar cells are: monocrystalline silicon solar cells; amorphous silicon solar cells; dye-sensitized solar cells; copper indium tin/copper indium gallium tin solar cells; chromium telluride solar cells, etc. Among them, monocrystalline silicon solar cells and amorphous silicon solar cells dominate. Other types of solar cells occupy a secondary position due to the constraints of shortage of raw materials, toxicity and other factors. Monocrystalline silicon solar cells started relatively early and have relatively high efficiency, but their cost is relatively high; amorphous silicon solar cells started relatively late, but their cost is relatively low, and they have developed rapidly recently.

Research progress at home and abroad: the first amorphous silicon solar cell made by RCA laboratory in 1976, the conversion efficiency was less than 1%; the amorphous silicon Schottky barrier cell made by Calson in 1977, the conversion efficiency was 5.5% %; In 1978, Daiban University in Japan developed an amorphous silicon PIN battery with a conversion efficiency of 4.5%; in 1981, the conversion efficiency of a-SiC:H/a-Si:H PIN batteries made by Japan’s Daiban University broke through 8%; The conversion efficiency of crystalline silicon cells reaches 12%. In 2006, the best three-junction stack in the world has achieved 15.07%; currently, the highest initial efficiency of the triple-junction stack is 15.3%.

The main advantage of amorphous silicon solar cells is low cost, because: silicon is abundant on the earth, and the material is non-toxic; the absorption coefficient of amorphous silicon thin films for visible light (the strongest part of the solar spectrum) is 1 to 2 orders of magnitude higher than that of crystalline silicon ;Amorphous silicon-based thin-film battery adopts low-temperature process (200°C), which not only saves energy consumption, but also facilitates the use of cheap substrates such as glass, stainless steel, and plastic; A laminated structure facilitates the realization of large-area, fully automated continuous production.

Amorphous silicon solar cells still have the problems of low conversion efficiency and low stability, but due to its low cost, non-toxicity, and easy mass production, it has developed rapidly.

The main performance parameters that characterize amorphous silicon solar cells are: open circuit voltage, short circuit current, fill factor, conversion efficiency, etc. In the research of silicon-based thin-film batteries, it has always been a research hotspot to improve the open-circuit voltage of the battery by changing the structure and composition of the P-type layer. High voltage solar cells have many special applications, such as solar cell phone rechargeable batteries. It is generally believed that the determinants of the open circuit voltage are the built-in potential and the band gap. Therefore, there are two main ways to increase the open circuit voltage. One is to adjust the difference between the Fermi levels of the P layer and the N layer, that is, the built-in potential, by adjusting the doping concentration of the P layer or the N layer; the other is to change the bandgap width of the intrinsic layer. However, many new problems will be encountered in actual operation, and the cost of the battery will be increased. Therefore, it is of great practical significance to propose a simple method for increasing the open-circuit voltage of amorphous silicon thin-film solar cells in the patented technology.

Contents of the invention

(1) Technical problems to be solved

In view of this, the main purpose of the present invention is to provide a method for increasing the open circuit voltage of the amorphous silicon thin film solar cell, so as to effectively increase the open circuit voltage of the amorphous silicon thin film solar cell.

(2) Technical solutions

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A method for increasing the open circuit voltage of an amorphous silicon thin film solar cell, the method comprising:

On an opaque substrate, an N-type layer, an intrinsic layer and a P-type layer are sequentially grown by plasma-assisted chemical vapor deposition technology, wherein the P-type layer is further divided into a P layer and a P ⁺ layer;

When growing the P layer, prolong the growth time of the P layer for t seconds. After the P layer is grown, keep the hydrogen flow rate, temperature and glow power constant, and use the hydrogen plasma etching method to etch the P layer for t seconds. Then grow the P ⁺ layer to form an amorphous silicon thin film solar cell; the t second is 90 seconds;

After the amorphous silicon thin-film solar cell is taken out from the reaction chamber, ITO transparent electrodes are grown by magnetron sputtering.

In the step of sequentially growing an N-type layer, an intrinsic layer, and a P-type layer by using plasma-assisted chemical vapor deposition technology, the growth of the N-type layer specifically includes: before depositing the N-type layer, cleaning the substrate surface 10 with hydrogen plasma seconds; when depositing N-type layer, hydrogen dilution ratio H ₂ /SiH ₄ is 10-20; doping ratio PH ₃ /SiH ₄ is 1:40-1:60; reaction pressure is 100Pa-300Pa; power density is 0.05 W/cm ² ~0.2W/cm ² ; the substrate temperature is 200°C~300°C; the reaction time is 5min~10min.

In the step of sequentially growing an N-type layer, an intrinsic layer and a P-type layer by using plasma-assisted chemical vapor deposition technology, growing the intrinsic layer specifically includes: when depositing the intrinsic layer, the hydrogen dilution ratio H ₂ /SiH ₄ is 3 ～10; reaction pressure 50Pa～150Pa; power density 0.03W/cm ² ～0.06W/cm ² ; substrate temperature 100℃～200℃; reaction time 40min～80min.

In the step of sequentially growing an N-type layer, an intrinsic layer, and a P-type layer by using plasma-assisted chemical vapor deposition technology, growing the P-type layer specifically includes: before depositing the P-type layer, using hydrogen plasma to grow the N-type layer The opaque substrate of the layer and the intrinsic layer is treated for 1 minute; when depositing the P-type layer, the hydrogen dilution ratio H ₂ /SiH ₄ is 90-120; the doping ratio B ₂ H ₆ /SiH ₄ is 1:20-1:80 The reaction pressure is 400Pa～600Pa; the power density is 0.5W/cm ² ～1.5W/cm ² ; the substrate temperature is 50℃～150℃; P ⁺ layer, first deposit the P layer, the growth time is 90 seconds longer than the actual required time, then, under the condition of constant hydrogen flow, temperature and glow power, use hydrogen plasma to etch for 90 seconds, and then grow P ⁺ layers.

The opaque substrate is a stainless steel substrate.

(3) Beneficial effects

As can be seen from the foregoing technical solutions, the present invention has the following beneficial effects:

1. The method for improving the open circuit voltage of amorphous silicon thin film solar cells proposed by the present invention adopts a plasma-assisted chemical vapor deposition system. The amorphous silicon thin-film solar cell with large area and high opening voltage has the advantages of low cost and large-scale production.

2. The method for improving the open-circuit voltage of amorphous silicon thin-film solar cells proposed by the present invention uses hydrogen plasma treatment on the P layer to successfully increase the open-circuit voltage of the battery by 25.7 millivolts, and the fill factor is increased by 0.039. The efficiency increased by about 9%. Under another experimental condition, the open circuit voltage reached 0.99 volts. Compared with the traditional method of adjusting the difference between the Fermi levels of the P layer and the N layer (that is, the built-in potential) and changing the bandgap width of the intrinsic layer by adjusting the doping concentration of the P layer or the N layer, it has low cost, The invention has the advantages of convenient precise control, simple method, wide application, cleanness and environmental protection, good portability and the like. Treating the P layer with hydrogen plasma can easily improve the open circuit voltage, fill factor and conversion efficiency of the cell.

3. The method for improving the open-circuit voltage of amorphous silicon thin-film solar cells proposed by the present invention can be applied to almost all amorphous silicon solar cells, microcrystalline silicon solar cells and various stacked solar cells, and is beneficial to the production of solar cells. It is of great significance to promote its use.

Description of drawings

Fig. 1 is the flow chart of the method for improving the open circuit voltage of amorphous silicon thin film solar cell provided by the present invention;

Figure 2 is a schematic diagram of the sequence of preparing the P-type layer of the battery according to an embodiment of the present invention; wherein, (1) is that the growth of the P layer is extended for 90 seconds, (2) is the etching of the P layer with hydrogen plasma for 90 seconds, and (3) is the subsequent growth P ⁺ layer;

Fig. 3 is the I-V curve of the battery prepared according to the embodiment of the present invention and the battery prepared without hydrogen plasma treatment of the P layer (others are identical) in the same experiment;

Figure 4 is the I-V curve of the battery prepared under another intrinsic layer condition by treating the P layer with hydrogen plasma, and its highest open circuit voltage can reach 0.99 volts.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

因此电池的开路电压得到提高。而且填充因子FF与J₀之间在串联电阻可以忽略的情况下也存在类似的关系：

在J_SC不变的时候，J_O的减小必然导致V_0C和FF的增大，从而提高电池的效率。再次，因为P层是纳米硅层，即纳米尺寸的晶粒镶嵌在非晶的母体中，由于晶粒比较致密，非晶母体比较疏松，因此在氢等离子体的作用下，非晶成分刻蚀较快，晶粒刻蚀较慢，经过一段时间的氢等离子体处理，P层的晶相比提高了，由于量子限制效应，带隙也变宽了，我们得到了高晶化率，宽带隙的掺杂纳米硅P层。P层带隙展宽导致N层与P层的费米能级差加大，即电池的内建电势加大，因此电池的开路电压自然变大。最后，P层的晶化，导致后面的P⁺层晶化，因此P⁺层的透光性变好，使更多能量的光进入到电池内部的本征层，使电池的开路电压等性能参数得到提高。The realization principle of the present invention is as follows: the growth time of the P layer is extended by 90 seconds, under the conditions of constant hydrogen flow rate, constant temperature, and constant glow power, hydrogen plasma is used to etch for 90 seconds, and then the P ⁺ layer is grown , all other conditions remain unchanged. Treating the p-layer with hydrogen plasma has many advantages: the most direct is to reduce the thickness of the p-layer over a prolonged period of time. Secondly, the etching of high-power hydrogen plasma greatly reduces the dangling bonds and some unstable weak bonds in the surface layer of the P layer, and the resulting density of band tail states and defect states is also reduced accordingly. Therefore, The recombination of carriers through the band tail and defects is greatly weakened, and the leakage current of the battery is relatively small. According to the ideal diode model of the solar cell, the relationship between the opening voltage and the reverse saturation current J ₀ is:

Therefore, the open circuit voltage of the battery is increased. And there is a similar relationship between the fill factor FF and J ₀ in the case of negligible series resistance:

When J _SC remains unchanged, the reduction of J _O will inevitably lead to the increase of V _0C and FF, thereby improving the efficiency of the battery. Again, because the P layer is a nano-silicon layer, that is, nano-sized grains are embedded in the amorphous matrix. Since the grains are relatively dense and the amorphous matrix is relatively loose, the amorphous components are etched under the action of hydrogen plasma. Faster, the grain etching is slower, after a period of hydrogen plasma treatment, the crystal ratio of the P layer is improved, due to the quantum confinement effect, the band gap is also widened, we have a high crystallization rate, a wide band gap Doped nano-silicon P layer. The widening of the bandgap of the P layer leads to an increase in the Fermi level difference between the N layer and the P layer, that is, the built-in potential of the battery increases, so the open circuit voltage of the battery naturally increases. Finally, the crystallization of the P layer leads to the crystallization of the subsequent P ⁺ layer, so the light transmission of the P ⁺ layer becomes better, allowing more energy of light to enter the intrinsic layer inside the battery, improving the performance of the battery such as open circuit voltage. parameters are improved.

Based on the above realization principle, as shown in Figure 1, Figure 1 is a flow chart of a method for improving the open circuit voltage of an amorphous silicon thin film solar cell provided by the present invention, the method specifically includes the following steps:

Step 101: On an opaque substrate, an N-type layer, an intrinsic layer and a P-type layer are sequentially grown by plasma-assisted chemical vapor deposition technology, wherein the P-type layer is further divided into a P layer and a P ⁺ layer;

Step 102: When growing the P layer, prolong the growth time of the P layer by t seconds, and after the P layer is grown, keep the hydrogen gas flow rate, temperature and glow power constant, and use the hydrogen plasma etching method to etch the P layer t seconds, then grow the P ⁺ layer;

Step 103: After the battery is taken out from the reaction chamber, ITO transparent electrodes are grown by magnetron sputtering.

With reference to Fig. 2, the specific growth process of the present invention is introduced in detail below:

1) The equipment used for growth is a plasma-assisted chemical vapor deposition system (PECVD), including reaction chambers (mounting chamber, doping chamber and intrinsic chamber), vacuum system, substrate heating and temperature control system, gas path control system etc.

2) Use high-purity silane with a concentration of 100% and hydrogen produced by a hydrogen generator as the reaction gas, and use borane with a purity of 0.5% and phosphine (diluted with hydrogen) with a purity of 1% as the doping gas.

3) The background vacuum of the sample chamber is 1×10 ^-4 Pa, and the frequency of the radio frequency power source for exciting the plasma is 13.56 MHz.

4) In order to reduce the impact of the deposits on the inner wall of the chamber on the deposited film, before each deposition, it was covered with the plasma under the same conditions as this deposition for 10 minutes.

5) Deposit the N layer first. Before deposition, clean the substrate surface with hydrogen plasma for 10 seconds; when depositing the N layer, the hydrogen dilution ratio (H ₂ /SiH ₄ ) is 10-20; the doping ratio (PH ₃ /SiH ₄ ) is 1:40 ～1:60; reaction pressure 100Pa～300Pa; power density 0.05W/cm ² ～0.2W/cm ² ; substrate temperature 200℃～300℃; reaction time 5min～10min.

6) Then deposit the intrinsic layer (ie layer I), the hydrogen dilution ratio (H ₂ /SiH ₄ ) is 3 to 10; the reaction pressure is 50Pa to 150Pa; the power density is 0.03W/cm ² to 0.06W/cm ² ; The substrate temperature is 100°C-200°C; the reaction time is 40min-80min.

7) Then deposit the P-type layer. Before deposition, treat with hydrogen plasma for 1 minute; when depositing P-type layer, hydrogen dilution ratio (H ₂ /SiH ₄ ) is 90-120; doping ratio (B ₂ H ₆ /SiH ₄ ) is 1:20- 1:80; reaction pressure is 400Pa～600Pa; power density is 0.5W/cm ² ～1.5W/cm ² ; substrate temperature is 50℃～150℃; reaction time is 3min～5min. Among them, the P-type layer is divided into P layer and P ⁺ layer. The P layer is deposited first, and the growth time is 90 seconds longer than the actual required time. Then, under the conditions of constant hydrogen flow rate, constant temperature, and constant glow power Next, hydrogen plasma was used to etch for 90 seconds, and then the P ⁺ layer was grown, and other conditions remained unchanged.

8) After the deposition is completed, the battery is taken out from the PECVD system, and the ITO transparent electrode is grown by magnetron sputtering.

According to the above growth process, referring to Figure 3 and Figure 4, the specific growth results are as follows:

An N-type layer, an I-layer, a P-type layer and an ITO transparent electrode are sequentially deposited on a stainless steel substrate to obtain a single-junction amorphous silicon solar cell. Use the solar simulator built by yourself to conduct I-V tests, and obtain the performance parameters of the battery: the average open circuit voltage is 0.905 volts, the average fill factor is 0.606, and the energy conversion efficiency is 5.5%; this method is not used in the same experiment (other conditions are exactly the same) Compared with the obtained battery, the open circuit voltage is increased by 25.7 millivolts, the fill factor is increased by 0.039, and the conversion efficiency is increased by about 9%.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (5)

1. a method that improves open circuit voltage of amorphous silicon thin film solar cell is characterized in that, this method comprises:

On opaque substrate, using plasma assistant chemical vapor deposition technology grow successively N type layer, intrinsic layer and P type layer, wherein, P type layer is divided into P layer and P again ⁺Layer;

When growth P layer, the growth time of P layer is prolonged t second, after the P layer growth finishes, keep hydrogen flowing quantity, temperature and glow power constant, adopt the hydrogen plasma lithographic method to P layer etching t second, P then grows ⁺Layer forms amorphous silicon thin-film solar cell; Described t second is 90 seconds;

After this amorphous silicon thin-film solar cell takes out from reative cell, with the magnetron sputtering ito transparent electrode of growing.

2. the method for raising open circuit voltage of amorphous silicon thin film solar cell according to claim 1, it is characterized in that, described using plasma assistant chemical vapor deposition technology is grown in the step of N type layer, intrinsic layer and P type layer successively, and growth N type layer specifically comprises:

Before the deposition N type layer, earlier with 10 seconds of hydrogen plasma clean substrate surface; During deposition N type layer, hydrogen thinner ratio H ₂/ SiH ₄Be 10～20; Doping ratio PH ₃/ SiH ₄It is 1: 40～1: 60; Reaction pressure is 100Pa～300Pa; Power density is 0.05W/cm ²～0.2W/cm ²Underlayer temperature is 200 ℃～300 ℃; Reaction time 5min～10min.

3. the method for raising open circuit voltage of amorphous silicon thin film solar cell according to claim 1, it is characterized in that, described using plasma assistant chemical vapor deposition technology is grown in the step of N type layer, intrinsic layer and P type layer successively, and the growth intrinsic layer specifically comprises:

During the deposition intrinsic layer, hydrogen thinner ratio H ₂/ SiH ₄Be 3～10; Reaction pressure is 50Pa～150Pa; Power density is 0.03W/cm ²～0.06W/cm ²Underlayer temperature is 100 ℃～200 ℃; Reaction time 40min～80min.

4. the method for raising open circuit voltage of amorphous silicon thin film solar cell according to claim 1, it is characterized in that, described using plasma assistant chemical vapor deposition technology is grown in the step of N type layer, intrinsic layer and P type layer successively, and the growing P-type layer specifically comprises:

Before the deposition P type layer, earlier with hydrogen plasma to the opaque substrate processing of grown N type layer and intrinsic layer 1 minute; During deposition P type layer, hydrogen thinner ratio H ₂/ SiH ₄Be 90～120; Doping ratio B ₂H ₆/ SiH ₄It is 1: 20～1: 80; Reaction pressure is 400Pa～600Pa; Power density is 0.5W/cm ²～1.5W/cm ²Underlayer temperature is 50 ℃～150 ℃; Reaction time 3min～5min.

5. the method for raising open circuit voltage of amorphous silicon thin film solar cell according to claim 1 is characterized in that, at the bottom of described opaque substrate is stainless steel lining.

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