Facile Optimization Method for the Passivation Layer Preparation in Silicon Heterojunction Solar Cell by Monitoring Its Growth Rate
Lei Zhao1,2, Guanghong Wang1, Hongwei Diao1, Wenjing Wang1,2
1Key Laboratory of Solar Thermal Energy and Photovoltaic System of Chinese Academy of Sciences, Institute of Electrical Engineering, the Chinese Academy of Sciences, Beijing, China
/2University of Chinese Academy of Sciences, Beijing, China

Recently, more and more photovoltaic practitioners paid much attention to the hydrogenated amorphous/crystalline silicon (a-Si:H/c-Si) heterojunction (SHJ) solar cells, due to its high efficiency achievable in practice and very simple fabrication process. A critical point to achieve high conversion efficiency for such cell is to insert an intrinsic a-Si:H thin layer between the doped a-Si:H layer and the c-Si wafer for passivating the a-Si:H/c-Si heterojunction interface. Thus the optimization of the passivation layer becomes one of the important steps during the fabrication of the high-performance SHJ solar cell. Plasma enhanced chemical vapor deposition (PECVD) is more usually used for the thin film silicon deposition due to its mature industrial application. In order to improve the passivation performance, various PECVD conditions, such as plasma frequency, substrate temperature, hydrogen dilution ratio, deposition pressure, deposition power, gas flow rate ratio of hydrogen to silane and so on, should be optimized carefully. People have to measure the effective minority carrier lifetime (τeff) of the passivated c-Si wafer directly, or characterize the microstructure of the passivation layer via Raman and Fourier transform infrared (FTIR) spectra, which is usually time-consuming and laborious. Here, PECVD was utilized to prepare the thin film silicon passivation layer via changing the deposition condition, such as substrate temperature, gas flux, plasma excitation power, and deposition pressure. By investigating the passivation performance and the growth rate of the passivation layer as functions of the above deposition parameters, a facile method was proposed to optimize the deposition condition for the passivation layer preparation. It is to monitor the growth rate R of the passivation layer and to calculate the second-order derivative of R with respect to the corresponding deposition parameter. When the second-order derivative of R presents an extremum, the corresponding value of the considered deposition parameter can be determined as its optimized choice.