Study Of Annealing And Passivation Process In High Efficiency Si-Organic Hybrid Solar Cells

Silicon-organic hybrid solar cells not only have the advantages of silicon solar cells in high photoelectric conversion efficiency,long service life and stable photovoltaic characteristics,but also have the superiority of organic solar cells in simple manufacturing process,and low costs.Silicon-organic hybrid solar cells have the potential to overcome the high costs and complicate procedures of silicon solar cells,and at the same time solve the problem of low carrier mobility in organic solar cells.Most of the silicon-organic hybrid solar cells have a heterojunction which consist of an n-type based silicon and a.PEDOT:PSS is a p-type organic polymer which is most commonly used in research works due to its advantages of high transmittance and high conductivity.Since 2010,the research of silicon-organic solar cells has been sprung up.Many remarkable progresses have been made in domestic and abroad.The record of photovoltaic conversion efficiency has been refreshed constantly.However,there are still some issues to be further studied,such as,how the characteristics of PEDOT:PSS film affect the photovoltaic performance,how the passivation layer affects the interface performance of n-Si and PEDOT:PSS and the reliability of the devices,and how to further improve the photovoltaic performance.These problems restrict the capability of silicon-organic solar cells and their applications.Based on the problems mentioned above,this dissertation focuses on the following four aspects of theoretical and experimental research on silicon-organic hybrid solar cells.The main research contents and innovations are as follows.1)Study on annealing process for the doped PEDOT:PSS film.Firstly,the ethylene glycol?EG?was chosen as dopant to manufacture n-Si/PEDOT:PSS solar cells.The effect of doping concentration and annealing temperature on photovoltaic performance was studied.In the case of 7%concentration and 190 ^oC,the solar cell has the best photovoltaic characteristic.Secondly,the numerical fitting method based on Lambert W function was implemented to fit the experimental results and extract the ideal factor n,series resisitance R_S and shunt resistance R_SH.The characteristics of solar cell versus annealing temperatures are obtained by analyzing the changes of of n,R_S and R_SH with annealing temperature.Finally,based on testing the roughness,resistance and reflectance of PEDOT:PSS film,the film conductivity is increased and the photoelectric conversion efficiency of the solar cell is effectively elevated by improving the PEDOT:PSS film annealing process.2)Study on SiO_x passivation for n-Si/PEDOT:PSS solar cells.Based on the SiO_x passivation layer formed by natural oxidation growth,the effects of passivation layer on surface roughness,hydrophilicity of the solution,built-in potential and light absorption capacity were studied.And also the effect of the positive fixed surface charges in the silicon oxide passivation layer on the improvement of photovoltaic conversion efficiency is analyzed.The positive fixed surface charges could make the energy band bending up and improve the probablilites of light-induced charge carrier cross Si/PEDOT:PSS barrier.In this case,the hybrid solar cell has good photovoltaic characteristics,the best photoelectric conversion efficiency is 13.31%,the short-circuit current is 33.72 mA/cm²,the open circuit voltage V_OCC is 0.607 V,and the corresponding fill factor FF is 65%.3)Study on Al₂O₃ passivation for n-Si/PEDOT:PSS solar cells.The influences Al₂O₃passivation layer on cells performance were studied using alumina grown by ALD on the silicon surface.The quantum efficiency and photoluminescence properties were studied by growing different alumina thicknesses to understand the inherent characteristics of the cells.The hybrid solar cells has a best photoelectric conversion efficiency of 14.84%,its J_SC is34.73 mA/cm²,V_OC is 0.622 V,and FF is 68.67%.By comparing the stability and photovoltaic properties among the alumina passivation layer samples,silicon oxide passivation layer samples and no passivation samples,it is found that the alumina samples have the best conversion efficiency and the lowest dark current density.Howerver the no passivation samples has the best photovoltaic characteristics after 8 days storage,and there are two reasons to cause the deterioration of this kind solar cell.One is the PEDOT:PSS water absorption changes molecule conjugate arrangement leading to hole transparent capacity declined,and the other is the oxide silicon is formed on the Si substrate surface due to the reaction of silicon with oxygen passing through the PEDOT:PSS film and passivation layer onto Si surface,resulting in the series resistance increased.4)Study on the composite hole transport layer of GO and PEDOT:PSS.The 2-D material GO combined with PEDOT:PSS solution was used to form a mixed hole transport layer to improve the transport capacity of the hole transport layer and reduce dark current of device.The coverage features,light absorption capacity,and transient photovoltaic characteristics of the hole transport layer were analyzed by Raman spectroscopy,ultraviolet spectrometer and other testing methods,in which the results indicate that GO is compatible with PEDOT:PSS film and could improve light absorbtion.Compared with single PEDOT:PSS hole transport layer,the recombiantion time of light-induced carriers is increased from 92.5?s to from 99.5?s,which indicate that the composite hole transport layer of GO and PEDOT:PSS could effectively suppress the reconbination of light-induced carriers.