Research On The Tunneling Oxide Layer Passivation Contact (TOPCon) Solar Cell

Photovoltaic technology has been widely used because of its high efficiency,cleanliness and inexhaustible advantages.In the development of solar cells,improving the efficiency and reducing the cost are the two eternal themes.The most widely used solar cells in the industry are the traditional crystalline silicon cells,which are mainly p-type crystalline silicon.The PERC solar cell,limited by the structure design,is difficult to increase the conversion efficiency of more than 23%furthermore.Thus,it is important to develop a more efficient solar cell.This thesis mainly studies the high-efficiency crystalline silicon solar cell,Tunnel Oxide Passivated Contact Solar Cell?TOPCon?,which has developed rapidly in recent years.This solar cell features high-quality ultra-thin silicon oxide and a doped polysilicon layer for the excellent full-surface passivation and the selective carrier collection.Also,eliminating the silicon/metal contact is beneficial to increase the open circuit voltage(V_oc)and to improve the fill factor?FF?.In addition,the solar cell using a high-quality n-type crystalline silicon wafer avoids the light-induced degradation phenomenon of the p-type silicon wafer,leading to the stable high efficience.This work is mainly devoted to develop a high-efficiency TOPCon solar cell preparation process,which improves efficiency by step-by-step optimization of each process.While exploring the cell preparation process,the following aspects have been studied:1.High-quality tunneling SiO_x layer was prepared by hot nitric acid oxidation method.The relationship between thickness and solution temperature and preparation time was studied.We control the SiO_x thickness of about 1.5 nm as the high-efficiency tunneling layer.XPS was used to analyze the quality of SiO_x,and the TOPCon passivation structure was prepared by PECVD deposition of phosphorus-doped amorphous silicon followed by the high-temperature crystallization annealing.By optimizing the deposition parameters and the annealing process,the excellent surface passivation was achieved.The crystallization rate and doping concentration of the phosphorus-doped polysilicon were analyzed by Raman and ECV.The implied open circuit voltage(iV_oc)average exceeds 725mV.After further hydrogenation treatment,the iV_oc up to 747mV is achieved.Besides,the passivation and anti-reflection effects of the AlO_x/SiN_x stack layer were investigated and optimized.The refractive index of SiN_x was precisely controlled by software simulation and experimental parameters to suit the preparation of the TOPCon solar cell anti-reflection layer,which provided a guideline for the preparation of high-efficiency TOPCon solar cells..2.The contact resistance of TOPCon structure was studied.The atomic force microscopy?AFM?and conductive atomic force microscopy?c-AFM?and TOPCon structure J-V characteristics and software simulation were used to study the carrier transportation of TOPCon structure.The synergistic effect of pinhole transmission and the influences of pinhole transmission current on TOPCon solar cell parameters were studied?3.The effects of different post-treatment methods on the hydrogen injection effect of TOPCon passivation layer were studied.Also,we developed a post-annealing process with water vapor,which was simple,useful,and suitable for industrial manufacture.The water-vapor post-annealing typically leads to the improvement of surface passivation by 15-25mV.The TOPCon structures treated or without treated by the water-vapor post-annealing was analyzed by the secondary ion mass spectrometer?SIMS?.Through the optimization,the maximum efficiency of the TOPCon solar cell in our laboratory achieved 22.15%.