Study On The Photoelectric Performance Of High Bifaciality And High Resistance Dense Grid PERC Cell

Solar energy is safe,green and renewable energy source.Solar cells are the core devices that directly convert solar energy into electrical power.The development of solar cells with high conversion efficiency and low production cost is of great scientific and technical interests.At present,the conversion efficiency of conventional crystalline silicon passivated emitter and rear(PERC)crystalline silicon solar cells in mass production is 22.04%.The further improvement of solar cells efficiency has encountered a bottleneck,and there is an urgent need to develop innovative technologies and processes.This work focuses on,the improvement of the emitter and rear electrode of crystalline silicon for in-line silicon PERC solar cells.low pressure three-step diffusion,selective dot-matrix laser doping,stacked passivation layers,and narrow-gap fingers are proposed for improving the in-line cell conversion efficiency.The bifacial PERC cells have been studied as well.This work contains paper the following aspects:(1)The three-step preparation of PN junctions under low-pressure conditions and cascade heating mode was studied.By adjusting the diffusion parameters like:diffusion temperature,oxygen flow rate,small nitrogen gas flow rate,diffusion time,the square resistance can be tuned.A target high square resistance of 180 Ω/□ was obtained at diffusion temperature of 790℃ and small nitrogen gas flow rate of 520 sccm.As the square resistance increases,the average minority carrier life increases initially and then saturates.Additionally a heavily doped area beneath the metal finger contact was prepared by using laser selective doping(Selective Emitter)to form an Ohmic contact and reduce the metal-semiconductor contact resistance.After diffusion,the undoped region on the emitter surface and the laser selective doped region form a high and low junction,which is beneficial for the carrier transportation.(2)In order to match with the high square resistance front emitter,the electrode preparation process was studied and optimized in aspects of.finger number of different screens and finger width.Given the theoretical analysis and simulation the optimal finger number is 114 taking the optical performance into consideration.Taking advantage of high-square-resistance emitters and narrow finger gap,the in-line cell efficiency reaches 22.32%with an increase of 0.28%.(3)A new rear-side dashed laser scribing process is proposed.Compared with the traditional parallel linear laser scribing,the proposed laser scribing method lead to reduced the damage of the passivation layer.The average lifetime of carriers increases consequently.A bifacial PERC cell with a bifacial rate of 76.86%was achieved,with a front efficiency of 22.34%and a back efficiency of 17.17%.(4)The SiO2/Al2O3/SiNx layer stack was designed for improved passivation and anti-reflection effect on the rear side.The sintering process was adjusted accordingly.The best sintering temperature was 840℃.Finally the bifacial ratio of was further increased to 77.27%,with a front efficiency of 22.44%and a back efficiency of 17.34%.In summary,this paper systematically analyzes and optimizes the structure and process of the emitter and back electrode of in-line crystalline silicon PERC solar cells.The diffusion conditions are optimized by the three-step diffusion technology to form a high square resistance,and the front PREC is matched with the narrow finger gap technology.Using SiO2/Al2O3/SiNx stacked passivation and anti-reflection structures and a new lattice complementary parallel laser slotting pattern technology,high bifacial ratio PERC cells were achieved.