Simulation Of PERC Solar Cells And The Research Of LBSF Performances

Passivated Emitter and Rear Cell（PERC）has introduced Al₂O₃/Si N_x back passivation layer and laser contact opening（LCO）on the traditional silicon solar cells,forming local aluminum back surface field（LBSF）.Compared with traditional cell,the efficiency of PERC cell is increased more than 1%.The mass production efficiency of Selected Emitter（SE）on single crystal PERC cell has achieved over 22.5%,but compared with the laboratory’s efficiency more than 40.0%,there is still much room for improvement.PERC cell’s LBSF performance directly affects the efficiency（η）and fill factor（FF）,while LBSF of PERC is formed by printing and sintering processes.During sintering,LBSF is prone to voids by the Kirkendall effect.Therefore,The paper uses PC1D simulation software to design the performance of PERC cell,develops an easy-to-operate LBSF filling rate tester and studies the influence of main factors such as passivation layer opening ratio,aluminum paste composition and formula on the performance of LBSF.First,PC1D software used Boltzmann transport equation and Poisson equation,which build a carrier transport and recombination model in the device.By setting basic parameters and variables of the silicon chip,the performance parameters of the cell can be simulated and output.In paper,the basic parameters were reasonably set and parameters including back surface combination rate（SBSF）,sub life（τ）,diffusion concentration in firing area and contact resistance on the cell performance was simulated respectively.The results show that when SBSF increases from 5cm/s to 500cm/s,ηgradually decreases from 22.89%to 21.60%with a decrease of 1.29%;FF increases first and then decreases.It reaches a maximum value of 81.76%when SBSF=200cm/s.Duringτincreased from 100μs to 320μs,ηgradually increased from 21.72%to 22.68%with an improvement of0.96%,while I_sc and V_oc improved 0.05A and 28m V respectively.When the contact resistance increases from 0.2Ω·cm^-2 to1Ω·cm^-2,ηdrops by 1.13%,FF drops by 4.04%,andηand FF are significantly affected by the contact resistance.Then,the paper uses a digital camera with a moderate magnification and high resolution.The camera is the image acquisition hardware structure of the aluminum back-field fill rate.The camera has a built-in CMOS sensor with 6.3 million pixels and a14-150 magnification lens to get high-resolution pictures of LBSF.Using MFC programming and a image processing software HALCON to design the tester software.The software combines the SDK software package to control the operation of the camera and the acquisition of pictures;cooperate with HALCON to call the corresponding algorithm operators to perform processing such as noise reduction and binarization on the image,extract the effective information on the picture,and analyze and calculate the fill rate.The software has the functions of parameter setting,image acquisition,image processing and filling rate calculation.The tester is easy to operate and has high accuracy.It provides an effective testing method for the LBSF performance analysis of PERC cell.Finally,the paper comprehensively uses differential thermal analyzer,scanning electron microscope（SEM）and back surface filling rate tester to study the influence of several main factors on the performance of LBSF.The result shows that LBSF has special requirements for aluminum paste.Compared with traditional aluminum paste,PERC aluminum paste has larger particle size and lower glass melting point.For lead-free glass aluminum paste,when the glass content increases from 0.35wt%to 1.4wt%,the cell efficiency first increases to a maximum and then gradually decreases.When the glass content is 1.05wt%,the battery performance is the best,withηreaching 20.28%;the sintering temperature has a great influence on the cell performance,when the sintering temperature changes in the range of 810℃-920℃,the T4 sample sintered at 900℃has the best performance,ηis 20.43%and FF is 79.98%.