Studies Of Passivation Materials And Device Structure Of α-Si:H/c-Si Heterojunction Solar Cells

Amorphous silicon/crystalline silicon（α-Si: H/c-Si）heterojunction solar cells is onetypical typeof crystalline silicon solar cells.The performance of the solar cells has been promoting greatly since a structure of insert intrinsic passivation layer between α-Si: H and c-Si,it is one of the key technical factors of high transfer efficiency of Panasonic HIT cell.More and more researchersjoin in the study of HIT solar cellsondevice structure,components and the manufacturing process.This thesis focuses on three points.The first is the influence of thermal-processtemperature to α-Si: H and α-SiO_x: H for n-Cz-Si wafer passivation;the second is feasibility and depositioncontrol mechanism of depositing α-SiO_x: Hto passivate n-Cz-Si by HWCVD;the third is novel α-Si/c-Si heterojunction solar cells structure design and manufacture.The main research content and results are as follows:a)The performance of α-Si: H and α-SiO_x: Hon c-Si wafer passivation has great relation with the substrate temperature during the deposition process and the post-thermal process.The passivation effect of the films deposited atroom temperature is poor.With the deposition substrate temperature increasing,the passivation effect of the films increases and reachs the maximum value at 200²20℃.A similar rule is also found in the effect of he temperature of the post-thermal process on the passivation of the films on c-Si wafers,but the best passivation temperature is happened at 275℃.The optimum recipe of the coupling effect of the substrate temperatureduring deposition process and post-annealingisto deposite at room temperature/100℃（for α-Si: H and α-SiO_x: H respectively）,then post-annealed at 275℃（for both）.The surface recombination rates ofthe c-Si wafer passivated with the optimized α-Si: H and α-SiO_x: Hfilmsare 2.2 cm/s and 3.1cm/s,respectively.b)Si Hx bonds structurein the α-Si:H and α-SiO_x:H films has great effect on the passivation effect of the films to the c-Si wafer surface.The optimal passivation effect got at the relative content of SiH₂ to the total SiH_x（R*）in the films in the range of 0.1⁰.7.c)To make α-SiO_x: Hfilm by HWCVD as the passivation layerfor α-Si: H/c-Si: heterojunction solar cells,the oxidation of the hot wires canbeinhibitedby optimizing processing parameters.The lowest c-Si wafer surface recombination rate is 2.6cm with α-SiO_x: Hfilm passivation by HWCVD,R* of the film is 0.15,deposition rate of which is 0.46nm/s.d)A structure of high-low doped doubleα-Si: H layers（DL）are used as the emitter of α-Si: H/c-Si heterojunction solar cells.According to the simulation and the experimental result,the DL emitter structure could improve the short circuit current of the heterojunction solar cells compared with single layer α-Si: H emitter structure.The mechanisms for this improvement are: a)the improvement of the quantum efficency in the short wavelength range;b)tunneling probability of the current transport increasing with doping concentration in the emitter layers increasing;c)the decrease of the activation energy in the solar cells.e)Adiffused heavy-doped c-Si based BSF（back surface field）structure is designed for α-Si: H/c-Si solar cells.The simulation result shows that the transfer effiency of the α-Si: H/c-Si cells with the back-side structure are better than the normal double-side heterojunction solar cells（HIT）.The improvement comes from the short circuit current increasing.Especially in the condition of the lights injected from the back side of the cells,for the absorption-loss decreases with the new design compared with the α-Si: H based BSF structure.