Design And Preparation Of The Double-layer Emitter Structured Silicon Based Heterojunction Solar Cells

With the development of photovoltaic industry, a-Si:H/c-Si heterojunction solarcells have attracted attentions of many research institutions. Recently, Panasonicadopted a back-contact HIT solar cell structure, with the electrodes on the back of thesolar cell. It is announced that it has achieved a new world record with the conversionefficiency of25.6%(AM1.5, cell area:143.7cm2). In this paper, passivation c-Sisurface by a-SiOx:H has been studied. Double-layer emitter structured silicon basedheterojunction (DLE-SHJ) solar cell has been stimulated and munufactured. Theresults of theoretical simulation and experimental validation could be described asfollowing:Comparing with the effect of intrinsic a-Si:H, the effect of intrinsic is morestable on the surface passivation of c-Si surface. The optimized parameters fora-SiOx:H films by PECVD method are: substrate temperature=200oC, gas flow ratio(H2:SiH4:CO2)=15.0sccm:3.0sccm:0.6sccm, ratio frequence power=12W anddeposition pressure=22Pa. With the effective minority carrier lifetime and surfacerecombination velocity of the n-type c-Si wafer di-facial passivated by the a-SiOx:Hfilms with the optimized parameters reaches1893μs and4cm/s, respectively.Simulation with AFORS-HET program is done to analyze the proposedDLE-SHJ solar cells. It is found that compared with the traditional single-layeremitter structured silicon based heterojunction (SLE-SHJ) solar cells, the short circuitcurrent and open circuit voltage of the DLE-SHJ solar cells are both improved, andseries resistance is decreased. An enhancement of external quantum efficiency ispresented in the range of300nm-600nm, which lead to a0.7%absolutely increase inconversion efficiency.The optimizing researches of doping concentration have been carried out for theSLE-SHJ solar cells and the DLE-SHJ solar cells. The results show that: comparedwith the optimum SLE-SHJ solar cells, the conversion efficiency(AM1.5) of theoptimum DLE-SHJ solar cells has increased by2.8%absolutely and the values of theexternal quantum efficiency of the DLE-SHJ cells is higher than those of the SLE-SHJ cells in the range of300nm-600nm, which is consistent with thesimulation results. So it is thought that the DLE structure is really have some effectfor increasing the transfer efficiency of the silicon-based heterojunction solar cells.