nc-Si:H/c-Si硅异质结太阳电池中本征硅薄膜钝化层的优化

采用射频等离子体增强化学气相沉积(RF-PECVD)法在低温、低功率的条件下制备了一系列本征硅薄膜, 研究了硅烷浓度(C_S)对薄膜微结构、光电特性及表面钝化性能的影响. 将本征硅薄膜作为钝化层应用到氢化纳米晶硅/晶硅(nc-Si:H/c-Si)硅异质结(SHJ)太阳电池中, 研究了硅烷浓度和薄膜厚度对电池性能的影响. 实验发现: 随着硅烷浓度的降低, 本征硅薄膜的晶化率、氢含量、结构因子、光学带隙和光敏性等都在过渡区急剧变化; 本征硅薄膜的钝化性能由薄膜的氢含量及氢的成键方式决定. 靠近过渡区的薄膜具有较好的致密性和光敏性, 氢含量最高, 带隙态密度低, 且主要以SiH 形式成键, 对硅片表现出优异的钝化性能, 使电池的开路电压大幅提高. 但是, 当薄膜的厚度过小时, 会严重影响其钝化质量. 本实验中, 沉积本征硅薄膜的最优硅烷浓度为6% (摩尔分数), 且当薄膜厚度为~8 nm时, 所制备电池的性能最好. 实验最终获得了开路电压为672 mV, 短路电流密度为35.1 mA·cm^-2, 填充因子为0.73, 效率为17.3%的nc-Si:H/c-Si SHJ太阳电池

Optimization of Intrinsic Silicon Passivation Layers in nc-Si:H/c-Si Silicon Heterojunction Solar Cells

A series of intrinsic silicon thin films were prepared using radio- frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at low temperature and low power density. We investigated the influence of silane concentration (C_S) on the structural, optical, and electronic properties, and passivation quality of the intrinsic silicon films, and the performances of hydrogenated nanocrystalline silicon/crystalline silicon (nc-Si:H/ c-Si) silicon heterojunction (SHJ) solar cells. The results show that with decreasing silane concentration, substantial changes in the crystalline volume fraction, hydrogen concentration, structure factor, optical bandgap, and photosensitivity of the film take place in the transition zone. The passivation quality of intrinsic silicon thin films is decided by the hydrogen content and bonding structure of the film. Films close to the transition zone show good compactness and photosensitivities, high hydrogen content, and low state densities, and contain abundant SiH bonds. The films provide excellent passivation for c-Si surfaces and significantly enhance the open-circuit voltages of nc-Si:H/c-Si SHJ solar cells. However, the passivation quality deteriorates seriously when the film is too thin. In this work, the optimum silane concentration was found to be 6% (molar fraction). By optimizing the film thickness of the passivation layers with C_S=6%, we obtained an nc-Si:H/c-Si SHJ solar cell with an open-circuit voltage of 672 mV, short-circuit current density of 35.1 mA·cm^-2, fill factor of 0.73, and efficiency of 17.3%.