基于BiFeO_3/ITO复合膜表面钝化的黑硅太阳电池性能研究

采用金属银辅助化学刻蚀法在制绒的硅片表面刻蚀纳米孔形成微纳米双层结构,以期获得高吸收率的太阳能电池用黑硅材料.鉴于微纳米结构会在晶硅表面引入大量的载流子复合中心,利用磁控溅射技术在黑硅太阳电池表面制备了BiFeO_3/ITO复合膜,并对其表面性能和优化效果进行了探索.实验制备的具有微纳米双层结构的黑硅纳米线长约180—320 nm,在300—1000 nm波长范围内入射光反射率均在5%以下.沉积BiFeO_3/ITO复合薄膜后的黑硅太阳能电池反射率略有提高,但仍然具有较强的光吸收性能;采用BiFeO_3/ITO复合膜的黑硅太阳能电池开路电压和短路电流密度分别由最初的0.61 V和28.42 mA/cm~2提升至0.68 V和34.57 mA/cm~2,相应电池的光电转化效率由13.3%上升至16.8%.电池综合性能的改善主要是因为沉积BiFeO_3/ITO复合膜提高了电池光生载流子的有效分离,从而增强了黑硅太阳电池短波区域的光谱响应,表明具有自发极化性能的BiFeO_3薄膜对黑硅太阳能电池的表面性能可起到较好的优化作用.

Performance investigation of black silicon solar cells with surface passivated by BiFeO3/ITO composite film

In order to prepare black silicon material with excellent optical absorption performance for solar cell application, a micro/nano bilayer-structure is formed on the surface of textured silicon wafer by a silver assisted chemical etching method. It is found that the deeper nanoholes could form as the etching time is longer, and the surface reflectivity is reduced obviously due to the increased time of photon reflection from the nanowires. The incident light reflectivity of the prepared black silicon is significantly reduced to 2.3%, showing obviously better optical reflectance characteristics than general monocrystalline silicon wafer, especially in a wavelength range of 300-830 nm. Considering the fact that a large number of carrier recombination centers is introduced into the nanostructured crystal silicon surface, BiFeO₃/ITO composite film is coated on the surface of the black silicon solar cell by magnetron sputtering process to optimize the surface defect states and improve the cell performance. The experimental results show that the lengths of the nanowires are predominantly in a range of 180-320 nm for the prepared black silicon with micro/nano double-layer structure. The reflectivity of the incident light is below 5% in a wavelength range from 300 nm to 1000 nm, and reaches a maximal value at about 700 nm. The reflectance increases slightly as BiFeO₃/ITO composite film is coated on the surface of black silicon solar cell, but it is still much lower than that of general monocrystalline silicon solar cell. The open circuit voltage and short circuit current density of the black silicon solar cell increase respectively from 0.61 V to 0.68 V and from 28.42 mA/cm² to 34.57 mA/cm² after it has been coated with BiFeO₃/ITO composite film, and the photoelectric conversion efficiency of the cell increases from 13.3% to 16.8% accordingly. The improvement in performance of black silicon solar cell is mainly due to the promotion of effective separation of photogenerated carriers, thereby enhancing the spectral response of black silicon solar cell in the whole wavelength range. This indicates that the spontaneously polarized BiFeO₃ film can play a better role in improving the surface properties of black silicon solar cell. On the other hand, for the BiFeO₃ film deposited on the surface of black silicon, a spontaneous polarization positive electric field could be produced, pointing from the film surface to the inside of the solar cell. This polarization electric field could also act as part of built-in electric field to contribute the photoelectric transformation of the black silicon solar cell, leading to the open circuit voltage of cell increasing from 0.61 V to 0.68 V.