Transport of photogenerated charges and photoelectric properties in two types of heterostructures with different ZnO microstructures

Abstract

ZnO films with several microstructures including nanoparticles, nanowire arrays, nanorod arrays and nanotube arrays were prepared using different methods. In₂O₃ and/or Cu₄Bi₄S₉ were deposited onto each nanostructured ZnO film, and two types of heterostructures (ZnO/Cu₄Bi₄S₉ and ZnO/In₂O₃/Cu₄Bi₄S₉) as well as solid state dye-sensitized solar cells were fabricated. The signals of steady state and electric field-induced surface photovoltage spectroscopy indicate that all of ZnO/In₂O₃/Cu₄Bi₄S₉ heterostructures exhibit higher photovoltaic response than the relative ZnO/Cu₄Bi₄S₉. The same type of heterostructure with different ZnO films presents various photovoltaic properties. Transient surface photovoltage spectroscopy can contribute to study the separation and transport mechanism of photogenerated charges. Here, ZnO nanotubes/Cu₄Bi₄S₉ and ZnO nanotubes/In₂O₃/Cu₄Bi₄S₉ cells exhibit the best performances with the highest efficiencies of 6.2% and 6.8%, respectively. The internal relations of photoelectric properties to some factors, such as film thickness, surface area, microstructure, double energy level matchings, etc. were discussed in detail. Qualitative and quantitative analysis further verified the comprehensive effect and the difference of factors. The exploration to understand the transport mechanism of light-induced charges in composite films will promote the nanocrystal application in solid state solar cells and photovoltaic community.