Optimization of the design of extremely thin absorber solar cells based on electrodeposited ZnO nanowires

The properties of the components of ZnO/CdSe/CuSCN extremely thin absorber (ETA) solar cells based on electrodeposited ZnO nanowires (NWs) were investigated. The goal was to study the influence of their morphology on the characteristics of the solar cells. To increase the energy conversion efficiency of the solar cell, it was generally proposed to increase the roughness factor of the ZnO NW arrays (i.e. to increase the NW length) with the purpose of decreasing the absorber thickness, improving the light scattering, and consequently the light absorption in the ZnO/CdSe NW arrays. However, this strategy increased the recombination centers, which affected the efficiency of the solar cell. We developed another strategy that acts on the optical configuration of the solar cells by increasing the diameter of the ZnO NW (from 100 to 330 nm) while maintaining a low roughness factor. We observed that the scattering of the ZnO NW arrays occurred over a large wavelength range and extended closer to the CdSe absorber bandgap, and this led to an enhancement in the effective absorption of the ZnO/CdSe NW arrays and an increase in the solar cell characteristics. We found that the thicknesses of CuSCN above the ZnO/CdSe NW tips and the CdSe coating layer were optimized at 1.5 μm and 30 nm, respectively. Optimized ZnO/CdSe/CuSCN solar cells exhibiting 3.2% solar energy conversion efficiency were obtained by using 230 nm diameter ZnO NWs.