Modeling and characterization of extremely thin absorber (eta) solar cells based on ZnO nanowires.

Extremely thin absorber (eta)-solar cells based on ZnO nanowires sensitized with a thin layer of CdSe have been prepared, using CuSCN as hole transporting material. Samples with significantly different photovoltaic performance have been analyzed and a general model of their behavior was obtained. We have used impedance spectroscopy to model the device discriminating the series resistance, the role of the hole conducting material CuSCN, and the interface process. Correlating the impedance analysis with the microstructural properties of the solar cell interfaces, a good description of the solar cell performance is obtained. The use of thick CdSe layers leads to high recombination resistances, increasing the open circuit voltage of the devices. However, there is an increase of the internal recombination in thick light absorbing layers that also inhibit a good penetration of CuSCN, reducing the photocurrent. The model will play an important role on the optimization of these devices. This analysis could have important implications for the modeling and optimization of all-solid devices using a sensitizing configuration.