Photoelectrical Characterisation and Modelling of the Eta-Solar Cell

Eta-solar cells were fabricated and analysed, these are thin film solar cells with an extremely thin absorber (here p-type CdTe) and a nano- or microstructured n-type TiO2 layer. The illuminated I-V curves are S-shaped. Quantum efficiency curves were measured under forward and reverse voltage bias, with and without light bias, and with varying front and back side illumination. These characteristics were analysed using the quantitative simulation program SCAPS-1D. Although this one-dimensional model is intended for simulation of planar solar cells, it does simulate the typical features of the I(V) and QE(λ) curves fairly well. A fair simulation of the experimentally measured S-shaped I(V) curves is obtained, as well as a qualitative simulation of the measured QE(λ) curves, by the assumption of a rather large conduction band offset (conduction band of CdTe 0.7 eV higher than of TiO2) together with tuning of CdTe materials parameters doping concentration and electron lifetime.