ZnO–SnO2 composite anodes in extremely thin absorber layer (ETA) solar cells

ZnO–SnO2 composite electrodes have been deposited on fluorine-doped tin oxide (FTO) substrates by aerosol assisted chemical vapour deposition (AACVD) from a single source precursor solution. The electrodes were characterised using X-ray diffraction (XRD), atomic force microscopy (AFM), field emission gun scanning electron microscopy (FEGSEM) and energy dispersive X-ray analysis (EDX). The composite electrodes were used to construct ETA solar cells with the following structure; FTO/ZnO–SnO2/In2S3/PbS/PEDOT:PSS/Cgraphite/FTO. Performance of the cells were characterised by measuring the current–voltage (I–V) and incident photon to electron conversion efficiencies (IPCE). The effect of Zn:Sn ratio in the precursor and effect of post deposition annealing temperature on the morphology of the composite layers, in relation to the performance of the fabricated cells were investigated. The highest performing cells were fabricated using the composite anode deposited from 50:50 mol% Zn:Sn in the precursor with post deposition annealing at 400 °C. I–V characterisation under AM 1.5 solar simulated light reveals that the cell had an open circuit voltage (Voc) ∼ 0.32 V, short circuit current density (Jsc) ∼ 8.2 mA cm−2, a fill factor (FF) ∼ 0.26, an overall efficiency (η) ∼ 0.68% and a maximum IPCE ∼ 30%. The experimental IPCE agrees well with theoretically estimated IPCE when the PbS surface coverage is about 0.1–0.2.