Bandgap, window layer thickness, and light soaking effects on PbS quantum dot solar cells

We have studied the dependence of PbS quantum dot (QD) solar cell performance on the QD bandgap energy, window layer material and thickness, and light-soaking. Our best device, based on a ZnO/PbS-QD heterojunction design, demonstrates V_OC of 0.6 V, J_SC of 15.6 mA cm^-2, FF of 44% and photovoltaic conversion efficiency of 4.1%. The current voltage characteristics of these devices show a QD size (bandgap) dependent behavior. Light soaking studies show improvement in the performance of Schottky junction and heterojunction devices, including those using a CdS window layer. The light-soaking-induced enhancement is greatest in heterojunction devices, and reverses upon termination of light soaking. Preliminary assessment indicates that light soaking improves the QD-QD interfaces through photochemical passivation.