Enhanced photovoltaic performance of nanocrystalline CdTe/ZnO solar cells using sol-gel ZnO and positive bias treatment

Abstract

The effect of doping and porosity of the n-type ZnO layer on the performance of solution-processed, sintered p-CdTe/n-ZnO nanocrystal photovoltaic (PV) devices is investigated. Amorphous sol-gel ZnO is found to be the best candidate with overall energy conversion efficiencies above 8% obtained if the ZnO is also indium doped. We demonstrate that when such PV devices are left under forward bias (in dark or light), the device efficiency values are raised to at least 9.8%, due to a substantially increased open-circuit voltage and fill-factor. This drastic enhancement is attributed to improved band alignment at the ITO/CdTe interface. The forward-bias treatment is slowly reversed over a period o..