Inverted organic photovoltaics with a solution-processed Mg-doped ZnO electron transport layer annealed at 150 °C

Abstract

The use of dopants is an effective strategy to improve ZnO electron transport layers (ETLs) for application in solution-processed opto-electronic devices. Mg, in particular, has shown significant promise as a dopant and Mg-doped ZnO ETLs have been used to enhance the performance of a number of solution-processed light-emitting diodes and photovoltaics. However, such a use of Mg to dope ZnO ETLs for organic photovoltaics (OPVs) has remained limited, and only investigated in connection with annealing temperatures of 300 °C or so. In this work, with a view to increase sustainability and compatibility with soft and flexible or foldable substrates, we present OPVs incorporating Mg-doped ZnO ETLs fabricated with annealing temperatures of 150 °C. We demonstrate that Mg doping (≈1% at%) in the ZnO ETL reduces leakage currents and recombination losses in our devices, whilst leaving the morphology of the active layer and the work function of the ETL unaffected. A concomitant increase of the short circuit current density, open circuit voltage and fill factor is also observed, thereby leading to a relative enhancement of the power conversion efficiency by ≈18% compared to devices prepared using undoped ZnO.