Fast and feasible fabrication of zinc- and lithium-doped cobalt oxide layers as an emerging hole injection candidate for perovskite solar cells

Abstract

Metal oxide-based hole injection layers inherent for stable third-generation methylammonium lead tri-iodide (CH3NH3PbI3) perovskite solar cells. Particularly for inverted types, their structural and optoelectronic properties determine the limit of the power conversion efficiencies. This work demonstrates a novel cobalt oxide-based hole injection layer (HIL) and metal doping effect on its performance. Using a fast and feasible solution-based route and employing Zn and Li as dopant sources, a systematic study is presented through photovoltaic performances. Structural and morphological properties and the effect of doping on the hole injection layers were examined through surface roughness, electrical and hole conductivity, bandgap, and crystalline structure analysis. In ambient air, glove-box free fabrication with a configuration of ITO/CoOx:ZnLi+/CH3NH3PbI3/PCBM/BCP/Ag boosted the efficiency up to 11.64 % from 3.99 % for pristine cobalt oxide employed devices. By employing optimum Zn and Li co-doping, open-circuit voltage, short-circuit current, fill factor of the pristine CoOx employed solar cell devices were changed from 882 to 925 mV, 8.6 to 19.7 mA/cm2 and 52.6 to 63.9, respectively. The enhancement of the photovoltaic performances linked to boosted hole mobility and electrical conductivity values for pristine and doped CoOx layers, from 0.55 × 10-6 cm2/Vs to 255 × 10-6 cm2/Vs and from 0.610 to 2.048 µS/cm, respectively. This report reveals the promising hole extraction capability of Zn and Li co-doped cobalt oxide layers for inverted CH3NH3PbI3-based perovskite solar cells.