Fast and feasible fabrication of zinc- and lithium-doped cobalt oxide layers as an emerging hole injection candidate for perovskite solar cells Fatma Pınar Go ¨ kdemir Choi 1, * 1 Faculty of Arts and Science, Department of Physics, Yildiz Technical University, Davutpasa Campus, Esenler, 34210 Istanbul, Turkey Received: 4 January 2021 Accepted: 10 February 2021 Published online: 1 March 2021 Ó The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021 ABSTRACT Metal oxide-based hole injection layers inherent for stable third-generation methylammonium lead tri-iodide (CH 3 NH 3 PbI 3 ) perovskite solar cells. Partic- ularly for inverted types, their structural and optoelectronic properties deter- mine 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 photo- voltaic 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/CoO x :- ZnLi ? /CH 3 NH 3 PbI 3 /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 CoO x employed solar cell devices were changed from 882 to 925 mV, 8.6 to 19.7 mA/cm 2 and 52.6 to 63.9, respectively. The enhancement of the photo- voltaic performances linked to boosted hole mobility and electrical conductivity values for pristine and doped CoO x layers, from 0.55 9 10 -6 cm 2 /Vs to 255 9 10 -6 cm 2 /Vs and from 0.610 to 2.048 lS/cm, respectively. This report reveals the promising hole extraction capability of Zn and Li co-doped cobalt oxide layers for inverted CH 3 NH 3 PbI 3 -based perovskite solar cells. Address correspondence to E-mail: pinargokdemir1984@gmail.com; gokdemir@yildiz.edu.tr https://doi.org/10.1007/s10854-021-05535-z J Mater Sci: Mater Electron (2021) 32:8136–8148