Although inverted (p-i-n) structure perovskite solar cells (PSCs) have achieved high efficiency by commonly using fullerenes or their derivatives as electron transport layers (ETLs), the device stability and cost of fullerene materials are still of great concern. Herein, we demonstrate inorganic top ETLs simply composed from a family of metal oxides including In2O3 and its derivative of Sn:In2O3 with a gradient potential structure. For inverted PSCs, the typical film formation process of In2O3 will damage or degrade perovskite materials underneath; thus, we report a low temperature synthesis approach for obtaining In2O3 and Sn:In2O3 nanoparticles that can form effective top ETLs without any post-treatment. The one-family oxide-based top ETL features with the enhanced built-in potential, high electron extraction, and low interfacial recombination, offering a power conversion efficiency (PCE) of 20.65% in PSCs constructed from oxide-only carrier (both hole and electron) transport layers (CTLs), which is the highest efficiency in oxide-only CTL-based inverted PSCs to the best of our knowledge. Equally important, the inverted PSCs based on the Sn:In2O3/In2O3 ETL show the excellent operational stability and remain 90% of the initial value of PCE over 2000 h. Consequently, this work contributes to the robust strategy of all oxide-only CTLs in developing rigid and flexible PSCs for practical photovoltaic applications.
Keywords: electron transport layer; inorganic metal oxides; low temperature; perovskite solar cells; solution process.