Here, we propose a simple, solution-processedtechnological approach to high efficiency tin oxide –based planar perovskitesolar cells (PSCs) with a stabilized power conversion efficiency (PCE) close to21%. In addition, this method yielded remarkable open circuit voltages (V OC )of 1214 mV at a band gap of 1.62 eV confirming the high selectivity of thesolution-processed layers. PSCs aged under 1 sun illumination and maximum powerpoint tracking (MPPT) showed a final PCE of 20.7% after ageing,up from the pre-aged measurement of 20.4%. This approach represents an advancement in the understanding of the roleof electron selective layers (ESLs) on the efficiency and stability of PSCs. We alsoinvestigate (0, 1, 5 and 10 mol.%) Nb-doping of chemical bath deposited SnO 2 and its effect on compositional, structural, optical and electrical propertiesas electron selective layer used in planar-structured PSCs. ESLs with anoptimum 5 mol.% Nb-doping yielded, on average, an improvement of all the devicephotovoltaic parameters with a champion PCE of 20.5% (20.1% stabilized). Dopingchanges carrier concentration at 5 mol.% Nb translating into low device seriesresistance (R s ) in both forward and backward scans, and reducinghysteresis behaviour.
