Hybrid perovskites are promising materials for new sustainable photovoltaic applications to operate under low lighting conditions, such as the reuse of residual photons that are wasted during indoor lighting. The requirements for a perovskite solar cell (PSC) to offer maximum power conversion efficiency (PCE) under low illumination conditions are not totally clear in the literature. In this work, the PCE of the commonly used SnO2 electron transport layer (ETL) is improved by a facile method, doping the precursor nanoparticles with small concentrations of a Pb source. Under low illumination conditions (i.e., 0.1 mW cm−2) the PCE is enhanced from 18.8% to 34.2%. From a complete analysis of the ETLs and devices using several structural and electrical techniques it is observed that the parameter that improves the most is the shunt resistance of the device which avoids the parallel leakage of the photogenerated current. The present work clearly shows that the shunt resistance is a very important parameter that needs to be optimized in PSCs for low illumination conditions.

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