Lead halide perovskite solar cells that use SnO2 as the electron transporting material are known to improve upon light soaking. Photoluminescence measurements and electrochemical impedance spectroscopy show that this improvement is due to reduced non-radiative recombination and is accompanied by a reduction in the extrinsic electron concentration in SnO2. This performance enhancement can also be achieved by exposing these devices to high vacuum at ambient temperature. We postulate that the performance increase stems from desorption of hydrogen from oxygen vacancies in SnO2. Furthermore, Ga-doped SnO2 based devices exhibit a reduced light soaking effect and have fewer oxygen vacancies, as is shown by XPS measurements. We conclude that high extrinsic electron concentrations in SnO2 are undesirable because of their role in non-radiative recombination. The reduction in electron density when SnO2 is incorporated into a perovskite diode is therefore advantageous for solar cell performance.