High voltage vacuum-deposited CH3NH3PbI3-CH3NH3PbI3 tandem solar cells

The recent success of perovskite solar cells is based on two solid pillars: the rapid progress of their power conversion efficiency and their flexibility in terms of optoelectrical properties and processing methods. That versatility makes these devices ideal candidates for multi-junction photovoltaics. We report an optically optimized double junction CH3NH3PbI3-CH3NH3PbI3 tandem solar cell where the matched short-circuit current is maximized while parasitic absorption is minimized. The use of an additive vacuum-deposition protocol allows us to reproduce calculated stack designs, which comprise several charge selective materials that ensure appropriate band alignment and charge recombination. This rationalized configuration yields an unprecedented open circuit voltage of 2.30 V. Furthermore, this tandem solar cell features efficiencies larger than 18%, higher than those of the individual sub-cells. Low photo-current values allow reducing the losses associated to the series resistance of transparent contacts, which opens the door to the realization of efficient large area modules.