CdTe solar cells with open-circuit voltage breaking the 1 V barrier

Abstract

CdTe solar cells have the potential to undercut the costs of electricity generated by other technologies, if the open-circuit voltage can be increased beyond 1 V without significant decreases in current. However, in the past decades, the open-circuit voltage has stagnated at around 800–900 mV. This is lower than in GaAs solar cells, even though GaAs has a smaller bandgap; this is because it is more difficult to achieve simultaneously high hole density and lifetime in II–VI materials than in III–V materials. Here, by doping the CdTe with a Group V element, we report lifetimes in single-crystal CdTe that are nearly radiatively limited and comparable to those in GaAs over a hole density range relevant for solar applications. Furthermore, the deposition on CdTe of nanocrystalline CdS layers that form non-ideal heterointerfaces with 10% lattice mismatch impart no damage to the CdTe surface and show excellent junction transport properties. These results enable the fabrication of CdTe solar cells with open-circuit voltage greater than 1 V. Solar cells based on CdTe are a promising low-cost alternative to mainstream Si devices, but they usually produce voltages below 900 mV. Burst et al. now show that open-circuit voltages greater than 1 V can be achieved by doping the CdTe with a group V element.