Colloidal quantum dot (CQD) solar cells have benefited from rapidly rising single-junction efficiencies in recent years and have shown promise in multijunction and color-tuned applications. However, within the context of next-generation solar cells, CQD photovoltaics still have an efficiency deficit compared to mature technologies. Here, we use one-dimensional optoelectronic solar cell simulations to show that much of this efficiency deficit in the highest-performing PbS CQD solar cells can be attributed to the hole transport layer (HTL). We find that increasing both the doping density and, counterintuitively, the electron mobility in this layer should have the largest impact on performance, attributed to the nontrivial role that the HTL plays in photon absorption. We use stoichiometry control through sulfur infusion of the standard CQD HTL materials to improve the carrier mobilities and doping density. This work resulted in a clear performance improvement, to 10.4% power conversion efficiency in the best device.

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