Defects, photophysics and passivation in Pb-based colloidal quantum dot photovoltaics

Colloidal quantum dots (CQDs) are a class of third-generation materials for photovoltaics (PVs) that are promising for enabling high efficiency devices with potential for exceeding the Shockley-Queisser limit. This is due to their potential to decrease thermal dissipation via multiple exciton generation during charge conversion and collection, which could potentially lead to an increase in the photovoltage or photocurrent in colloidal quantum dot photovoltaics (CQD PVs). But despite a predicted upper efficiency limit of 42%–44%, the highest power conversion efficiencies of these PVs using lead sulfide colloidal quantum dots (PbS CQDs) remains at approximately 13% on a laboratory scale. For further improvements, the fundamental recombination mechanisms need to be studied to determine their effects on the open-circuit voltage (VOC) and charge-carrier lifetime as well as the diffusion length of the carriers. Also, surface defect passivation and interface engineering should be studied. In this work, we discuss different pathways for non-radiative recombination losses in lead sulfide colloidal quantum dot photovoltaics (PbS CQD PVs), as well as the strategies for reducing these losses by the passivation of the surface and interface defects. We also discuss routes to overcome limits in the diffusion length of the carriers through the engineering of charge transport layers. This work provides routes for the fabrication of highly efficient CQD PVs.