Solution-processed infrared quantum dot solar cells

Colloidal quantum dots (CQDs) are solution-processed semiconductors of interest in low-cost photovoltaics. Tuning of the bandgap of CQD films via the quantum size effect enables customization of solar cell's absorption profile to match the sun's broad visible- and infrared-containing spectrum reaching the earth. Here we review progress in the realization of low-cost, efficient solar cells based on CQDs. We focus in particular on CQD materials and approaches that provide both infrared and visible-wavelength solar power conversion. CQD photovoltaics now exceed 5% solar power conversion efficiency, which has been achieved by the introduction of a new architecture, the depleted-heterojunction CQD solar cell, that jointly maximizes current, voltage, and fill factor. CQD solar cells have also seen major progress in materials processing for stability, achieving extended operating lifetimes in an air ambient. We summarize progress both in device operation and also in gaining new insights into materials properties and processing – including new electrical contact materials and deposition techniques, as well as CQD synthesis, surface treatments, film-forming technologies – that underpin these rapid advances. Introduction Single-crystal materials such as silicon and epitaxial III–V compound semiconductors have led to remarkable solar photovoltaic power conversion efficiencies in the range of 20–41.4% [1, 2]. For their high efficiencies, these devices rely on the efficient matching of the light absorption spectrum to that of the sun's power reaching the earth, combined with the excellent electronic transport properties of crystalline semiconductors.