Micron Thick Colloidal Quantum Dot Solids

Abstract

Shortwave infrared colloidal quantum dots (SWIR-CQDs) are semiconductors capable of harvesting across the AM1.5G solar spectrum. Today’s SWIR-CQD solar cells rely on spin-coating; however, these films exhibit cracking once thickness exceeds ∼500 nm. We posited that a blade-coating strategy could enable thick QD films. We developed a ligand exchange with an additional resolvation step that enabled the dispersion of SWIR-CQDs. We then engineered a quaternary ink that combined high-viscosity solvents with short QD stabilizing ligands. This ink, blade-coated over a mild heating bed, formed micron-thick SWIR-CQD films. These SWIR-CQD solar cells achieved short-circuit current densities (Jsc) that reach 39 mA cm^–2, corresponding to the harvest of 60% of total photons incident under AM1.5G illumination. External quantum efficiency measurements reveal both the first exciton peak and the closest Fabry–Perot resonance peak reaching approximately 80%—this is the highest unbiased EQE reported beyond 1400 nm in a solution-processed semiconductor.