Efficient Infrared Solar Cells Employing Quantum Dot Solids with Strong Inter‐Dot Coupling and Efficient Passivation

Lead chalcogenide quantum dot (QD) infrared (IR) solar cells are promising devices for breaking through the theoretical efficiency limit of single‐junction solar cells by harvesting the low‐energy IR photons that cannot be utilized by common devices. However, the device performance of QD IR photovoltaic is limited by the restrictive relation between open‐circuit voltages (VOC) and short circuit current densities (JSC), caused by the contradiction between surface passivation and electronic coupling of QD solids. Here, a strategy is developed to decouple this restriction via epitaxially coating a thin PbS shell over the PbSe QDs (PbSe/PbS QDs) combined with in situ halide passivation. The strong electronic coupling from the PbSe core gives rise to significant carrier delocalization, which guarantees effective carrier transport. Benefited from the protection of PbS shell and in situ halide passivation, excellent trap‐state control of QDs is eventually achieved after the ligand exchange. By a fine control of the PbS shell thickness, outstanding IR JSC of 6.38 mA cm−2 and IR VOC of 0.347 V are simultaneously achieved under the 1100 nm‐filtered solar illumination, providing a new route to unfreeze the trade‐off between VOC and JSC limited by the photoactive layer with a given bandgap. PbSe quantum dot (QD) infrared solar cells are promising devices for improved photovoltaic performance by harvesting the low‐energy infrared photons unabsorbed by common solar cells. Here, a strategy to protect PbSe QDs is developed via combination of epitaxially coating a thin PbS shell and in situ halide passivation, breaking the VOC–JSC trade‐off in the traditional QD solar cells.