Near-Unity Broadband Quantum Efficiency Enabled by Colloidal Quantum Dot/Mixed-Organic Heterojunction

Solution-processed semiconducting materials are promising for realizing high-performance, low-cost, and flexible energy conversion devices. In particular, hybrid structures comprising colloidal quantum dots (CQDs) and organic molecules have been proposed to achieve broadband absorption across the visible-to-infrared solar spectrum. However, the photophysical mismatch present at CQD/organic interfaces limits charge extraction, resulting in low power conversion efficiency (PCE). In this study, we sought to overcome this photophysical mismatch, addressing the CQD/organic interface using a library of surface ligands with different functions. We established, using both experiments and theoretical calculations, that thiol termination of the CQD surface reduced the interfacial barrier, resulting in a 4-fold higher charge transfer efficiency at the maximum power point bias. The CQD/mixed-organic heterojunction solar cells exhibit a record photocurrent density of 33.3 mA/cm2 and near-unity broadband quantum efficiency up to 1100 nm, demonstrating the potential of these devices to harvest infrared solar photons in all-solution-processed tandem devices.