Colloidal Quantum Dot Bulk Heterojunction Solids with Near‐Unity Charge Extraction Efficiency

Colloidal quantum dots (CQDs) are of interest for optoelectronic applications owing to their tunable properties and ease of processing. Large-diameter CQDs offer optical response in the infrared (IR), beyond the bandgap of c-Si and perovskites. The absorption coefficient of IR CQDs (≈104 cm-1) entails the need for micrometer-thick films to maximize the absorption of IR light. This exceeds the thickness compatible with the efficient extraction of photogenerated carriers, a fact that limits device performance. Here, CQD bulk heterojunction solids are demonstrated that, with extended carrier transport length, enable efficient IR light harvesting. An in-solution doping strategy for large-diameter CQDs is devised that addresses the complex interplay between (100) facets and doping agents, enabling to control CQD doping, energetic configuration, and size homogeneity. The hetero-offset between n-type CQDs and p-type CQDs is manipulated to drive the transfer of electrons and holes into distinct carrier extraction pathways. This enables to form active layers exceeding thicknesses of 700 nm without compromising open-circuit voltage and fill factor. As a result, >90% charge extraction efficiency across the ultraviolet to IR range (350-1400 nm) is documented.