In-situ entropic ligand engineering enables high-efficiency quantum dot solar cells.

Metal halide perovskite quantum dots (PQDs), particularly formamidinium lead triiodide (FAPbI3) PQDs, have garnered significant attention for high-efficiency solar cells due to their ideal optical properties and stable phase structure. However, achieving desired colloidal dispersion and charge transport of FAPbI3 PQDs still remains challenging. Herein, we report an efficient in-situ entropic ligand engineering strategy, using bis(2-ethylhexyl) phosphate (DEHP), to achieve improved dispersibility and charge transport in organic-inorganic hybrid FAPbI3 PQDs. The branched 2-ethylhexyl tails of DEHP increase configurational entropy, improving solvent interaction and colloidal stability. In addition, the phosphinic acid head anchoring group of DEHP exhibits stronger binding strength for enhanced surface passivation and reduced core-core interactions. By optimizing the addition of entropic ligand, the DEHP-capped PQDs exhibit high colloidal stability and favorable optical properties, resulting in a power conversion efficiency (PCE) of 18.68% (certified value 18.23%) for PQD solar cells, along with improved stability. We believe these findings would provide insights to the design and synthesis of metal halide PQDs to construct desired films for optoelectronic applications.