Molecular Doping of the Hole-Transporting Layer for Efficient, Single-Step-Deposited Colloidal Quantum Dot Photovoltaics

Employment of thin perovskite shells and metal halides as surface-passivants for colloidal quantum dots (CQDs) has been an important, recent development in CQD optoelectronics. These have opened the route to single-step-deposited high-performing CQD solar cells. These promising architectures employ a CQD hole-transporting layer (HTL) whose intrinsically shallow Fermi level ( E F ) restricts band-bending at maximum power-point during solar cell operation limiting charge collection. Here, we demonstrate a generalized approach to effectively balance band-edge energy levels of the main CQD absorber and charge-transport layer for these high-performance solar cells. Briefly soaking the CQD HTL in a solution of the metal–organic p-dopant, molybdenum tris(1-(trifluoroacetyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), effectively deepens its Fermi level, resulting in enhanced band bending at the HTL:absorber junction. This blocks the back-flow of photogenerated electrons, leading to enhanced photocurrent and fill factor compared to those of undoped devices. We demonstrate 9.0% perovskite-shelled and 9.5% metal-halide-passivated CQD solar cells, both achieving ca. 10% relative enhancements over undoped baselines.