Stepwise-Process-Controlled Ligand Management Strategy for Efficient and Stable Perovskite Quantum Dot Solar Cells.

CsPbI perovskite quantum dots (QDs) have attracted much attention in the field of solar cells because of their excellent photovoltaic properties. Conventional modification of long-chain insulating ligands can ensure good dispersion and film-forming stability of QDs, but the limitations of their low defect passivation ability and poor charge transport ability will make them fail to achieve high efficiency in the corresponding solar cell devices. In this study, by introducing "Benzylphosphonic acid" short-chain ligands to the surface of CsPbI QDs, the ligands were re-administered on the surface during the preparation of the CsPbI QDs as well as during the film-forming process. The strong coordination ability of Benzenephosphonic acid can effectively passivate defects on the surface of CsPbI QDs and inhibit non-radiative recombination and phase transition. Meanwhile, this short-chain ligand can effectively promote the charge exchange between adjacent QDs and improve the electrical transport properties of the film. The efficiency of the Benzylphosphonic acid-modified CsPbI QDs solar cell reaches 13.91% compared to the unmodified device (PCE of 11.4%). The storage stability and operation stability of the device are also significantly improved. (The efficiency remains at 91% of the original for 800 h of atmospheric storage; the efficiency remains at 92% of the original for 200 h of continuous light exposure.) The present strategy realizes the simultaneous improvement of photovoltaic properties and stability of CsPbI QD solar cells and also provides a reference for surface ligand engineering to realize highly efficient and stable perovskite quantum dot solar cells.