Construct efficient CsPbI2Br solar cells by minimizing the open-circuit voltage loss through controlling the peripheral substituents of hole-transport materials

In order to further boost the photovoltaic performance of all-inorganic perovskite solar cells (PSCs), great efforts are needed to synergistically develop high-quality perovskite film and highly efficient charge transport materials. In view of the fact that large number of researchers have devoted to optimizing the crystal composition and crystallization kinetics, we chose to carry out the study from the perspective of hole transport layer. Herein, we designed and synthesized two low-cost fluorene terminal-modified hole transport materials (HTMs), termed YT-MPF and YT-FF. Moreover, through the modification of peripheral groups, the electrostatic surface potentials of HTMs are well regulated. The HTM YT-MPF with one peripheral fluorene arm on each side exhibits a more polarized structure, which facilitates the intermolecular interaction and hole hopping transport. Applied YT-MPF in CsPbI2Br based all-inorganic PSC, an impressive power conversion efficiency (PCE) of 16.0% with fairly high open-circuit voltage (V-oc) of 1.29 V is obtained, outperforming that of the control devices based on traditional HTM PTAA (12.7%) and Spiro-OMeTAD (14.7%). Our research supplies an effective way to push up the performance of CsPbI2Br PSC.