Novel dual-modification strategy using Ce-containing compounds toward high-performance flexible perovskite solar cells

The carrier non-radiative recombination loss caused by numerous interfacial defects existing between perovskite and neighboring charge transport layers, such as SnO 2 /perovskite and perovskite/spiro-OMeTAD, which greatly restricts the performance improvement of flexible perovskite solar cells (PSCs). Herein, we devised a novel dual-modification strategy using Ce-containing compounds (Ce 2 (SO 4 ) 3 and Ce(SO 4 ) 2 ) to minimize interfacial defect density at the interface of SnO 2 /perovskite and perovskite/spiro-OMeTAD respectively, thus enhancing the performance and stability of flexible PSCs. It was revealed that the introduction of Ce 2 (SO 4 ) 3 interface layer was conducive to ameliorating the electrical properties of SnO 2 and significantly reducing the SnO 2 /perovskite interface defects. Moreover, the Ce(SO 4 ) 2 was adopted as a novel oxidant to achieve the rapid oxidation of spiro-OMeTAD, thus enhancing the hole mobility of bulk spiro-OMeTAD and suppressing perovskite/spiro-OMeTAD interface defects. Therefore, reduced non-radiative recombination losses near the two interfaces of the perovskite layer could be achieved by such a novel and comprehensive modification strategy. In consequence, the Ce-modified flexible and rigid PSCs achieved excellent photoelectric conversion efficiency (PCE) of 19.34 % and 22.62 %, respectively. Notably, the optimized flexible PSCs exhibited outstanding mechanical durability, and 83.2 % of the initial PCE was maintained after 3000 bending cycles.