Functionalized porphyrin as a carrier bridge and a passivator for perovskite solar cells

Interfacial modification becomes one of the most emerging strategies in the state-of-the-art perovskite solar cells (PSCs). Here, two porphyrin derivatives (p-MeOTPP, m-DMeOTPP) with different methoxy groups are employed as the modifiers between perovskite and the hole transporting layer (HTL). The interaction at both of perovskite/ modifier and modifier/HTL interfaces, and the hole-transfer ability of the modifier molecule are comprehensively studied, which are jointly responsible for the significant improvement in the optoelectronic properties of the device. More importantly, discussion on a molecular level reveals the distinct roles of modifiers with highly similar structures. A highest power conversion efficiency (PCE) of 24.56% is achieved for m-DMeOTPP modified PSCs, which is attributed to a synergy of efficient passivation effect at perovskite/modifier interface, sufficient built-in potential at modifier/HTL interface and minimal reorganization energy of hole hopping process. pMeOTPP has a stronger passivation ability, but causes unfavorable interfacial dipole at modifier/HTL interface and a large energy barrier when hole's hopping, only resulting in a smaller enhancement. Additionally, both modifers improve the device stability by strongly suppress the immigration of iodine species and moisture penetration. This work presents a synergy mechanism for interfacial engineering to pursue PSCs with high efficiency and stability, and provides practical guidelines at a molecular level to design a modifier not only as an efficient passivator but also as a high-speed carrier bridge.