Tailoring the permittivity of passivated dyes to achieve stable and efficient perovskite solar cells with modulated defects

Additive engineering has been demonstrated to effectively mitigate carrier losses associated with high surface defects of perovskite at grain boundaries, bulk, and interfaces. Nevertheless, there are persistent challenges in enhancing the passivation effects at perovskite interfaces without compromising the carrier extraction efficiency. In this work, a feasible strategy incorporating multiple functional groups has been developed to simultaneously passivate defects at grain boundaries/interfaces, and to enhance charge transport by tuning permittivity (εr). Two novel D-π-A type molecules, (Z)-3-((4'-(bis(4-methoxyphenyl)amino)-[1,1′-biphenyl]-4-yl)methylene)-5- fluoroindolin-2-one (TBI) and (Z)-2-(5-((4'-(bis(4-methoxyphenyl)amino)-[1,1′-biphenyl]-4-yl) methylene)-4-oxo-2-thioxothiazolidin-3-yl)acetic acid (TBR) were synthesized. Due to the introduction of the rhodanine acid acceptor, the εr of the dye molecules is significantly increased (εr of TBR is 2.5, εr of TBI is 1.9), making TBR and the εr closer to that of spiro-OMeTAD (εr of spiro-OMeTAD is 2.9), which helps reduce the dielectric mismatch between the top surface of perovskite and HTL. Moreover, the strong coordination interactions with Pb2+/FA+ and SnO2-layer of thioxothiazolidin-3-acetic acid of TBR effectively mitigate the defects at grain boundaries and interfaces. The PSC fabricated based on TBR shows improved VOC, JSC, and FF, resulting in a peak PCE of 23.74 %, along with remarkable stability by maintaining above 86 % of initial performance after 1440 h aging in the air with 60 % relative humidity. This work sets the stage for further improving the performance of perovskite solar cells.