Indacenodithieno[3,2-b]thiophene-Bridged Fullerene for Defect Suppression in Perovskite Photovoltaics

Defects at the bulk and grain boundaries of perovskites, along with weak n-type surface characteristics, remain critical obstacles to enhance the power conversion efficiency (PCE) of the perovskite solar cells (PSCs). Herein, an acceptor–donor–acceptor (A-D-A) type organic passivator structured with two C₆₀ cages sandwiching a nonfullerene acceptor fragment indacenodithieno[3,2-b]thiophene (IT), namely C₆₀-IT-C₆₀, is designed. Morphological and spectroscopic measurements demonstrate that the S element in the IT unit and the fullerene cages of C₆₀-IT-C₆₀ act as a Lewis base and acid to passivate the uncoordinated Pb²⁺ cation and anion defects. This interaction not only aligns the energy diagram and work functions of perovskite, but also encourages the crystallization of perovskite and suppresses the deep- and shallow-level defects, leading to a maximum PCE of 24.16% (fill factor of 84.75%) with improved storage and thermal stability in the corresponding PSCs. This work provides a new design paradigm of fullerene derivatives in PSCs.