Mechanism of the Photodegradation of A‐D‐A Acceptors for Organic Photovoltaics**

Abstract

AbstractHerein, we elucidate the photodegradation pathway of A‐D‐A‐type non‐fullerene acceptors for organic photovoltaics. Using IT‐4F as a benchmark example, we isolated the photoproducts and proved them isomers of IT‐4F formed by a 6‐e electrocyclic reaction between the dicyanomethylene unit and the thiophene ring, followed by a 1,5‐sigmatropic hydride shift. This photoisomerization was accelerated under inert conditions, as explained by DFT calculations predicting a triplet‐mediated reaction path (quenchable by oxygen). Adding controlled amounts of the photoproduct P1 to PM6:IT‐4F bulk heterojunction cells led to a progressive decrease in photocurrent and fill factor attributed to its poor absorption and charge transport properties. The reaction is a general photodegradation pathway for a series of A‐D‐A molecules with 1,1‐dicyanomethylene‐3‐indanone termini, and its rate varies with the structure of the donor and acceptor moiety.