Journal Article organic semiconductors perovskite solar cells 2D/3D heterostructures 517-51-1 Fullerenes NP9U26B839 Naphthacenes PTAA QYJ5Z6712R Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. charge transfer charge-transfer state conjugated polymers counterion size electrochemical doping electronic coupling fullerene C60 interface engineering mixed ionic‐electronic conductors naphthacene n‐type semiconductors open-circuit voltage organic electrochemical transistors organic photovoltaic organic solar cell rubrene sidechain engineering small molecules