Journal Article 2D perovskites Research Support, U.S. Gov't, Non-P.H.S. Review Ruddlesden−Popper Thiophenes all‐polymer solar cell charge transfer charge transport electrical conductivity exciton dissociation flexible materials interpenetrating network structure ionic thermoelectrics molecular structures multimodal nanocomposites n‐doping n‐type ionogel optoelectronics organic solar cells piezoelectric poly(3-hexylthiophene) polymer acceptor sensor star‐shaped nonfullerene acceptor ternary device thermoelectric materials three‐dimensionality