Journal Article dye-sensitized solar cells single-atom catalysts Research Support, Non-U.S. Gov't ZnO nanosheets amorphous structures buried interface cathode reaction composites electrode materials electron selective layers high efficiency iron oxide nonradiative recombination perovskite solar cells perovskites photovoltaic materials platinum quasi-solid reduced graphene oxide self‐assembled molecules solar cells solid-state synthesis sponge-like stability titanium