Journal Article polymer solar cells C8-BTBT NIR harvesting Research Support, Non-U.S. Gov't bulk heterojunctions compressive lattice strain conjugated polymers fill factor integrated solar cell interfacial compatibilizers large area nonconjugated polyelectrolytes nucleation and growth processes organic solar cell organic solar cells perovskite solar cell perovskite solar cells phase transitions planar polyelectrolytes printing technology recombination layers single-crystal films tandem polymer solar cells vertical phase separation