A new, all room-temperature solution process is developed to fabricate efficient, low-cost, and stable perovskite solar cells (PVSCs). The PVSCs show high efficiency of 17.10% and 14.19%, with no hysteresis on rigid and flexible substrates, respectively, which are the best efficiencies reported to date for PVSCs fabricated by roomtemperature solution-processed techniques. The flexible PVSCs show a remarkable power-per-weight of 23.26 W g(-1). [GRAPHICS] .