Device characterization: The current density (J-V) curves were characterized by using an automated Solar Cell I-V test system (Ossila) under AM 1.5G illumination (100 mW/cm) with a class AAA solar simulator (SciSun-150 by ScienceTech). Before each test, the solar simulator was calibrated by reference single-crystal Si cell (ScienceTech). Each sample includes 8 pixels and a total of three samples, or 24 devices were tested under each condition for reliable experimental results.