Solvent-extraction crystal growth for highly efficient carbon-based mesoscopic perovskite solar cells free of hole conductors†
We developed a simple drop-casting method via solvent extraction (SECG) to grow dense and uniform perovskite nanocrystals at room temperature for carbon-based mesoscopic solar cells free of an organic hole-transport layer. The CH3NH3PbI3/N-methyl-2-pyrrolidone (NMP) precursor solution (40%) was first dripped onto a substrate with film configuration TiO2/Al2O3/C and infiltrated at 70 °C for 10 min. The perovskite substrate was next immersed in a bath of diethyl ether at 25 °C for 30 min. Third, the solvent-extracted substrate was stored in a dry box (humidity 50%) at 25 °C for at least 100 h to complete the crystal growth. The device performance attained a power conversion efficiency (PCE) of 12.3%, which is significantly greater than that of DMF (6.3%) and NMP (8.3%) devices using traditional thermal annealing. The SECG device displayed a superior intrinsic enduring stability: the PCE exceeded 12% for 5000 h with a maximum value of 13.3% without light-soaking at 25 °C, but the performance degraded rapidly under one-sun irradiation without encapsulation. To understand the kinetics of charge transfer and defect relaxation for the devices under investigation, we recorded transient photoluminescence decays at an excitation wavelength of 635 nm and a probe wavelength of 770 nm.