Air stability of TiO2/PbS colloidal nanoparticle solar cells and its impact on power efficiency

The short-term (less than 1 hour) exposure of TiO2/PbS quantum dot photovoltaics to air increases the open circuit voltage (Voc) and fill factor (FF) while slightly decreasing the short circuit current density (Jsc), leading to a power conversion efficiency above 4% and a peak external quantum efficiency over 80% for 1.1 eV PbS. The resulting Jsc, Voc, and FF under 100 mW/cm2 AM1.5 are 18.6 mA/cm2, 0.517 V, and 42% for 1.1 eV PbS and 8.03 mA/cm2, 0.655 V, and 35% for 1.7 eV PbS, respectively. Long-term air exposures result in much lower conductivities. Furthermore, short-term air exposure effects are fully reversible upon removal from air, and longer-term effects are mostly reversible through soaking in 1,2-ethanedithiol.