Robust surface passivation of trap sites in PbS q-dots by controlling the thickness of CdS layers in PbS/CdS quantum dot solar cells

The PbS quantum dot sensitized solar cells were prepared on 3-mercaptoproponic acid (MPA) anchored mesoporous TiO2 films by a successive ionic layer adsorption and reaction (SILAR) process and the fabricated PbS q-dots were passivated by deposition of a CdS layer. In SILAR process, MPA solution was mixed with sulfide precursor solution and used it in every SILAR cycle for rapid conversion of Pb and Cd into their respective sulfides form. Performances of surface passivated and non-passivated PbS q-dot solar cells were compared where solar cells fabricated with q-dots of PbS, PbS/CdS, CdS showed best efficiencies (η) of 1.0, 5.7, 0.9% with current densities (Jsc) of 10.1, 22.8, 2.7 mA cm−2 and open circuit voltages (Voc) of 280, 501, 498 mV respectively. The enhanced efficiency of PbS/CdS q-dot solar cell was mainly due to increase in Jsc and Voc compared to PbS q-dot solar cells. The outstanding performance of PbS/CdS sensitized solar cell was found to be due to reduction of trap states in PbS particle by the surface passivation effect of CdS q-dots and the surface passivation effect of CdS in PbS/CdS sensitized solar cell is reported by EIS and voltage decay investigations.