Reduced recombination with an optimized barrier layer on TiO₂ in PbS/CdS core shell quantum dot sensitized solar cells

Fast electron transport and slow interfacial electron recombination are indispensable features for efficient photo-electrodes of quantum dot sensitized solar cells (QDSSCs). This study reports the methodology to prevent recombination losses in lead sulfide QDSSCs. TiO₂ nano-particles were coated with two different insulating oxide materials (MgO and Al₂O₃). Single- and-double coated barrier layers are used in order to optimize the passivation effect, prevent recombination losses and to obtain high-performance stable QDSSCs when compared to bare TiO₂. Metal oxides with a high isoelectric point enhance quantum dot adsorption and also increase the TiO₂ conduction band edge. QDSSCs are examined in detail using a polysulfide electrolyte and a copper sulfide (CuS) counter electrode. A solar cell based on a double coating electrode (MgO/Al₂O₃) yielded excellent performance with an efficiency (η) of 3.25%. The increase in electron transport and the decrease in electron recombination are responsible for the enhanced J_SC and V_OC of QDSSCs. The electron lifetime with TiO₂/MgO/Al₂O₃ was higher than those with bare TiO₂, TiO₂/MgO, TiO₂/Al₂O₃ and TiO₂/Al₂O₃/MgO leading to a more efficient electron-hole separation and slows down electron recombination.