Recombination Suppression in PbS Quantum Dot Heterojunction Solar Cells by Energy-Level Alignment in the Quantum Dot Active Layers

Using spatial energy-level gradient engineering with quantum dots (QDs) of different sizes to increase the generated carrier collection at the junction of a QD heterojunction solar cell (QDHSC) is a hopeful route for improving the energy-conversion efficiency. However, the results of current related research have shown that a variable band-gap structure in a QDHSC will create an appreciable increase, not in the illumination current density, but rather in the fill factor. In addition, there are a lack of studies on the mechanism of the effect of these graded structures on the photovoltaic performance of QDHSCs. This study presents the development of air atmosphere solution-processed TiO2/PbS QDs/Au QDHSCs by engineering the energy-level alignment (ELA) of the active layer via the use of a sorted order of differently sized QD layers (four QD sizes). In comparison to the ungraded device (without the ELA), the optimized graded architecture (containing the ELA) solar cells exhibited a great increase (21.4%) in...