PbTe Quantum Dots and Engineering of the Energy Band Alignment in Photovoltaic Applications

Lead telluride (PbTe) quantum dots, despite being considered as one of the most promising candidates for future photovoltaics owing to their higher multiple exciton generation yields, have received limited attention in solar cell designs due their less explored surface chemistry and high air sensitivity. This study demonstrates the synthesis and characterization of highly crystalline PbTe QDs and their utilization in solution processed solar cells through band alignment engineering. Ultraviolet photoelectron spectroscopy studies showed that the conduction and valence band levels depend strongly on the type of surface ligand utilized for the ligand exchange process. Conduction and valence band levels of tetrabutylammonium iodide (TBAI) and 1,2-ethanedithiol (EDT) treated PbTe QDs with respect to vacuum were measured as -3.73 eV/-4.83 eV and -3.48 eV/-4.45 eV, respectively. The presence of a band offset between the conduction and valence band levels of TBAI and EDT treated layers allowed us to engineer the band alignment in the light absorbing layer. As a result, solar cells where TBAI and EDT ligand treated QDs were utilized in a bilayer cell architecture reached a photo conversion efficiency of 0.65%.