PbS AND PbSe QUANTUM DOT SOLAR CELLS: ION EXCHANGE SYNTHESIS AND METAL HALIDE SURFACE PASSIVATION FOR HIGH EFFICIENCY

摘要

Solution-processed photovoltaics represent a promising route forward in reducing the cost of solar energy production. Quantum dot (QD) solids are one such solution-processed system that is being developed. In addition to being solution processable, QD solar cells (QDSCs) have a higher limiting single junction power conversion efficiency than that possible using conventional bulk or thin film semiconductors due to enhanced multiple exciton generation (MEG) in the QDs, thus are of interest for high efficiency, low cost systems. Here, we will describe work where we have developed a direct cation exchange synthesis to produce QDs with a large range of sizes and with in situ chloride and cadmium passivation. The synthesized QDs have excellent air stability, maintaining their photoluminescence quantum yield under ambient conditions for more than 30 days. Furthermore, we explore QDSCs using a metal halide to displace oleate ligands. The resulting QD-solids have a significant reduction in the carbon content compared to films treated with thiols and organic halides. The treatment protocol results in stoichiometric QD films with a deeper work function and band positions than other ligand exchanges. The method developed here produces solar cells that perform well even at film thicknesses approaching a micron, indicating improved carrier transport in the QD films. The best QD solar cells had power conversion efficiencies above 7% for PbS and exceed 6% for PbSe, which is a current record for PbSe QD solar cells.