Investigation on Stability of Halide Treated PbSe Quantum Dot Thin Films for Photovoltaic Devices

PbSe quantum dot solar cells (QDSCs) have great potential for low-cost, high performance photovoltaic devices because of the tunable band gap by wet chemical solution process and excellent performance with multiple exciton generation (MEG). Passivation of PbSe QDs against oxidation is essential for such devices, since the QD solid thin films suffer serious oxidation within hours and degradation in photovoltaic performance. We applied halide treatments directly on PbSe QD thin films and we confirmed the stability of the films has been improved to different extents. We discovered that fluorine treatment did not provide good stability. However chloride, bromide and iodide treatments all improved the stability of the thin films, while the difference is minor within the study period (5 days). We attribute the improvement in stability to the formation of a lead - halide thin layer on the QD surface that serves as a protective layer to oxidation.