Inverted Schottky quantum dot solar cells with enhanced carrier extraction and air-stability

We introduce a novel colloidal quantum dot solar cell (CQD SC) architecture, defined as inverted Schottky CQD SCs, which consists of a thin film of PbS CQDs sandwiched between a low-work-function, transparent conducting oxide (Lϕ-TCO) and a high-work-function metal anode. On Lϕ-TCO substrates, which were generated by coating a thin layer of polyethylenimine (PEI) onto FTO, a series of inverted Schottky CQD SCs with varied PbS CQD sizes and QD layer thicknesses were fabricated and characterized using capacitance–voltage (C–V), current–voltage (J–V), and external quantum efficiency (EQE). A Schottky junction, of about 180 nm in width, was formed at the front TCO contact, resulting in an EQE of approximately 70% in the short-wavelength region. The champion device reached 3.8% AM1.5 in power conversion efficiency, and retained efficiency over several weeks of air-exposure. A record open-circuit voltage (VOC) of 0.75 V was achieved by employing PbS CQDs of 1.56 eV in the bandgap. Advantages including the simple device structure, efficient carrier extraction, and air-stability demonstrated in this study suggest that inverted Schottky CQD SCs can reduce the price per Watt ratio and facilitate the development of CQD tandem solar cells.