Photon Upconverting Solid Films with Improved Efficiency for Endowing Perovskite Solar Cells with Near-Infrared Sensitivity

Perovskite solar cells have emerged as the next-generation high-efficiency solar cell, but their absorption is mostly limited to the visible (vis) range. One possible solution is to integrate near-infrared (NIR)-to-vis photon upconversion (UC). Herein, we show the first example of endowing perovskite solar cells with NIR sensitivity by using solid films showing NIR-to-vis UC based on triplet-triplet annihilation (TTA). A high TTA-UC efficiency of 4.1 +/- 0.3% at an excitation intensity of 125 W/cm(2) is achieved by sensitizing a rubrene (acceptor) triplet with an osmium (Os) complex donor having singlet-to-triplet (S-T) absorption in the NIR range, and by increasing the fluorescence quantum yield through energy harvesting to a highly fluorescent collector. In particular, our spectroscopic studies indicate that the upconverted acceptor singlet energy is almost selectively transferred to the collector rather than being quenched by the donor. By attaching the TTA-UC film behind a semi-transparent perovskite solar cell, a photocurrent generation is observed under excitation at 938 nm.