Carrier Dynamics in Upconverting Thin Film Perovskite/Rubrene Bilayers Studied by Combined Surface Photovoltage and Photoluminescence

A typical perovskite-driven photon upconverter consists of lead halide perovskite thin film layered with a small molecule semiconductor annihilator, such as rubrene. These systems exhibit triplet-triplet annihilation upconversion from the near-infrared to the visible spectrum, with the perovskite film acting as a triplet sensitizer while the rubrene layer functions as the annihilator and emitter [1, 2]. A key feature of this style of upconverter, which removes the conventional excitonic triplet sensitizer and replaces it with the interface of a bulk semiconductor film, is the conversion of free electrons and holes in the perovskite into strongly-bound electron-hole pairs (i.e. excitons) within the organic annihilator film. The process is an emerging application of lead halide perovskite beyond the photovoltaics space, and is interesting both in a photonics role, and as a fundamental investigation into energy transduction at hybrid semiconductor interfaces. This study aims to generate new insights into these perovskite upconverter systems using a combination of transient surface photovoltage and photoluminescence methods. Transient surface photovoltage measures the transient electrical polarization across a semiconductor film stack resulting from carrier diffusion, trapping and recombination following excitation by a short laser pulse. As such, it offers insight into the net charge distribution throughout the sample as well as the rates of various carrier transfer and recombination processes. Photoluminescence,