Abstract
The lack of viable solid-state annihilators is one of the greatest hurdles in perovskite-sensitized triplet-triplet annihilation upconversion (UC). Unfavorable singlet and triplet energy surfaces in the solid state have limited the successful implementation of many conventional solution-based annihilators. To date, rubrene is still the best-performing annihilator; however, this comes at the cost of a limited apparent anti-Stokes shift. To this point, anthracene derivatives are promising candidates to increase the apparent anti-Stokes shift. The well-known green glowstick dye 9,10-(bisphenylethynyl)anthracene (BPEA) and its chlorinated derivatives have already shown promise in solution-based UC applications. Due to favorable band alignment of the perovskite and triplet energy levels of BPEA, it is conceivable that a wide variety of BPEA derivatives can be compatible with the perovskite-based UC system. Here, the properties of the parent molecule BPEA and its derivatives 1-chloro-9,10-(bisphenylethynyl)anthracene and 2-chloro-9,10-(bisphenylethynyl)anthracene are investigated. Despite similar optical properties in solution, the different molecules exhibit vastly different properties in thin films. UC studies in lead halide perovskite/BPEA bilayer devices demonstrate the importance of intermolecular coupling on the resulting properties of the upconverted emission.