Search for: All records

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. 

Abstract Triplet–triplet annihilation‐based photon upconversion (TTA‐UC) can efficiently generate higher energy photons at low relative fluences. Bulk metal halide perovskites have offered promise in efficiently sensitizing molecular triplet states in the solid state, necessary for the integration of TTA‐UC into device‐based applications. Recent work focused on TTA‐UC from a rubrene triplet annihilator sensitized by perovskite thin films has established relatively efficient charge extraction from the perovskite, forming the triplet exciton in rubrene. Yet, the specifics underpinning charge transfer at the perovskite/rubrene interface are not fully elucidated. To improve device performance and study the properties governing charge transfer at the interface, various organic solvents are explored to treat the perovskite surface. Scanning tunneling microscopy and spectroscopy show a difference in the electronic band structure, where both n‐ and p‐type terminated perovskite surfaces are observed depending on the solvent used. Supported by optical spectroscopy, the impact of the perovskite electronic structure is monitored, indicating that n‐type perovskite sensitizers feature higher TTA‐UC efficiencies due to favorable band bending resulting in efficient hole‐mediated triplet formation. Overall, the tuning of the electronic structure of the perovskite sensitizer through solvent treatment is shown to be a key force in tuning the mechanism of efficient triplet generation.