Triplet-Sensitization by Lead Halide Perovskite Thin Films for Near-Infrared-to-Visible Upconversion

Abstract

Lead halide-based perovskite thin films have attracted great attention due to the rapid increase in perovskite solar cell efficiencies. The same optoelectronic properties that make perovskites ideal absorber materials in solar cells are also beneficial in other light-harvesting applications and make them prime candidates as triplet sensitizers in upconversion via triplet-triplet annihilation in rubrene. In this contribution, we take advantage of long carrier lifetimes and carrier diffusion lengths in perovskite thin films, their high absorption cross-sections throughout the visible spectrum, and the strong spin-orbit coupling owing to the abundance of heavy atoms to sensitize the upconverter rubrene. Employing bulk perovskite thin films as the absorber layer and spin-mixer in inorganic/organic heterojunction upconversion devices allows us to forego the passivating ligands required for colloidal sensitizers, which can hinder exciton transport through large scale arrays and reduce the triplet transfer efficiency to the annihilator. Our bilayer device exhibits an upconversion efficiency in excess of 3% under 785 nm illumination at an incident power of ∼88 W/cm[superscript 2]. Keywords: lead halide perovskites; upconversion; free carriers; triplet excitons; charge-separated state; triplet-charge annihilation; triplet-triplet annihilation