Influence of Disorder and State Filling on Charge-Transfer-State Absorption and Emission Spectra

Characterizing the energetic disorder of the charge-transfer (CT) state is crucial to understanding organic photovoltaic devices, but is complicated by the discrepancy between temperature-dependent absorption and emission spectra. The authors show that, unlike absorption measurements, electroluminescence measurements do n00exo00ext reveal the full extent of the CT-state distribution at low temperatures. In a highly disordered blend, CT-state filling is incomplete, and injected carriers do not reach equilibrium sites before recombining. CT disorder c00exa00exn be reliably found from temperature-dependent measurements of external quantum efficiency, which can distinguish dynamic from static disorder.