Temperature-Dependent Charge-Transfer-State Absorption and Emission Reveal the Dominant Role of Dynamic Disorder in Organic Solar Cells

The energetic landscape of charge transfer (CT) states at the interface electron donating and accepting domains in organic optoelectronic devices is crucial for their performance. Central questions -- such as role static disorder vibrational effects are under ongoing dispute. This study provides an in-depth analysis temperature dependent broadening spectroscopic absorption emission features CT with small molecule-fullerene blends. We confirm validity electro-optical reciprocity relation between photovoltaic external quantum efficiency ($\mathrm{EQE_{PV}}$) electroluminescence ($\mathrm{EQE_{EL}}$), enabling us to validate device during experiment. validated allows fit our experimental data several models, compare extracted state energies corresponding open circuit voltage limit $0\mathrm{\,K}$. Our findings unveil that characteristics usually not symmetric, dominated by temperature-activated (vibrational) instead disorder.