Abstract
Understanding the factors affecting energy loss in organic photovoltaics (OPVs) is imperative to achieve further improvements in their efficiency and to establish design rules for the development of new materials. Here, we provide direct experimental evidence supporting correlation between charge-transfer (CT) state static disorder and energy loss. Specifically, upon studying several planar and bulk heterojunction solar cells, we demonstrate that the non-radiative energy loss component quadratically increases with increasing Gaussian CT-state disorder. We also show that by defining the total energy loss in terms of the peak of the CT-state distribution, obtained from temperature-dependent external quantum efficiency measurements, the effect of disorder on OPV performance can be unambiguously identified, offering a universal metric for quantifying energy loss across various devices.
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•Correlation between non-radiative energy loss and CT-state energetic disorder•D-A interface optimization strategy for reduced non-radiative energy loss•Universal energy loss metric incorporating disorder
Organic photovoltaics (OPVs) incur considerably higher total energy loss compared with inorganic devices, which often amounts to ∼0.6 eV, regardless of the degree of disorder at the donor-acceptor (D-A) interface; quite counter-intuitive, considering the crucial role the charge-transfer (CT) state energetic distribution plays in energy loss processes. In this work, we experimentally show that non-radiative energy loss quadratically depends on the CT-state energetic disorder, and incorporation of this contribution shifts the total energy loss from the constant ∼0.6 eV to values that scale with increasing disorder. This reveals the importance of morphological optimization of the D-A ensemble to ensure minimal CT-state energetic variation and enables direct comparison of device performances across various material systems and processing conditions. Ultimately, our findings open the door to establish new design rules toward achieving the full thermodynamic potential of OPVs.
Experimental data reveal a strong correlation between the non-radiative energy loss and charge-transfer (CT) state energetic disorder of organic photovoltaic (OPV) devices. Defining total energy loss in terms of the peak of the CT-state distribution showcases the effect of energetic disorder on OPV performance across a broad range of devices and offers valuable insight into designing the ideal donor-acceptor interface for reduced energy loss.