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Organic and perovskites photovoltaic devices have many advantageous properties including tailorable light absorption, low embodied energy manufacturing, structural conformality, and low material toxicity. Apart from solar cells, these properties also make these materials attractive for applications such as indoor light-harvesting cells and photodetectors. A critical parameter limiting the performance of these diode devices is the dark saturation current which limits the open-circuit voltage of organic solar cells and the detectivity of organic photodetectors. It is known that the dark saturation current is strongly limited by non-radiative processes resulting in dark saturation currents orders of magnitude higher than expected for radiative band-to-band transitions; however, the origin of these non-radiative processes is still debated. Here, we show that the dark saturation current in organics is fundamentally mediated by mid-gap trap states.[1,2] This midgap traps are also present in perovskites and impose additional voltage loss which can reduced upon passivation.[3] This new insight is generated by a universal trend observed for a large set of organic bulk heterojunction systems and substantiated by sensitive external quantum efficiency and temperature-dependent current measurements.[4] These findings have important implications for organics and perovskites, providing new insight into the origin of non-radiative losses in light-harvesting applications such as organic and perovskite solar cells and photodiodes.
References:
1. Sandberg, Oskar J., Armin, Ardalan, et al. "Mid-gap trap state-mediated dark current in organic photodiodes." Nature Photonics (2023): 1-7.
2. Zarrabi, Nasim; Armin, Ardalan et al. "Charge-generating mid-gap trap states define the thermodynamic limit of organic photovoltaic devices." Nature Communications 11.1 (2020): 5567.
3. Warby, Jonathan; Stolterfoht, Martin; Armin, Ardalan et al. "Understanding performance limiting interfacial recombination in pin perovskite solar cells." Advanced Energy Materials 12.12 (2022): 2103567.
4. Zarrabi, Nasim; Armin. Ardalan et al. "Subgap Absorption in Organic Semiconductors." The Journal of Physical Chemistry Letters 14 (2023): 3174-3185.
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