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Ultrafast Polaron-Pair Dynamics in a poly(3-hexylthiophene-2,5-diyl) Device Influenced by a Static Electric Field: Insights Into Electric-Field-Related Charge Loss

Ultrafast Polaron-Pair Dynamics in a poly(3-hexylthiophene-2,5-diyl) Device Influenced by a Static Electric Field: Insights Into Electric-Field-Related Charge Loss

Debkumar Rana, Patrice Donfack, Vladislav Jovanov, Veit Wagner, Arnulf Materny

Phys Chem Chem Phys. 2019 Oct 14;21(38):21236-21248.

PMID: 31532418

Abstract:

The generation and decay mechanisms of polaron pairs in organic semiconductor-based optoelectronic devices under operational conditions are relevant for a better understanding of photophysical processes affecting the device performance, since the possible occurrence of a polaron pair introduces an intermediate step in exciton dissociation into fully separated charge carriers. The role played by static electric fields in polaron-pair dynamics is important but poorly understood or not investigated in detail. In this work, insights into the polaron-pair dynamics in neat poly(3-hexylthiophene-2,5-diyl) (P3HT) thin films and P3HT films sandwiched between electrical contacts with an applied external static electric field are probed using femtosecond pump-probe transient absorption spectroscopy. Asymmetric contacts result in P3HT devices with application-related diode characteristics. Consistent with the electric field-induced dissociation of oppositely charged species, we show that polaron-pair dissociation into charge carriers occurs in the P3HT device more significantly with increasing reverse bias, and that this process follows an initial instantaneous polaron-pair photoabsorption quenching due to a pronounced immediate loss of primary photoexcitation species (hot excitons). Furthermore, we show that the net-electric field present in the P3HT diode (including built-in-potential at 0 V bias) results in a more complex dynamics with new findings as compared to the neat-P3HT thin film case. Indeed, besides polaron pairs directly originating from hot excitons, we experimentally observe polaron-pair formation during exciton dissociation via a field-mediated generation process, resulting in a slower contribution to the overall decay dynamics. Moreover, unlike in the external electric field-free P3HT film, bimolecular annihilation processes clearly appear as an additional loss channel when a field is applied and hence have an impact on carrier generation performance in a working device.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP156074985	Poly(3-hexylthiophene-2,5-diyl)		156074-98-5	Price

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