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Impact of Marginal Exciton-Charge-Transfer State Offset on Charge Generation and Recombination in Polymer:Fullerene Solar Cells

Vezie, MS; Azzouzi, M; Telford, AM; Hopper, TR; Sieval, AB; Hummelen, JC; Fallon, K; ... Nelson, J; + view all (2019) Impact of Marginal Exciton-Charge-Transfer State Offset on Charge Generation and Recombination in Polymer:Fullerene Solar Cells. ACS Energy Letters , 4 (9) pp. 2096-2103. 10.1021/acsenergylett.9b01368. Green open access

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Abstract

The energetic offset between the initial photoexcited state and charge-transfer (CT) state in organic heterojunction solar cells influences both charge generation and open-circuit voltage (Voc). Here, we use time-resolved spectroscopy and voltage loss measurements to analyze the effect of the exciton–CT state offset on charge transfer, separation, and recombination processes in blends of a low-band-gap polymer (INDT-S) with fullerene derivatives of different electron affinity (PCBM and KL). For the lower exciton–CT state offset blend (INDT-S:PCBM), both photocurrent generation and nonradiative voltage losses are lower. The INDT-S:PCBM blend shows different excited-state dynamics depending on whether the donor or acceptor is photoexcited. Surprisingly, the charge recombination dynamics in INDT-S:PCBM are distinctly faster than those in INDT-S:KL upon excitation of the donor. We reconcile these observations using a kinetic model and by considering hybridization between the lowest excitonic and CT states. The modeling results show that this hybridization can significantly reduce Voc losses while still allowing reasonable charge generation efficiency.

Type: Article
Title: Impact of Marginal Exciton-Charge-Transfer State Offset on Charge Generation and Recombination in Polymer:Fullerene Solar Cells
Open access status: An open access version is available from UCL Discovery
DOI: 10.1021/acsenergylett.9b01368
Publisher version: https://doi.org/10.1021/acsenergylett.9b01368
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10084841
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