Impact of marginal exciton–charge-transfer state offset on charge generation and recombination in polymer:fullerene solar cells
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Accepted version
Author(s)
Type
Journal Article
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.
Date Issued
2019-09-13
Date Acceptance
2019-08-05
Citation
ACS Energy Letters, 2019, 4 (9), pp.2096-2103
ISSN
2380-8195
Publisher
American Chemical Society (ACS)
Start Page
2096
End Page
2103
Journal / Book Title
ACS Energy Letters
Volume
4
Issue
9
Copyright Statement
© 2019 American Chemical Society.
Sponsor
Engineering and Physical Sciences Research Council
The Royal Society
Engineering & Physical Science Research Council (EPSRC)
Engineering & Physical Science Research Council (EPSRC)
Grant Number
UF130178
EP/M025020/1
EP/P005543/1
Subjects
Science & Technology
Physical Sciences
Technology
Chemistry, Physical
Electrochemistry
Energy & Fuels
Nanoscience & Nanotechnology
Materials Science, Multidisciplinary
Chemistry
Science & Technology - Other Topics
Materials Science
QUANTUM EFFICIENCY
ABSORPTION
SEPARATION
ENERGY
GAP
DISSOCIATION
DYNAMICS
Publication Status
Published
Date Publish Online
2019-08-06