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Photoinduced Electron-Transfer Distance Is Controlled by the Driving Force in Solid-State Organic Donor-Acceptor Systems

Journal Article · · Nature Chemistry
Understanding how short-range electron transfer generates photocurrent in organic solar cells and what photochemical driving force is needed to maximize efficiencies has been an immensely difficult problem. Here we show how these questions are intertwined: the driving force controls the average charge-transfer distance, skipping the shortest-range states in the optimal case. Using photoinduced absorption-detected magnetic resonance, we measure average charge-separation distances in dilute donor–acceptor blends as a function of driving force, and compare these with free charge yields measured by time-resolved microwave conductivity. We find that the largest driving forces show the shortest charge-separation distances, explaining their suppressed free-carrier generation. These results support a long-range electron-transfer model, wherein the driving force controls the initial delocalization of the electron–hole pair. The minimum driving force required for efficient charge separation (and minimal voltage losses) is ultimately set by the dielectric constant of the material.
Research Organization:
National Laboratory of the Rockies (NLR), Golden, CO (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division
DOE Contract Number:
AC36-08GO28308;
OSTI ID:
3029859
Report Number(s):
NLR/JA-5900-91756
Journal Information:
Nature Chemistry, Journal Name: Nature Chemistry
Country of Publication:
United States
Language:
English