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Relating Frontier Orbital Energies from Voltammetry and Photoelectron Spectroscopy to the Open‐Circuit Voltage of Organic Solar Cells
Author(s) -
Willems Robin E. M.,
Weijtens Christ H. L.,
Vries Xander,
Coehoorn Reinder,
Janssen René A. J.
Publication year - 2019
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201803677
Subject(s) - materials science , homo/lumo , x ray photoelectron spectroscopy , ultraviolet photoelectron spectroscopy , open circuit voltage , ionization energy , density functional theory , molecular orbital , analytical chemistry (journal) , polymer solar cell , organic solar cell , acceptor , cyclic voltammetry , chemistry , polymer , ionization , solar cell , computational chemistry , voltage , electrochemistry , electrode , molecule , physics , organic chemistry , optoelectronics , condensed matter physics , nuclear magnetic resonance , composite material , quantum mechanics , ion
For 19 diketopyrrolopyrrole polymers, the highest occupied molecular orbital (HOMO) energies are determined from i) the oxidation potential with square‐wave voltammetry (SWV), ii) the ionization potential using ultraviolet photoelectron spectroscopy (UPS), and iii) density functional theory (DFT) calculations. The SWV HOMO energies show an excellent linear correlation with the open‐circuit voltage ( V oc ) of optimized solar cells in which the polymers form blends with a fullerene acceptor ([6,6]‐phenyl‐C 61 ‐butyl acid methyl ester or [6,6]‐phenyl‐C 71 ‐butyl acid methyl ester). Remarkably, the slope of the best linear fit is 0.75 ± 0.04, i.e., significantly less than unity. A weaker correlation with V oc is found for the HOMO energies obtained from UPS and DFT. Within the experimental error, the SWV and UPS data are correlated with a slope close to unity. The results show that electrochemically determined oxidation potentials provide an excellent method for predicting the V oc of bulk heterojunction solar cells, with absolute deviations less than 0.1 V.