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A Multi-modal Approach to Understanding Degradation of Organic Photovoltaic Materials
journal contributionposted on 2021-09-08, 21:36 authored by Michael A. Anderson, Bryon W. Larson, Erin L. Ratcliff
State-of-the-art organic photovoltaic (OPV) materials are composed of complex, chemically diverse polymeric and molecular structures that form highly intricate solid-state interactions, collectively yielding exceptional tunability in performance and aesthetics. These properties are especially attractive for semitransparent power-generating windows or shades in living environments, greenhouses, or other architectural integrations. However, before such a future is realized, a broader and deeper understanding of property stability must be acquired. Stability during operating and environmental conditions is critical, namely, material color steadfastness, optoelectronic performance retention, morphological rigidity, and chemical robustness. To date, no single investigation encompasses all four distinct, yet interconnected, metrics. Here, we present a multimodal strategy that captures a dynamic and interconnected evolution of each property during the course of an accelerated photobleaching experiment. We demonstrate this approach across relevant length scales (from molecular to visual macroscale) using X-ray photoelectron spectroscopy, grazing-incidence X-ray scattering, microwave conductivity, and time-dependent photobleaching spectroscopies for two high-performance semitransparent OPV blendsPDPP4T:PC60BM and PDPP4T:IEICO-4F, with comparisons to the stabilities of the individual components. We present direct evidence that specific molecular acceptor (fullerene vs nonfullerene) designs and the resulting donor–acceptor interactions lead to distinctly different mechanistic routes that ultimately arrive at what is termed “OPV degradation.” We directly observe a chemical oxidation of the cyano endcaps of the IEICO-4F that coincides with a morphological change and large loss in photoconductivity while the fullerene acceptor-containing blend demonstrates a significantly greater fraction of oxygen uptake but retains 55% of the photoconductivity. This experimental roadmap provides meaningful guidance for future high-throughput, multimodal studies, benchmarking the sensitivity of the different analytical techniques for assessing stability in printable active layers, independent of complete device architectures.
single investigation encompassessignificantly greater fractionprintable active layersmaterial color steadfastnessdifferent analytical techniquesdependent photobleaching spectroscopiescontaining blend demonstratescomplete device architectureschemically diverse polymericart organic photovoltaicaccelerated photobleaching experimentray photoelectron spectroscopyfullerene vs nonfullerenepresent direct evidenceoptoelectronic performance retention60 subspecific molecular acceptorproperty stability mustfullerene acceptorray scatteringyet interconnectedvisual macroscaleusing xunderstanding degradationultimately arrivetwo highstate interactionssemitransparent powerretains 55oxygen uptakemultimodal studiesmultimodal strategymorphological rigiditymorphological changemolecular structuresmodal approachmicrowave conductivityliving environmentslarge lossinterconnected evolutionindividual componentsincidence xgenerating windowsfour distinctespecially attractiveenvironmental conditionsdirectly observedeeper understandingcyano endcapschemical robustnesschemical oxidationassessing stabilityarchitectural integrations