Oxygen-dependent photophysics and photochemistry of prototypical compounds for organic photovoltaics: inhibiting degradation initiated by singlet oxygen at a molecular level

Abstract

Photo-initiated, oxygen-mediated degradation of the molecules in the active layer of organic photovoltaic, OPV, devices currently limits advances in the development of solar cells. To address this problem systematically and at a molecular level, it is informative to quantify the kinetics of the pertinent processes, both in solution phase and in solid films. To this end, we examined the oxygen-dependent photophysics and photochemistry of selected functionalized fullerenes, thiophene derivatives, and a subphthalocyanine commonly used in OPV devices. We find that the photosensitized production of singlet molecular oxygen, O2(a1Δg), by these molecules is a key step in the degradation process. We demonstrate that the addition of either β-carotene or astaxanthin as antioxidants can inhibit degradation by a combination of three processes: (a) deactivation of O2(a1Δg) to the oxygen ground state, O2(X3Σg−), (b) quenching of the O2(a1Δg) precursor, and (c) sacrificial reactions of the carotenoid with free radicals formed in the photo-initiated reactions. For OPV systems in which reaction with O2(a1Δg) contributes to the degradation, the first two of these processes are desired and should have appreciable impact in prolonging the longevity of OPV devices because they do not result in a chemical change of the system.

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

“… 926 − 928 Other stabilizes (e.g., carotene) 929 chemically react with 1 O 2 and thus are consumed. Other donors that can decompose 1 O 2 include certain sulfur compounds, 930 astaxanthin, 931 allylurea, 932 azides. 933 , 934 Molecules where a reducing and an oxidizing moiety are covalently linked have been reported.…”

Recent Progress and Challenges toward Highly Stable Nonfullerene Acceptor‐Based Organic Solar Cells

“…It is found that the photooxidation process can be mediated by the triplet exciton kinetics with the formation of singlet oxygen, which has been well studied for fullerene and polymer donors. [ 177 178 ] For example, the PCBM triplets can be formed via intersystem crossing from the PCBM singlet state after the absorption of photons, and these triplet states can be quenched by molecular oxygen to generate highly reactive singlet oxygen. [ 179 ] While the triplet‐mediated photooxidation study of NFA is limited, Y6 is found to be a triplet acceptor and therefore may suffer from severe photooxidation process in air.…”

“…The use of stabilizers such as antioxidizing agents to regulate the detrimental chemical reactions and inhibit the photooxidation of the photoactive materials may be a promising strategy to enhance the stability of NFA OSCs, considering the successful application of several stabilizers in biology, perovskite solar cells (PSCs), and polymer:fullerene OSCs. [ 178,225–228 ] For example, the inexpensive natural antioxidants uric acid, [ 229 ] tea polyphenol, [ 230 ] and ascorbic acid [ 231 ] have been used in tin‐based PSCs to prevent the oxidation Sn 2+ , thereby resulting in significantly improved device stability. It has been found that a set of structurally varied hindered phenols can stabilize the lifetime of P3HT:PCBM devices without compromising their performance, owing to the hydrogen donation and radical scavenging properties of hindered phenols which can significantly reduce the radicals within the photoactive layer.…”

New Approach in the Application of Conjugated Polymers: The Light-Activated Source of Versatile Singlet Oxygen Molecule

“…Since the pioneering work on conductive polyacetylene by MacDiarmid, Heeger, and Shirakawa [23], CPs have been mainly investigated for the application in organic electronics-e.g., in organic photovoltaics (OPVs), organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), (bio)sensors, or batteries [24][25][26]. The formation of various ROS by conjugated polymers have been known for several years [27]; however, this phenomenon is rather undesirable in the key application of conducting polymers, organic electronics, since it may lead to the oxidative decomposition of the electroactive materials, and thus results in the lowering of the efficiency of the device [28][29][30][31]. Still, what is unfavorable for organic electronic devices appears to be attractive for the biological or photocatalytic applications.…”