From Event: SPIE Organic Photonics + Electronics, 2017
Intrinsic photodegradation of organic solar cells, theoretically attributed to C-H bond rearrangement/breaking, remains a key commercialization barrier. This work presents, via dark electron paramagnetic resonance (EPR), the first experimental evidence for metastable C dangling bonds (DBs) formed by blue/UV irradiation of polymer:fullerene blend films in nitrogen. The DB density increased with irradiation and decreased ~4 fold after 2 weeks in the dark. The dark EPR also shows increased densities of other spin-active sites in photodegraded polymer, fullerene, and polymer:fullerene blend films, consistent with broad electronic measurements of fundamental properties, including defect/gap state densities. The EPR and electronic measurements enable identification of defect states, whether in the polymer, fullerene, or at the donor/acceptor (D/A) interface. Importantly, the EPR results indicate that the DBs are at the D/A interface, as they were present only in the blend films. The role of polarons in interface DB formation will also be discussed.
Fadzai Fungura, William Robin Lindemann, Joseph Shinar, and Ruth Shinar, "Carbon dangling bonds in photodegraded polymer:fullerene solar cells (Conference Presentation)," Proc. SPIE 10363, Organic, Hybrid, and Perovskite Photovoltaics XVIII, 103631B (Presented at SPIE Organic Photonics + Electronics: August 10, 2017; Published: 19 September 2017); https://doi.org/10.1117/12.2275054.5581136171001.
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