Carbon Dangling Bonds in Photodegraded Polymer:Fullerene Solar Cells |
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| Authors: | Fadzai Fungura William R Lindemann Joseph Shinar Ruth Shinar |
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| Institution: | 1. Ames Laboratory, USDOE, Microelectronics Research Center, and Physics & Astronomy Department, Iowa State University, Ames, IA, USA;2. Ames Laboratory, USDOE and Materials Science & Engineering Department, Iowa State University, Ames, IA, USA;3. Ames Laboratory, USDOE and Physics & Astronomy Department, Iowa State University, Ames, IA, USA;4. Microelectronics Research Center and Electrical & Computer Engineering Department, Iowa State University, Ames, IA, USA |
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| Abstract: | 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 increases with irradiation and decreases ≈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 is also discussed. |
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| Keywords: | carbon dangling bonds efficient low‐gap polymer:fullerene bulk heterojunction solar cells EPR of carbon dangling bonds photodegradation of organic bulk heterojunction photovoltaic cells photogeneration of carbon dangling bonds at polymer:fullerene interface |
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