Carbon Dangling Bonds in Photodegraded Polymer:Fullerene Solar Cells. Issue 6 (21st November 2016)

• Record Type: Journal Article
• Authors: Fungura, Fadzai; Lindemann, William R.; Shinar, Joseph; Shinar, Ruth
• Is Part Of: Advanced energy materials. Volume 7:Issue 6(2017)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2016-11-21
• Subjects: 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; Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.201601420
• Languages: English
• ISSNs: 1614-6832

Abstract

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. Abstract : For the first time, strong electron paramagnetic resonance evidence is provided that irradiation of bulk heterojunction polymer:fullerene solar cells by blue and shorter wavelength photons (<495 nm), likely assisted by highly energized ("hot") polarons, generates C dangling bonds at the polymer:fullerene interfaces. This photodegradation process may be one of the key obstacles to commercialization of such cells.