title: Design considerations for electrode buffer layer materials in polymer solar cells.
abstract: Electrode buffer layers in polymer-based photovoltaic devices enable highly efficient devices. In the absence of buffer layers, we show that diode rectification is lost in ITO/P3HT:PCBM/Ag (ITO = indium tin oxide; P3HT = poly(3-hexylthiophene); PCBM = phenyl C61-butyric acid methyl ester) devices due to nonselective charge injection through the percolated phase pathways of a bulk heterojunction active layer. Charge-selective injection, and thus rectification and device function, can be regained by placing thin, polymeric buffer layers that break the direct electrode-active layer contact. Additionally, we show that strong active layer-buffer layer interactions lead to unwanted vertical phase separation and a kinked current-voltage curve. Device function is regained, increasing power conversion efficiency from 3.6% to 7.2%, by placing a noninteracting layer between the buffer and active layer. These results guide the design and selection of future polymeric electrode buffer layers for efficient polymer solar cell devices.
authors.affiliation: Materials Science and Engineering, ‡Macromolecular Science and Engineering, and ∥Chemical Engineering, University of Michigan , Ann Arbor, 48109, United States.
authors.forename: David
authors.initials: D
authors.lastname: Bilby
authors.forename: Bradley
authors.initials: B
authors.lastname: Frieberg
authors.forename: Shobhita
authors.initials: S
authors.lastname: Kramadhati
authors.forename: Peter
authors.initials: P
authors.lastname: Green
authors.forename: Jinsang
authors.initials: J
authors.lastname: Kim
keywords: electrode interface; polymer photovoltaic