title: Reducing optical losses in organic solar cells using microlens arrays: theoretical and experimental investigation of microlens dimensions.
abstract: The performance of organic photovoltaic devices is improving steadily and efficiencies have now exceeded 10%. However, the incident solar spectrum still largely remains poorly absorbed. To reduce optical losses, we employed a microlens array (MLA) layer on the side of the glass substrate facing the incident light; this approach does not interfere with the processing of the active-layer. We observed up to 10% enhancement in the short circuit current of poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl}):(6,6)-phenyl C71-butyric acid methyl ester (PTB7:PC71BM) OPV cells. Theoretically and experimentally investigating several MLA dimensions, we found that photocurrent increases with the ratio of the height to the pitch size of MLA. Simulations reveal the enhancement mechanisms: MLA focuses light, and also increases the light path within the active-layer by diffraction. Photocurrent enhancements increase for a polymer system with thinner active-layers, as demonstrated in poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT):PC71BM OPVs with 17% improvement in short circuit current.
authors.affiliation: Department of Electrical and Computer Engineering, Iowa State University, Ames, Iowa 50011, USA. sumitc@iastate.edu.
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Chen
authors.forename: Moneim
authors.initials: M
authors.lastname: Elshobaki
authors.forename: Ryan
authors.initials: R
authors.lastname: Gebhardt
authors.forename: Stephen
authors.initials: S
authors.lastname: Bergeson
authors.forename: Max
authors.initials: M
authors.lastname: Noack
authors.forename: Joong-Mok
authors.initials: JM
authors.lastname: Park
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Hillier
authors.forename: Kai-Ming
authors.initials: KM
authors.lastname: Ho
authors.forename: Rana
authors.initials: R
authors.lastname: Biswas
authors.forename: Sumit
authors.initials: S
authors.lastname: Chaudhary