J. Feenstra, M. van Eerden, A.K. Lemmens, W. de Poel, P.H.J. Kouwer, A.E. Rowan, J. Schermer,
Muscovite mica as a growth template of PC₆₁BM crystallites for organic photovoltaics,
Cryst. Eng. Comm. 19 (2017) 4424-4436

Abstract
Controlling the microscopic organization of active components is crucial for the performance of organic photovoltaic (OPV) cells. In this work, (001) muscovite mica was used as a growth template to study the formation of PC₆₁BM crystallites in the active layer structure of OPV cells. The structures were spin-coated from a PC₆₁BM : P3HT solution and subsequently annealed. The parameter range to produce layers with high surface density of (sub)micrometer sized PC₆₁BM crystallites was significantly larger for mica than for other substrates. The enhanced PC₆₁BM nucleation is attributed to an epitaxial relation between the mica surface and PC₆₁BM, which was found to crystallise in a hexagonal crystal structure. Through a float-off procedure, the active layer was transferred from the mica substrate to a conductive substrate, which formed the basis of the transferred inverted solar cell. A power conversion efficiency of 2.1% was obtained for this transferred device, which with a 22% higher short-circuit current density outperforms its conventional counterpart that was directly produced on the conductive substrate. A set-up for simultaneous laser beam induced current (LBIC) and surface reflection analysis revealed that the increased current density originates from large circular areas with a radius of about 10 μm around the PC₆₁BM crystallites.