title: Indium tin oxide-free tandem polymer solar cells on opaque substrates with top illumination.
abstract: Top-illuminated, indium tin oxide (ITO)-free, tandem polymer solar cells are fabricated on opaque substrates in an inverted device configuration. In the tandem cell, a wide band gap subcell, consisting of poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) blended with [70]PCBM is combined with a small band gap subcell consisting of a mixture of poly[{2,5-bis(2-hexyldecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl}-alt-{[2,2'-(1,4-phenylene)bisthiophene]-5,5'-diyl}] (PDPPTPT) and [60]PCBM. Compared to the more common bottom-illuminated inverted tandem polymer solar cells on transparent ITO substrates, the front and back cells must be reversed when using opaque substrates and a transparent and conductive top contact must be employed to enable top illumination. A high conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer in combination with Ag lines surrounding the active area as current collection electrode is used for this purpose. The tandem polymer solar cell on an opaque glass/metal substrate yields a power conversion efficiency of 6.1% when the thicknesses of the photoactive layers are balanced for optimum performance. This is similar to the equivalent inverted tandem device fabricated on a transparent glass/ITO substrate.
authors: Materials innovation institute (M2i) , 2600 GA Delft, Netherlands.
authors: Dhritiman
authors: D
authors: Gupta
authors: Martijn M
authors: MM
authors: Wienk
authors: René A J
authors: RA
authors: Janssen