jz300710a_si_001.pdf (514.41 kB)
Enhanced Vertical Concentration Gradient in Rubbed P3HT:PCBM Graded Bilayer Solar Cells
journal contribution
posted on 2015-12-16, 21:33 authored by Varun Vohra, Gianmichele Arrighetti, Luisa Barba, Koichi Higashimine, William Porzio, Hideyuki MurataGraded bilayer solar cells have proven to be at least
as efficient
as the bulk heterojunctions when it comes to the Poly(3-hexylthiophene)
(P3HT) - [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) donor–acceptor
system. However, control of the vertical concentration gradient using
simple techniques has never been reported. We demonstrate that rubbing
the P3HT layer prior to PCBM deposition induces major morphological
changes in the active layer. Using the newly introduced energy-dispersive
X-ray spectroscopy element mapping technique, we found that rubbing
P3HT induces the formation of an ideal vertical donor–acceptor
concentration gradient. Furthermore, the P3HT crystallites undergo
a molecular reorientation from edge-on to face-on configuration inducing
a better charge transport in the vertical direction. The combination
of these two major morphological changes leads to the fabrication
of high-performance solar cells that exhibit, to date, the record
efficiencies for spin-coated graded bilayers solar cells.