Dam, Henrik Friis3; Holmes, Natalie P.4; Andersen, Thomas Rieks5; Larsen-Olsen, Thue Trofod1; Barr, Matthew4; Kilcoyne, A. L. David7; Zhou, Xiaojing4; Dastoor, Paul C.4; Krebs, Frederik C1; Belcher, Warwick J.4
1 Department of Energy Conversion and Storage, Technical University of Denmark2 Functional organic materials, Department of Energy Conversion and Storage, Technical University of Denmark3 Department of Micro- and Nanotechnology, Technical University of Denmark4 University of Newcastle5 Risø National Laboratory for Sustainable Energy, Technical University of Denmark6 Lawrence Berkeley National Laboratory7 Lawrence Berkeley National Laboratory
Scanning transmission X-ray microscopy (STXM) compositional mapping has been used to probe the mesomorphology of nanoparticles (NPs) synthesized from two very different polymer:fullerene blends: poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) and poly[4,8-bis(2-ethylhexyloxy)benzo(1,2-b:4,5-b')dithiophene-alt-5, 6-bis(octyloxy)-4,7-di(thiophen-2-yl)(2,1,3-benzothiadiazole)-5,5'-diyl] (PSBTBT): PCBM. The STXM data shows that both blends form core-shell NP structures with similar shell compositions, but with different polymer:fullerene ratios in the core regions. P3HT:PCBM and PSBTBT:PCBM NP organic photovoltaic (OPV) devices have been fabricated and exhibit similar device efficiencies, despite the PSBTBT being a much higher performing low band gap material. By comparing the measured NP shell and core compositions with the optimized bulk hetero-junction (BHJ) compositions, we show that the relatively higher performance of the P3HT:PCBM NP device arises from the fact that its shell composition is much closer to the optimal BHJ value than that of the PSBTBT:PCBM NP device. [All rights reserved Elsevier].
Solar Energy Materials and Solar Cells, 2015, Vol 138, p. 102-108