Embedding a Diketopyrrolopyrrole-Based Crosslinking Interfacial Layer Enhances the Performance of Organic Photovoltaics.

In this study, we prepared DPPBTDA, a diketopyrrolopyrrole (DPP)-based small molecule presenting a terminal crosslinkable azido group, as a cathode modified layer for organic photovoltaics (OPVs) having the inverted device structure glass/indium tin oxide (ITO)/zinc oxide (ZnO) with or without interfacial layer (IFL)/active layer/MoO3/Ag. The active layer comprised a blend of poly[4,8-bis(5-(2-ethylhexyl)thien-2-yl)benzo[1,2-b;4,5-b´]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2-carboxylate-2,6-diyl] (PTB7-Th) as the electron donating moiety and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the electron acceptor. Atomic force microscopy, space charge-limited current mobility, surface energy, electron spectroscopy for chemical analysis depth profile, ultraviolet photoelectron spectroscopy analysis, and OPV performance data revealed that the surface status of ZnO changed after inserting the DPPBTDA/PCBM hybrid IFL and induced an optimized blend morphology, having a preferred gradient distribution of the conjugated polymer and PC71BM, for efficient carrier transport. The power conversion efficiency (AM 1.5 G, 1000 W m-2) of the device incorporating the hybrid IFL layer increased to 9.4 0.11% from 8.5 0.15% for the pre-optimized PTB7-Th/PCBM device (due primarily to an enhancement in the fill factor from 68.7 1.1 to 72.1 0.8%).