Characterization of the Organic Thin Film Solar Cells with Active Layers of PTB7/PC71BM Prepared by Using Solvent Mixtures with Different Additives

Organic thin film solar cells (OTFSCs) were fabricated with blended active layers of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b: 4,5-b'.]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b]thiophenediyl]](PTB7)/[6,6]-phenyl-C-71-butyric (PC 71 BM). The performances of active layers are prepared in chlorobenzene (CB) with different additives of 1-chloronaphthalene (CN) and 1,8-Diiodooctane (DIO) by a wet process with spin coating technique. The effects of different solvent additives on photovoltaic parameters such as fill factor, short circuit current density, and power conversion efficiency of active layers are reported. The absorption and surface morphology of the active layers are investigated using UV-visible spectroscopy and atomic force microscopy, respectively. The results indicate that structural and morphological changes were induced by the additives with solvent. The current density-voltage (J-V) characteristics of photovoltaic cells were measured under the illumination of simulated solar light with 100 mW/cm(2) (AM 1.5 G) by an Oriel 1000 W solar simulator. The OTFSCs of PTB7/PC71 BM prepared with organic solvent additives of DIO+CN show more improved PCE of 4.96% by spin coating method.