Effect of additives on the photovoltaic properties of organic solar cells based on triphenylamine-containing amorphous molecules

Photovoltaic performance of the organic solar cells (OSCs) based on 2-((5′-(4-((4-((E)-2-(5′-(2,2-dicyanovinyl)-3′,4-dihexyl-2,2′-bithiophen-5-yl)vinyl) phenyl)(phenyl)amino)styryl)-4,4′-dihexyl-2,2′-bithiophen-5-yl)methylene)malononitrile (L(TPA-bTV-DCN)) as donor and PC₇₀BM as acceptor was optimized using 0.25 vol% high boiling point solvent additive of 1-chloronaphthalene (CN), 1,6-hexanedithiol (HDT), or 1,8-diodooctane (DIO). The optimized OSC based on L(TPA-bTV-DCN)-PC₇₀BM (1:2, w/w) with 0.25 vol% CN exhibits an enhanced power conversion efficiency (PCE) of 2.61%, with V _oc of 0.87 V, J _sc of 6.95 mA/cm², and FF of 43.2%, under the illumination of 100 mW/cm² AM 1.5 G simulated solar light, whereas the PCE of the OSC based on the same active layer without additive is only 1.79%. The effect of the additive on absorption spectra and the atomic force microscopy images of L(TPA-bTV-DCN)-PC70BM blend films were further investigated. The improved efficiency of the device could be ascribed to the enhanced absorption and optimized domain size in the L(TPA-bTV-DCN)-PC₇₀BM blend film.