Starburst Triphenylamine-Based Donor–Acceptor-Type Small Molecules for Solution-Processed Organic Solar Cells

A class of the donor–acceptor (D–A)-type organic small molecules that includes TPA-DPP, DTPA-DPP, and TTPA-DPP [TPA = triphenylamine, DPP = diketopyrrolopyrrole, DTPA = bis(triphenylamine), TTPA = tris(triphenylamine)] was synthesized; these compounds contain TPA as a donor unit and DPP as an acceptor unit. Solution-processed organic solar cells (OSCs) with these compounds as donors and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an acceptor were fabricated. The starburst OSCs prepared from DTPA-DPP and TTPA-DPP with two and three TPA units, respectively, exhibited better photovoltaic performance than the OSC prepared with one TPA unit, because DTPA-DPP and TTPA-DPP have better light-harvesting properties and charge-transport properties. The DTPA-DPP-based OSCs delivered a power conversion efficiency (PCE) of 2.26 % and the TTPA-DPP-based OSCs exhibited a higher PCE of 2.47 %. The PCE level is 1.15 and 1.25 times higher than that in the TPA-DPP-based OSCs, respectively. Our work indicates that a starburst configuration can improve the photovoltaic properties of D–A-type organic small molecules in OSCs.