Two T-Shaped Donor–Acceptor Small Molecules Based on 4,9-Di(thiophen-2-yl)naphtho[2,3-b]thiophene for Solution-Processed Organic Solar Cells

Two novel T-shaped π-conjugated small molecules of DTNT-3DPP and DTNT(DPP-PN) 3 with 4,9-di(thiophen-2-yl)naphtho[2,3- b ]thiophene (DTNT) as the donor core and diketopyrrolopyrrole (DPP) as acceptor arms, in the latter case incorporating phenanthrene (PN) units, have been designed and synthesized. The effects of the central core and terminal units on the optical, thermal, electrochemical, and photovoltaic properties have been investigated. It was found that DTNT-3DPP and DTNT(DPP-PN) 3 exhibit better light-harvesting and charge-transport properties than triphenylamine (TPA)-based star-shaped molecules. DTNT-3DPP and DTNT(DPP-PN) 3 were used as donor materials and methyl [6,6]-phenyl-C 71 -butyrate (PC 71 BM) as the acceptor for the fabrication of solution-processed bulk heterojunction (BHJ) solar cells. The power conversion efficiencies (PCEs) of solar cells based on DTNT-3DPP and DTNT(DPP-PN) 3 are 3.47 and 3.69 %, respectively. These PCEs are higher than those of the corresponding TPA-based solar cells (1.91 and 3.67 %). Our work indicates that the planar DTNT unit can improve the photovoltaic properties of organic small molecules relative to those of the TPA unit. Graphical Two novel T-shaped π-conjugated small molecules (SMs) based on 4,9-di(thiophen-2-yl)naphtho[2,3- b ]thiophene as the donor core and diketopyrrolopyrrole as acceptor arms have been synthesized. The SMs exhibit better light-harvesting and charge-transport properties than triphenylamine-based molecules. The power conversion efficiencies of solar cells based on the two SMs are 3.47 and 3.69 %.