New X-shaped oligothiophenes for solution-processed solar cells

Abstract

Three new X-shaped conjugated oligothiophenes with 3 (1), 4 (2) and 6 (3) thiophenes on the arms were synthesized. 1 is oil, while 2 and 3 are solids. 1 and 2 have good solubility, while 3 has poor solubility. All compounds exhibit good thermal stability with decomposition temperatures over 340 °C. The absorption spectra of 1, 2, and 3 in thin films exhibit absorption maxima at 400, 426, and 466 nm, respectively. The HOMO and LUMO levels of 2 were estimated to be −5.29 eV and −3.16 eV, respectively. Solution-processed organic field-effect transistors based on 2 exhibit a hole mobility of 1.13 × 10⁻⁴ cm² V⁻¹s⁻¹ in air. Solution-processed organic solar cells based on blends of 2:PC₆₁BM or PC₇₁BM (1 : 2, w/w) exhibit power conversion efficiencies of 1.02 and 1.54%, respectively, under AM 1.5, 100 mW cm⁻².