Photophysical and photovoltaic properties of truxene-functionalized conjugated polymer–fullerene supramolecular complexes

Abstract

We report the synthesis, characterization, and photophysical and photovoltaic properties of two truxene-functionalized conjugated copolymers (P1 and P2) containing various 2,1,3-benzothiadiazole segments; P1 and P2 were synthesized using Suzuki and Heck coupling reactions, respectively. The number-average molecular weights of P1 and P2 were 1.76 × 10⁴ and 4.58 × 10³ g mol⁻¹, respectively, and the corresponding polydispersity indices were 1.47 and 2.16, respectively. Photoluminescence titrations and density functional theory calculations demonstrated that the supramolecular complexes between these polymers and a fullerene derivative, [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM), exhibited moderate first step-wise association constants of K_a1 (3.4 × 10⁴ M⁻¹ for P1 and 1.0 × 10⁴ M⁻¹ for P2). Furthermore, ultraviolet-visible-near-infrared spectroscopy and spectroelectrochemical measurements showed that P1 cations were induced in the P1–PC₆₁BM complex, indicating efficient electron transfer from P1 to PC₆₁BM. A P1/PC₆₁BM device with an equivalent weight of 1 : 1 exhibited a power conversion efficiency (PCE) of up to 0.53%, which was higher than that of a device composed of a P2/PC₆₁BM blend (0.47%). The PCE improvement was attributed to stronger non-covalent interactions between P1 and PC₆₁BM, suggesting that P1 is a promising material for polymeric solar cell applications.