Synthesis of all-conjugated poly(3-hexylthiophene)-block- poly(3-(4′-(3″,7″-dimethyloctyloxy)-3′-pyridinyl)thiophene) and its blend for photovoltaic applications

New all-conjugated block copolythiophene, poly(3-hexylthiophene)-block-poly(3-(4′-(3″,7″-dimethyloctyloxy)-3′-pyridinyl)thiophene) (P3HT-b-P3PyT) was successfully prepared by Grignard metathesis polymerization. The supramolecular interaction between [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) and P3PyT was proposed to control the aggregated size of PCBM and long-term thermal stability of the photovoltaic cell, as evidenced by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and optical microscopy. The effect of different solvents on the electronic and optoelectronic properties was studied, including chloroform (CL), dichlorobenzene (DCB), and mixed solvent of CL/DCB. The optimized bulk heterojunction solar cell devices using the P3HT-b-P3PyT/PCBM blend showed a power conversion efficiency of 2.12%, comparable to that of P3HT/PCBM device despite the fact that former had a lower crystallinity or absorption coefficient. Furthermore, P3HT-b-P3PyT could be also used as a surfactant to enhance the long-term thermal stability of P3HT/PCBM-based solar cells by limiting the aggregated size of PCBM. This study represents a new supramolecular approach to design all-conjugated block copolymers for high-performance photovoltaic devices.