Amphiphilic conjugated block copolymers for efficient bulk heterojunction solar cells

Abstract

The synthesis of random and diblock copolymers of poly(3-alkylthiophene)s bearing polar substituents was successfully developed by GRIM polymerization. 3-Hexyl-thiophene was successfully copolymerised with a new derivative, 3-functionalised-thiophene (propyl 5-(2-(thiophen-3-yl)ethoxy)pentanoate), bearing an ester function. Under optimized conditions, this ester proved to be fully compatible with the Grignard metathesis polymerization. Saponification of the copolymer esters provided the corresponding polyacids. Photovoltaic properties of copolymers were investigated in bulk heterojunction devices with PC₆₁BM as acceptor. Among all the amphiphilic copolymers, P3HT-bb-P3AcidHT showed the best performance with a PCE of 4.2%, an open-circuit voltage (V_oc) of 0.60 V, a short-circuit current density (J_sc) of 13.0 mA cm⁻², and a fill factor (FF) of 0.60.