Increasing the Open-Circuit Voltage in High-Performance Organic Photovoltaic Devices through Conformational Twisting of an Indacenodithiophene-Based Conjugated Polymer

A fused ladder indacenodithiophene (IDT)-based donor-acceptor (D-A)-type alternating conjugated polymer, PIDTHT-BT, presenting n-hexylthiophene conjugated side chains is prepared. By extending the degree of intramolecular repulsion through the conjugated side chain moieties, an energy level for the highest occupied molecular orbital (HOMO) of -5.46 eV - a value approximately 0.27 eV lower than that of its counterpart PIDTDT-BT - is obtained, subsequently providing a fabricated solar cell with a high open-circuit voltage of approximately 0.947 V. The hole mobility (determined using the space charge-limited current model) in a blend film containing 20 wt% PIDTHT-BT) and 80 wt% [6,6]-phenyl-C-71 butyric acid methyl ester (PC71BM) is 2.2 x 10(-9) m(2) V-1 s(-1), which is within the range of reasonable values for applications in organic photovoltaics. The power conversion efficiency is 4.5% under simulated solar illumination (AM 1.5G, 100 mW cm(-2)).