Increasing the open-circuit voltage in high-performance organic photovoltaic devices through conformational twisting of an indacenodithiophene- based conjugated polymer

摘要

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 (PC_(71)BM) is 2.2 × 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)). An indacenodithiophene-based conjugated polymer presenting pendant n-hexylthiophene as conjugated side chains is synthesized. A deep HOMO energy level of -5.46 eV is obtained due to conformational twisting of the polymer main chain, induced by the side chain conjugated units. An open circuit voltage of 0.947 V and PCE up to 4.5% can be achieved.