Oligothiophene-bridged bis(arylene ethynylene) small molecules for solution-processible organic solar cells with high open-circuit voltage

A new series of conjugated oligothiophene-bridged bis(arylene ethynylene) small molecules have been designed, synthesized, and characterized by photophysical, electrochemical and computational methods. These compounds were found to have optimal LUMO levels that ensure effective charge transfer from these compounds to [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₀BM). They were utilized as good electron-donor materials that can be blended with electron-acceptor PC₇₀BM in the fabrication of solution-processed molecular bulk heterojunction (BHJ) solar cells. All of these BHJ devices showed very high open-circuit voltage (V_oc) of 0.90-0.97 V, and the best power conversion efficiency achieved was 3.68 %. The high V_oc is consistent with the deeper low-lying HOMO level and is relatively insensitive to the donor: acceptor blend ratio. The spin-coated thin films of these small molecules showed p-channel field-effect charge transport with the hole mobilities of up to 2.04×10^-4 cm² V^-1 s^-1. These compounds illuminate the potential of solution-processible small-molecular aryl acetylide compounds for efficient power generation in photovoltaic implementation. Building bridges: New oligothiophene-bridged bis(arylene ethynylene) small molecules (see picture) are developed and applied in solution-processed organic solar cells. All of these photovoltaic devices showed very high open-circuit voltage of over 0.90 V, and the best power conversion efficiency achieved was 3.68 %.