Simple donor-acceptor molecule with long exciton diffusion length for organic photovoltaics

To succeed in commercial applications, donor materials for organic solar cells should combine high stability and simple synthesis with high performance in devices. Here, we present a new small pi-conjugated molecule, TPA-T-DCV-Ph, which meets those requirements. Simple and efficient three-step synthesis produces a push-pull molecule with triphenylamine donor and phenyldicyanovinyl acceptor groups, which is suitable for both solution processing and vacuum deposition. The unique property of TPA-T-DCV-Ph is an unusually long exciton diffusion length of > 25 nm due to the combined effect of long exciton lifetime and surprisingly low energy disorder. This, together with a device engineering, resulted in > 5% efficiency for TPA-T-DCV-Ph:C-70 vacuum-processed solar cells. The results obtained are envisioned to be further improved by optimizing the absorption of the molecule and light management in the device which can push the efficiency even further.