Near-infrared absorption bacteriochlorophyll derivatives as biomaterial electron donor for organic solar cells

In this paper, we investigate two bacteriochlorophyll (BChl) derivatives, namely methyl (pyro) bacteriopheophorbide a [BChl-(2)1], with excellent absorption in near-infrared regions as donor materials for organic solar cells (OSCs). In the meantime, we prepare two methyl (pyro)pheophorbide a [Chl-(2)1] as reference to make a comparison. Compared to the small red-shifts of absorption bands of Chls-1/2 after forming the thin film through spin coating of the homogeneous solution, the absorption spectra of BChls-1/2 exhibited larger red-shifts from the absorption peak at 750 nm in the solution to the absorption peak at 860 nm after forming the solid film. This significant absorption shift is attributed to the formation of J-type aggregates by intermolecular pi-pi stacking among the BChl-1/2 molecules. What's more the absorbed sunlight of the BChls-1/2 aggregates at the near-infrared (NIR) region can be transferred into photocurrent which can be proved from the EQE indicating the energy and electron transferring between BChl aggregates are efficient. The optimized power conversion efficiency (PCE) value of 1.43% under standard AM1.5 mW/cm(2) sunlight was achieved with the BCh1-1: C-70 planarheterojunction (PH]) cells. 2017 Elsevier B.V. All rights reserved.