Screening novel XY1b-based organic dyes by modifying electron-assisted acceptors for dye-sensitised solar cells: a theoretical analysis

To screen efficient organic dyes, six novel XY1b-based molecules are designed by modifying electron-assisted acceptors, and their electronic structure, optical properties and photovoltaic performances are evaluated in detail with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations coupled with the incoherent charge transfer model. Results show that benzoselenadiazole (BSD) and diketopyrrolopyrrole (DPP) are two best electron-assisted acceptors and replacing benzothiadiazole (BTD) with the BSD/DPP unit can redshift the maximum absorption peak by 13/67 nm. According to our estimation, the overall photoelectric conversion efficiency (PCE) of XY1b is as high as 13.09% with a J(sc) of 16.261 mAcm(-2), V-oc of 1.047 V and FF of 0.769, in good agreement with its measured value of 11.8 +/- 0.2% (J(sc )= 15.26 +/- 0.18 mAcm(-2), V-oc = 1.01 +/- 0.003 V and FF = 76.3 +/- 0.2%), verifying that the scheme proposed by us is reliable. With the same procedure, the predicted PCE values for dyes 1, 2 and 5 reach up to 18.00%, 15.95% and 27.37% respectively, indicating that these three dyes are potential efficient sensitisers and are worthy of further study by experiments.