Y-shaped metal-free D-pi-(A)(2) sensitizers for high-performance dye-sensitized solar cells

A series of 2,3,5-substituted thiophene-based metal-free dyes with two anchoring groups, D-pi-(A)(2) (DA), were synthesized for application in DSSCs. Different arylamines and 2-cyanoacrylic acid were used as the electron donor and the electron acceptor, respectively. The DSSC based on DA5 has the best power conversion efficiency (7.28%) among all devices, which is 2 times higher than that of S1 with only one anchoring group. With addition of a co-adsorbent, CDCA, the device performance of all the DA-based DSSCs are improved by 1.03 to 2-fold, with the best efficiency (7.87%) reaching 95% of that of the N719-based standard cell (8.28%). Compared with the S1 congener with only one anchor, the DA dyes can more effectively suppress charge recombination and increase electron injection efficiency, leading to higher open-circuit voltage and short-circuit current.