How to design proper π-spacer order of the D-π-A dyes for DSSCs? A density functional response

Three organic donor-pi-acceptor dyes 1-3 used for dye sensitized solar cells (DSSCs) with difference only in pi spacer sequence were investigated via density functional theory (OFT) and time-dependent OFT calculations to shed light on how the pi conjugation order influence the performance of the dyes. Key parameters in close connection with the open-circuit photovoltage (V-oc) and the short-circuit current density (J(sc)), including (i) light harvesting efficiency (LHE); (ii) injection driving force (Delta G(inject)): (iii) reorganization energy (lambda(reorg)); (iv) number of photoinjected electrons (n(c,inj)); (v) the extent of charge recombination, and (vi) vertical dipole moment (mu(normal)), were discussed. The theoretical results reveal that compared with dyes 1 and 2, dye 3 has the largest V-oc due to its largest mu(normal) and the slowest charge recombination. This conclusion is in good accordance with the experimental results and the theoretical criteria we used would be useful to design and fast screen other organic dyes. (C) 2012 Elsevier Ltd. All rights reserved.