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

Three organic donor-π-acceptor dyes 1-3 used for dye sensitized solar cells (DSSCs) with difference only in π spacer sequence were investigated via density functional theory (DFT) and time-dependent DFT calculations to shed light on how the π conjugation order influence the performance of the dyes. Key parameters in close connection with the open-circuit photovoltage (Voc) and the short-circuit current density (Jsc), including (i) light harvesting efficiency (LHE); (ii) injection driving force (ΔGinject.); (iii) reorganization energy (λreorg); (iv) number of photoinjected electrons (nc,inj); (v) the extent of charge recombination, and (vi) vertical dipole moment (μnormal), were discussed. The theoretical results reveal that compared with dyes 1 and 2, dye 3 has the largest Voc due to its largest μnormal 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.

Conjugation order effects on the performance of the D-π-A dyes used in DSSCs: A DFT and TDDFT analysisFigure optionsDownload as PowerPoint slideHighlights
► Conjugation order effects on DSSCs' efficiency were studied by DFT calculations.
► A set of key parameters affecting the efficiency of the cell have been discussed.
► Charge recombination is discussed through dye–I2 interaction.
► Dye 3 has the largest Voc due to the largest μnormal and slowest charge recombination.