Electron‐Acceptor‐Dependent Light Absorption, Excited‐State Relaxation, and Charge Generation in Triphenylamine Dye‐Sensitized Solar Cells

Abstract

By choosing a simple triphenylamine electron donor, we herein compare the influence of electron acceptors benzothiadiazole benzoic acid (BTBA) and cyanoacrylic acid (CA), on energy levels, light absorption, and dynamics of excited-state evolution and electron injection. DFT and time-dependent DFT calculations disclosed remarkable intramolecular conformational changes for the excited states of these two donor-acceptor dyes. Photoinduced dihedral angle variation occurs to the triphenylamine unit in the CA dye and backbone planarization happens to conjugated aromatic blocks in the BTBA dye. Femtosecond spectroscopic measurements suggested the crucial role of having a long excited-state lifetime in maintaining a high electron-injection yield because a reduced driving force for a low energy-gap dye can result in slower electron-injection dynamics.

Finding the Way to Solar Fuels with Dye-Sensitized Photoelectrosynthesis Cells

“…Electron injection into TiO 2 , extensively studied, ,− ,,,− is kinetically complex, a characteristic commonly attributed to hetero­geneities in the oxide. ,,, Electron injection can occur by direct light-driven electron transfer from a donor level on the chromophore to an acceptor level in the semiconductor ,, or, more commonly, from an excited state or states following light absorption. ,,,,,,,,− ,− From the experimental data for −RuP 2+ and its analogues on TiO 2 , the initial electron injection process or processes occur on the hundreds of femtoseconds to hundreds of picoseconds time scale from the initially formed singlet MLCT state(s), TiO 2 |− 1 {[(4,4′-(PO 3 H 2 ) 2 ­bpy – )­Ru III ­(bpy) 2 ] 2+ *}, before 1 MLCT → 3 MLCT internal conversion can occur. Electron injection can also take place from non-thermally equilibrated 3 MLCT states before they undergo vibrational relaxation.…”

Energy‐Loss Reduction as a Strategy to Improve the Efficiency of Dye‐Sensitized Solar Cells

“…Thus far, highly efficient silicon or PSCs usually show an E Loss as low as 0.4–0.5 eV, and the recent boost in PCEs of OSCs based on non‐fullerene acceptors can be also attributed to the continuous reduction in E Loss . However, a much larger E Loss can be observed in DSSCs, which usually originates from the undesired loss of energy in the driving force for electron injection after photoexcitation and dye regeneration, combined with interfacial charge recombination loss reactions (Figure ) . Therefore, it is strategically important to reduce energy losses as much as possible by optimization of efficient charge transfer reactions, improving DSSC performance.…”

Thienochrysenocarbazole‐Based Dyes for Solar Cell: A Theoretical Investigation of the Tethering‐Position‐Related Influence of Triple‐Bond on the Electronic and Optical Properties

“…However, many newly developed D/A infrared dyes with small energy‐gaps based on CA acceptor have critical kinetic limitations such as low electron injection efficiency, which is probably induced by the short singlet excited‐state lifetimes of organic dyes . It has been demonstrated that the replacement of CA with more electron‐deficient unit benzothiadiazole‐benzoic acid (BTBA), can bring forth energy‐gap shrinkage concomitant with prolonged lifetime of excited‐state, which are highly desirable for more efficient DSCs.…”