Theoretical Study On P-type Triphenylamine-based Sensitizers

The n-type dye sensitizers are well developed at present.Therefore,the development of p-type sensitizers is key to enhance the photoelectric conversion efficiency of dyes-sensitized solar cells（DSSCs）.Non-metallic triphenylamine dyes have been found to have better photoelectric conversion efficiency.In this paper,density functional theory（DFT）combined with time-dependent DFT（TD-DFT）is used to study the light absorption performance and electronic performance of triphenylamine dyes,also forecasts the dye light harvesting efficiency（LHE）,hole injection(ΔG_inj),dye regeneration(ΔG_reg)and charge restructuring(ΔG_CR).The highest occupied orbital（HOMO）and lowest unoccupied orbital（LUMO）energy levels of the modified dye are located below of Ni O semiconductor energy level and above the I₃^?/I^?redox potential,respectively,which meet the requirements of ideal dyes.The specific research results are as follows:1.A series of triphenylamine-based dyes WS1-WS7 were designed with W1 as the prototype to investigate the effects of the attached electron donor D on the absorption spectra and electronic properties of the dyes.The calculated data show that insertion of D not only results in a red-shift in the absorption spectra for all dyes but also achieves a broader absorption for visible light.Compared with that of the prototype,the absorption peak of the dye WS7 has a red-shift of 95 nm and an oscillator strength increase of 29%.The absorption peak of WS7 is wider and stronger,and the absorption range extends to 900 nm.The LHE andΔG_reg values of WS7 are 0.991 and-1.49 e V,respectively.On overall evaluation,WS7 is a promising candidate of a p-type dye sensitizer with good light absorption and dye regeneration efficiency.2.Six p-type dyes with D-π-A structures were designed.The results showed that the enhanced conjugation ofπ-linkers increases the coplanarity and decreases HOMO-LUMO gap of the dyes.The absorption spectra of dyes 1-6 are obviously red-shifted.Compared with design prototype QT-1,the spectra of dyes 3 and 6 are red-shifted by 128 and 154 nm,and the oscillator strengths are improved by 70%and 71%,respectively.The absorption peaks of dyes 3 and 6 are strongest,and the absorption area in the range of 400-900 nm are large,indicating the absorption performance are stronger.They also have the maximum charge separation degree（t）,which is beneficial to reduce the return of holes.Furthermore,LHE,ΔG_inj,ΔG_reg andΔG_CR of dyes 3 and 6 are superior to those of other dyes.In addition,the bromine substitution can effectively promote the red-shift of the absorption spectra.3.The effect of anchor group on dye properties was studied by changing the strong electron-absorbing carboxyl group to the weak electron-absorbing pyridine group and the electron-supplying catechol group to transform the double-chain dye P1 with better performance.In addition,the conjugation of enhanced conjugate groups to improve and optimize the properties of dye molecules.The results show that pyridine and catechol groups can promote the red-shift absorption of dye.Combine with two thiophene and benzothiadiazole of dye P4,DF4 and DZ4 whether in the absorption spectrum,or in LHE,ΔG_inj,ΔG_reg andΔG_CR performance has more superior performance,is excepted to become the sensitizing agent with excellent performance.