Theoretical Study On Triphenylamine-based P-type Dyes For DSSCs

The structural and electronic properties of prototype and designed dyes were investigated by computational techniques.Structure optimization,electronic level and absorption characters are calculated with density functional theory(DFT)and time-dependent DFT(TDDFT)at the CAM-B3LYP/6-31(d,p).The solvent effect was involved using PCM model in chloroform.The modified dyes meet the basic requirements of both-?Ginj and-?Greg being over 0.2 eV for an efficient hole injection and dye regeneration,respectively.All the designed p-type dyes have smaller energy gap and significant red shift in absorption spectra than that of the reference dyes.1.By replacing the 2-methylidenepropanedinitrile acceptor with 1,3-diethyl-5-methylene-2-thioxo-dihydropyrimidine-4,6(1H,5H)-dione,the electronic and optical characters of 4,4'-(4-(5-(2,2-dicyanovinyl)thiophen-2-yl)phenylazanediyl)dibenzoic acid(02)and its hypothetical dyes 03-07 were calculated.Designed p-type dyes 03-07 have smaller energy gap and significant red shift in absorption spectra than that of the reference 02.Finally,our results suggested that 03-07 have larger light-harvesting efficiencies(LHE)in the visible spectral regions of 400 um to 700 um than O2.Among all the dyes,05 is expected to have excellent performance as a p-type sensitized dye in solar cells due to its great LHE and sufficient hole injection efficiency.2.Based on prototype W2,we designed triarylamine-based p-type sensitizers W2-1 to W2-7 that contain an additional acceptors(A'),a ?-spacer and two anchors.For W2-1 to W2-4,instead of 2,1,3-Benzothiadiazole in W2,thieno[3,4-b]-1,4-dioxin,thiophene,"2?482-Thieno[3,4-c][1,2,5]thiadizole,thiazolo[5,4-d]thiazole are A' acceptor and thiophene as ?-spacer.For W2-5 to W2-8,A' and ? are same,with 2,1,3-benzothiadiazole,thieno[3,4-b]-1,4-dioxin,"2?482-Thieno[3,4-c][1,2,5]thiadiazo,thiazolo[5,4-d]thiazole respectively as the additional acceptors.The highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)guarantee the sufficient hole injection and dye regeneration.W2-4 has higher light-harvesting efficiency(LHE)(0.994)and larger overlap with the visible light from 400 nm to 600 nm.Finally,the results suggest that the driving force of hole injection,dye regeneration and charge recombination(?Ginj,?Greg and ?GCR)of W2-4 is the best one with more negative?Ginj(-4.33),?Greg(-1.74)and more positive ?GCR(1.92).It is a effective way to replace 2,1,3-Benzothiadiazole with thiazolo[5,4-d]thiazole as A' acceptor to improve the performance of the dyes.And using thiazolo[5,4-d]thiazole group can improve the absorption ability and hinder charge recombination.3.The triphenylamine-based sensitizers O2-A-O2-Ewere designed as the p-type dyes in the form of D-?-A chain.1-ethyl-4-methyl-2,5-dihydro-lH-1,2,3-triazole,1,3,4-oxadiazole,benzo[c][1,2,5]thiadiazole,4-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole,4-(1,3,4-oxadiazol-2-yl)benzo[c][1,2,5]thiadiazole were designed as ?-linker.Some important characters such as absorption spectra,electronic transition,electronic structres of sensitizers were systematically studied.It was found that the absorption bands of O2-C and O2-D red-shift and have broad band in the visible light area at 524 nm and 559nm,respectively.Both ?Ginj and?Greg of their values are negative which is good for hole injection and dye regeneration.Positive ?GCR values could reduce charge recombination which is benefit for charge transferring from the donor to the acceptor.Importantly,dye O2-C and O2-Dmay be promising candidates for the p-type sensitizers in comparison with prototype O2.