Single and double branched organic dyes based on carbazole and red-absorbing cationic indolium for p-type dye-sensitized solar cells: A combined experimental and theoretical investigation. (February 2018)

• Record Type: Journal Article
• Authors: Bao, Le Quoc; Ho, Phuong; Chitumalla, Ramesh Kumar; Jang, Joonkyung; Thogiti, Suresh; Kim, Jae Hong
• Is Part Of: Dyes and pigments. Volume 149(2018)
• Page Start: 25
• Page End: 36
• Publication Date: 2018-02
• Subjects: p-type dye-sensitized solar cells -- Carbazole -- Cationic dye -- Charge transfer -- Photocurrent density; Dyes and dyeing -- Periodicals; Pigments -- Periodicals; 667.2
• DOI: 10.1016/j.dyepig.2017.09.042
• Languages: English
• ISSNs: 0143-7208

Abstract

Abstract: A series of novel single and double branched carbazole-based red-absorbing cationic dyes without (CSI and CDI) and with (CST and CDT) a thiophene spacer have been synthesized for p-type dye-sensitized solar cells ( p -DSSCs). The introduction of the red-absorbing cationic acceptor/thiophene spacer led to the broadening and bathochromic shift of the absorption maxima from an onset of 600 nm for CSI to 800 nm for CDT as well as improved molar absorptivity. The introduction of the double branching/thiophene spacer lowered the lowest unoccupied molecular orbital (LUMO) levels of CDI, CST, and CDT, making their potentials more positive than that of CSI. Among these, the double branched CDI exhibited the highest conversion efficiency of 0.112%. Furthermore, all of the dyes examined outperformed the standard C343 dye (0.062%), measured under similar fabrication conditions. Despite the decreased photovoltaic performance as a result of the introduction of the thiophene spacer, overall, the double branched dyes exhibited better interfacial charge transfer that led to higher JSC and VOC values compared to those of singly branched dyes. Electrochemical impedance spectroscopy analysis showed that double branched dyes have much lower charge transfer resistance and increased hole lifetime than single branched dyes. Density functional theory (DFT) and time-dependent DFT calculations were performed to theoretically characterize the optical and electrochemical properties of the synthesized dyes. Graphical abstract: Doule branched dyes showed better interfacial charge transfer and hole lifetime over single branched dyes leading to enhanced photovoltaic performance. Highlights: Red absorbing indolium-based single and di-branched (DB) dyes were synthesized. The result shows that DB dyes exhibited higher efficiency than single branched dyes. EIS calculations indicate that DB dyes exhibit good charge transfer properties. Also showed increased hole-lifetime than single branched dyes.