Rational molecular engineering of cyclopentadithiophene-bridged D-A-π-A sensitizers combining high photovoltaic efficiency with rapid dye adsorption

Abstract

Dye-sensitized solar cell (DSSC) is considered as a feasible route to the clean and renewable energy conversion technique. The commercial application requires further enhancements on photovoltaic efficiency and simplification on the device fabrication. For avoiding the unpreferable trade-off between photocurrent (JSC) and photovoltage (VOC), here we report the molecular engineering and comprehensive photovoltaic characterization of three cyclopentadithiophene-bridged D-A-π-A motif sensitizers with a change in donor group. We make a careful choice on the donor and conjugation bridge for synergistically increasing JSC and VOC. Comparing with the reference dye WS-2, the photovoltaic efficiency with the single component dye of WS-51 increases by 18%, among one of the rare examples in pure metal-free organic dyes exceeding 10% in combination with traditional iodine redox couples. Moreover, WS-51 exhibits several prominent merits on potentially scale-up industrial application: i) facile synthetic route to target molecule, ii) simple dipping procedure without requirement of co-sensitization, and iii) rapid dye adsorption capability.

Effect of an auxiliary acceptor on D–A–π–A sensitizers for highly efficient and stable dye-sensitized solar cells

“…All of the three compounds exhibit three major electronic absorption bands: i) the electron transitions in UV region (around 300-350 nm), ii) the ICT band in visible region (around 560 nm for B-87 and Q-85, 590 nm for Q-93), iii) the additional absorption band or shoulder from subordinate orbital transition (near 500 nm). Compared with the reported WS-51 (λmax = 551 nm), 13 the absorption maximum of B-87 (λmax = 562 nm) is 11 nm redshifted along with a slight enhancement of molar extinction coefficient (ε) from 43000 to 47400 M -1 cm -1 . Interestingly, the two PP-based dyes, Q-85 and B-87 have similar band shapes with B-87 showing an identical λmax and an enhancement of ε to 50600 M -1 cm -1 for the latter compoud.…”

“…As expected, the dye deprotonation and aggregation on TiO2 film result in a shift and broadening of the absorption spectra that the maximum absorption peaks for B-87, Q-85 and Q-93 are blue-shifted to 543 nm, 543 nm and 586 nm, respectively. 13 Please do not adjust margins Please do not adjust margins…”

“…1 H NMR (400 MHz, CDCl3) δ 8.68 (s, 1H), 7.67 (dd, J = 10.8, 8.8 Hz, 4H), 6.89 (dd, J = 8.8, 2.4 Hz, 4H), 4.00 (t, J = 6.5 Hz, 4H), 1.88 -1.74 (m, 4H), 1.52 -1.40 (m, 4H), 1.39 -1.15 (m, 32H), 0.88 (t, J = 6.8 Hz, 6H). 13 C NMR (101 MHz, CDCl3) δ 161. 29, 160.96, 157.66, 155.57, 146.66, 145.80, 142.14, 135.61, 131.94, 131.68, 129.67, 129.49, 119.96, 114.53, 68.21, 68.19, 31.93, 29.68, 29.65, 29.62, 29.59, 29.41, 29.37, 29.19, 29.17, 26.03, 22.71, 14.14 10,13-dibromo-3,6-didodecyldibenzo[f,h]pyrido [3,4b]quinoxaline (3c): A solution of 1 (0.80 mg, 3.0 mmol) and 2c (1.09 g, 2.0 mmol) in 30.0 mL ethanol was added acetic acid (10.0 ml).…”

“…As noted above, the design of DSSCs molecular dyes requires careful consideration of multiple opto-electronic properties, such as band alignment and optical absorption coefficient, as well as solid-state properties such as dye aggregation, morphology, and mode of assembly on the TiO2 photoanode. Zhu and co-workers performed extensive studies on 2,1,3benzothiadiazole (BTD)-based sensitizers with this D−A−π−A motif, and the PCE of the DSSCs has been improved from 8.7% (WS-2) 6 to 9.0% (WS-9), 10 then to 10.08% (WS-51) 13 by changing different π-bridges to decrease the intermolecular interactions and retard the charge recombination. Inspired by their previous work, we substituted the cyclopenta[2,1-b:3,4-b']dithiophene (CPDT) with 4-bis (2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene (DTS) which is found to work very effectively on reducing dye aggregation as well as preventing charge recombination due to the presence of two out of plane 2-ethylhexyl.…”

Molecular Engineering of Pyrido[3,4‐b]pyrazine‐Based Donor–Acceptor–π‐Acceptor Organic Sensitizers: Effect of Auxiliary Acceptor in Cobalt‐ and Iodine‐Based Electrolytes

“…[3][4][5][6][7][8][9][10][11][12] Recently,a ni mproved D-p-A construction,t he so-called D-A-p-A, in which an auxiliary heteroannulateda cceptor [13] is introducedi nto the molecular framework, has been systematically developed, which has led to excellent photovoltaic performance and photostability. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] To date, several D-A-p-Abased organics ensitizers have exhibited high powerc onversion efficiencies (PCEs) of over 10 %u nder full sun illumination (AM 1.5G, 100 mW cm À2 ), such as the indoline sensitizer YA422 (10.65 %), [31] the porphyrin sensitizer GY50 (12.75 %), [32] and the record one SM315 (13.0 %). [33] Compared to classical ruthenium sensitizers, such pure organic sensitizers are very promising candidates for future commerciala nd practical application, showingc omparably high PCEs and long-term stability.…”