Photophysical Properties and Photovoltaic Performance of Sensitizers with a Bipyrimidine Acceptor

Abstract

Molecular engineering is a crucial strategy for improving the photovoltaic performance of dye-sensitized solar cells (DSSCs). Despite the common use of the donor–π bridge–acceptor architecture in designing sensitizers, the underlying structure–performance relationship remains not fully understood. In this study, we synthesized and characterized three sensitizers: MOTP-Pyc, MOS₂P-Pyc, and MOTS₂P-Pyc, all featuring a bipyrimidine acceptor. Absorption spectra, cyclic voltammetry, and transient photoluminescence spectra reveal a photo-induced electron transfer (PET) process in the excited sensitizers. Electron spin resonance spectroscopy confirmed the presence of charge-separated states. The varying donor and π-bridge structures among the three sensitizers led to differences in their conjugation effect, influencing light absorption abilities and PET processes and ultimately impacting the photovoltaic performance. Among the synthesized sensitizers, MOTP-Pyc demonstrated a DSSC efficiency of 3.04%. Introducing an additional thienothiophene block into the π-bridge improved the DSSC efficiency to 4.47% for MOTS₂P-Pyc. Conversely, replacing the phenyl group with a thienothiophene block reduced DSSC efficiency to 2.14% for MOS₂P-Pyc. Given the proton-accepting ability of the bipyrimidine module, we treated the dye-sensitized TiO₂ photoanodes with hydroiodic acid (HI), significantly broadening the light absorption range. This treatment greatly enhanced the short-circuit current density of DSSCs owing to the enhanced electron-withdrawing ability of the acceptor. Consequently, the HI-treated MOTS₂P-Pyc-based DSSCs achieved the highest power conversion efficiency of 7.12%, comparable to that of the N719 dye at 7.09%. This work reveals the positive role of bipyrimidine in the design of organic sensitizers for DSSC applications.

References

[1] SavishaM, AbreezaM, AzimahO, et al. . Functionalized graphene quantum dots for dye-sensitized solar cell: key challenges, recent developments and future prospects. Renew Sustain Energy Rev, 2021, 144

[2] ZengK, TongZ, MaL, et al. . Molecular engineering strategies for fabricating efficient porphyrin-based dye-sensitized solar cells. Energy Environ Sci, 2020, 13(6): 1617-1657

[3] SharmaK, SharmaV, SharmaSS. Dye-sensitized solar cells: fundamentals and current status. Nanoscale Res Lett, 2018, 13(1): 381

[4] O’ReganB, GrätzelM. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO₂ films. Nature, 1991, 353: 737-740

[5] TomarN, AgrawalA, DhakaVS, et al. . Ruthenium complexes based dye sensitized solar cells: fundamentals and research trends. Sol Energy, 2020, 207: 59-76

[6] ZengK, ChenY, ZhuWH, et al. . Efficient solar cells based on concerted companion dyes containing two complementary components: an alternative approach for cosensitization. J Am Chem Soc, 2020, 142(11): 5154-5161

[7] DuvvaN, EomYK, ReddyG, et al. . Bulky phenanthroimidazole–phenothiazine D–π–A based organic sensitizers for application in efficient dye-sensitized solar cells. ACS Appl Energy Mater, 2020, 3(7): 6758-6767

[8] HengP, MaoL, GuoX, et al. . Accurate estimation of the photoelectric conversion efficiency of a series of anthracene-based organic dyes for dye-sensitized solar cells. J Mater Chem C, 2020, 8(7): 2388-2399

[9] KumarVS, MaryYS, PradhanK, et al. . Synthesis, spectral properties, chemical descriptors and light harvesting studies of a new bioactive azo imidazole compound. J Mol Struct, 2020, 1199

[10] Muñoz-GarcíaAB, BenesperiI, BoschlooG, et al. . Dye-sensitized solar cells strike back. Chem Soc Rev, 2021, 50(22): 12450-12550

[11] ChenCC, NguyenVS, ChiuHC, et al. . Anthracene-bridged sensitizers for dye-sensitized solar cells with 37% efficiency under dim light. Adv Energy Mater, 2022, 12(20): 2104051

[12] BradhaM, BalakrishnanN, SuvithaA, et al. . Experimental, computational analysis of Butein and Lanceoletin for natural dye-sensitized solar cells and stabilizing efficiency by IoT. Environ Dev Sustain, 2022, 24(6): 8807-8822

[13] TangY, WangY, LiX, et al. . Porphyrins containing a triphenylamine donor and up to eight alkoxy chains for dye-sensitized solar cells: a high efficiency of 10.9%. ACS Appl Mater Interfaces, 2015, 7(50): 27976-27985

[14] WuY, ZhuW. Organic sensitizers from D–π–A to D-A–π–A: effect of the internal electron-withdrawing units on molecular absorption, energy levels and photovoltaic performances. Chem Soc Rev, 2013, 42(5): 2039-2058

[15] DingWL, WangDM, GengZY, et al. . Molecular engineering of indoline-based D-A–π–A organic sensitizers toward high efficiency performance from first-principles calculations. J Phys Chem C, 2013, 117(34): 17382-17398

[16] YangJ, GanesanP, TeuscherJ, et al. . Influence of the donor size in D-π-A organic dyes for dye-sensitized solar cells. J Am Chem Soc, 2014, 136(15): 5722-5730

[17] LiuY, ZhangX, LiC, et al. . Energy-level control via molecular planarization and its effect on interfacial charge-transfer processes in dye-sensitized solar cells. J Phys Chem C, 2019, 123(22): 13531-13537

[18] Elmorsy MohamedR, Badawy SafaA, EhabAL, et al. . Significant improvement of dye-sensitized solar cell performance using low-band-gap chromophores based on triphenylamine and carbazole as strong donors. Dyes Pigm, 2023, 214

[19] DoK, KimD, ChoN, et al. . New type of organic sensitizers with a planar amine unit for efficient dye-sensitized solar cells. Org Lett, 2012, 14(1): 222-225

[20] RoyJK, KarS, LeszczynskiJ. Revealing the photophysical mechanism of N, N’-diphenyl-aniline based sensitizers with the D-D–π–A framework: theoretical insights. ACS Sustain Chem Eng, 2020, 8(35): 13328-13341

[21] WangZS, KoumuraN, CuiY, et al. . Hexylthiophene-functionalized carbazole dyes for efficient molecular photovoltaics: tuning of solar-cell performance by structural modification. Chem Mater, 2008, 20(12): 3993-4003

[22] JiaoY, MaoL, LiuS, et al. . Effects of meta or Para connected organic dyes for dye-sensitized solar cell. Dyes Pigm, 2018, 158: 165-174

[23] TianH, YangX, PanJ, et al. . A triphenylamine dye model for the study of intramolecular energy transfer and charge transfer in dye-sensitized solar cells. Adv Funct Materials, 2008, 18(21): 3461-3468

[24] ZhengZ, ShaoY, DingC, et al. . Rational design of ZL003-based organic dyes for highly efficient dye-sensitized solar cells: influence of alkynyl group and π–spacers on photovoltaic performance. J Mol Struct, 2022, 1269(5)

[25] ZhangJ, LiHB, SunSL, et al. . Density functional theory characterization and design of high-performance diarylamine-fluorenedyes with different π spacers for dye-sensitized solar cells. J Mater Chem, 2012, 22(2): 568-576

[26] YangF, AkhtaruzzamanM, IslamA, et al. . Structure–property relationship of naphthalene based donor–π–acceptor organic dyes for dye-sensitized solar cells: remarkable improvement of open-circuit photovoltage. J Mater Chem, 2012, 22(42): 22550-22557

[27] RenY, SunD, CaoY, et al. . A stable blue photosensitizer for color palette of dye-sensitized solar cells reaching 12.6% efficiency. J Am Chem Soc, 2018, 140(7): 2405-2408

[28] MarcoAB, Martínez de BarojaN, Andrés-CastánJM, et al. . Pyranylidene/thienothiophene-based organic sensitizers for dye-sensitized solar cells. Dyes Pigm, 2019, 161: 205-213

[29] ShahMF, MirloupA, ChowdhuryTH, et al. . A near-infrared thienyl-BODIPY co-sensitizer for high-efficiency dye-sensitized solar cells. Sustain Energy Fuels, 2019, 3(11): 2983-2989

[30] WanZ, JiaC, WangY, et al. . A strategy to boost the efficiency of rhodanine electron acceptor for organic dye: from nonconjugation to conjugation. ACS Appl Mater Interfaces, 2017, 9(30): 25225-25231

[31] TakeshitaT. DFT and TD-DFT study on azobenzene-based dye covalently attached to silane coupling agents: toward dye-sensitized TiO₂ catalyst and dye-sensitized solar cell applications. ChemistrySelect, 2021, 6(24): 6011-6018

[32] NagarajanB, ElumalaiR, et al. . Naphthalimide-phenothiazine based A’ –π–D–π–A featured organic dyes for dye sensitized solar cell applications. J Photochem Photobiol A Chem, 2021, 404: 112820

[33] HilalHM, El Bitar NehmeMA, GhaddarTH. Large enhancement of dye sensitized solar cell efficiency by co-sensitizing pyridyl- and carboxylic acid-based dyes. ACS Appl Energy Mater, 2018, 1(6): 2776-2783

[34] Al-QurashiOS, WazzanN. Prediction of power conversion efficiencies of diphenylthienylamine-based dyes adsorbed on the titanium dioxide nanotube. ACS Omega, 2021, 6(13): 8967-8975

[35] LinLY, TsaiCH, LinF, et al. . 2, 1, 3-Benzothiadiazole-containing donor–acceptor–acceptor dyes for dye-sensitized solar cells. Tetrahedron, 2012, 68(36): 7509-7516

[36] Ali ShahSA, SayyadMH, WahabF, et al. . Synthesis, modeling and photovoltaic properties of a benzothiadiazole based molecule for dye-sensitized solar cells. J Mater Sci Mater Electron, 2016, 27(5): 4501-4507

[37] LuF, YangG, XuQ, et al. . Tailoring the benzotriazole (BTZ) auxiliary acceptor in a D-A’ –π–A type sensitizer for high performance dye-sensitized solar cells (DSSCs). Dyes Pigm, 2018, 158: 195-203

[38] LinLY, TsaiCH, WongKT, et al. . Efficient organic DSSC sensitizers bearing an electron-deficient pyrimidine as an effective π-spacer. J Mater Chem, 2011, 21(16): 5950-5958

[39] SunH, LiPA, LiuD, et al. . Tuning photophysical properties via alkoxyl groups in charge-separated triphenylamine sensitizers for dye-sensitized solar cells. J Photochem Photobiol A Chem, 2019, 368: 233-241

[40] SunH, LiuD, WangT, et al. . Charge-separated sensitizers with enhanced intramolecular charge transfer for dye-sensitized solar cells: insight from structure-performance relationship. Org Electron, 2018, 61: 35-45

[41] GeF, XuF, GongK, et al. . Sensitizers designed toward efficient intramolecular charge separation for p-type dye-sensitized solar cells. Dyes Pigm, 2022, 200

[42] SunH, LiuD, WangT, et al. . Enhanced internal quantum efficiency in dye-sensitized solar cells: effect of long-lived charge-separated state of sensitizers. ACS Appl Mater Interfaces, 2017, 9(11): 9880-9891

[43] GuoM, HeR, DaiY, et al. . Electron-deficient pyrimidine adopted in porphyrin sensitizers: a theoretical interpretation of π-spacers leading to highly efficient photo-to-electric conversion performances in dye-sensitized solar cells. J Phys Chem C, 2012, 116(16): 9166-9179

[44] GuoM, LiM, DaiY, et al. . Exploring the role of varied-length spacers in charge transfer: a theoretical investigation on pyrimidine-bridged porphyrin dyes. RSC Adv, 2013, 3(38): 17515-17526

[45] FrischMJ, TrucksGW, SchlegelHB, et al. . Gaussian 16, revision A.03, 2016Wallingford, CTGaussian Inc

[46] BeckeAD. Density-functional thermochemistry. III. The role of exact exchange. J Chem Phys, 1993, 98(7): 5648-5652

[47] LeeC, YangW, ParrRG. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys Rev B Condens Matter, 1988, 37(2): 785-789

[48] YuHS, HeX, LiSL, et al. . MN15:a Kohn-Sham global-hybrid exchange-correlation density functional with broad accuracy for multi-reference and single-reference systems and noncovalent interactions. Chem Sci, 2016, 7(8): 5032-5051

[49] BaroneV, CossiM, TomasiJ. A new definition of cavities for the computation of solvation free energies by the polarizable continuum model. J Chem Phys, 1997, 107(8): 3210-3221

[50] LiY, RenT, DongWJ. Tuning photophysical properties of triphenylamine and aromatic cyano conjugate-based wavelength-shifting compounds by manipulating intramolecular charge transfer strength. J Photochem Photobiol A Chem, 2013, 251: 1-9

[51] HadsadeeS, PromarakV, SudyoadsukT, et al. . Theoretical study on factors influencing the efficiency of D–π’–A’–π–A isoindigo-based sensitizer for dye-sensitized solar cells. J Electron Mater, 2020, 49(1): 318-332

[52] ChoiIT, JuMJ, KangSH, et al. . Structural effect of carbazole-based coadsorbents on the photovoltaic performance of organic dye-sensitized solar cells. J Mater Chem A, 2013, 1(32): 9114-9121

[53] TingareYS, ShenMT, SuC, et al. . Novel oxindole based sensitizers: synthesis and application in dye-sensitized solar cells. Org Lett, 2013, 15(17): 4292-4295

[54] XuF, GongK, FanW, et al. . J-aggregated dyes for dye-sensitized solar cells: suppressing aggregation-induced excited-state quenching by intramolecular charge separation. ACS Appl Energy Mater, 2022, 5(11): 13780-13790

[55] KumariR, MiltonMD. Design and synthesis of multi-stimuli responsive π-extended phenothiazine aldehydes: solvatochromism, acidochromism, moisture detection and fluorochromic sensing of amine vapors. Dyes Pigm, 2022, 205

[56] MaimaitiyimingX, AbodurexitiA, DongmulatiN. Syntheses, characterization and properties of Poly(2, 5:didodecyloxy-1, 4-diethynyl-phenylene-alt-2-N, N-dimethyl amino-4, 6-pyrimidine). Mater Chem Phys, 2020, 240

[57] SeçkinAB. Effect of electron donor groups on the performance of benzothiadiazole dyes with simple structures for dye-sensitized solar cells. J Photochem Photobiol A Chem, 2024, 449

[58] HanBY, PanTY, WuYC, et al. . Steric effect of N-substituted triphenylamine on double-anchored phenothiazine dye-sensitized solar cells. ACS Appl Energy Mater, 2023, 6(7): 3778-3788

[59] WangJ, LiM, QiD, et al. . Exploring photophysical properties of metal-free coumarin sensitizers: an efficient strategy to improve the performance of dye-sensitized solar cells. RSC Adv, 2014, 4(96): 53927-53938

[60] HsiehJB, YenSC, HammoudF, et al. . Effect of terminal alkyl chains for free radical photopolymerization based on triphenylamine oxime ester visible-light absorbing type I photoinitiators. ChemistrySelect, 2023, 8(30)

[61] KarakirovaY, MladenovaR. An EPR study of gamma irradiated mixed materials based on sucrose for dosimetric purposes. Radiat Phys Chem, 2022, 197

[62] MaoL, ZhouM, ShiX, et al. . Triphenylamine (TPA) radical cations and related macrocycles. Chin Chem Lett, 2021, 32(11): 3331-3341

[63] FengW, GengR, LiuD, et al. . A charge-separated interfacial hole transport semiconductor for efficient and stable perovskite solar cells. Org Electron, 2021, 88

[64] FeldtSM, LohsePW, KesslerF, et al. . Regeneration and recombination kinetics in cobalt polypyridine based dye-sensitized solar cells, explained using Marcus theory. Phys Chem Chem Phys, 2013, 15(19): 7087-7097

[65] Dang QuangLN, KaliamurthyAK, HaoNH. Co-sensitization of metal based N719 and metal free D35 dyes: an effective strategy to improve the performance of DSSC. Opt Mater, 2021, 111

[66] Su’aitMS, RahmanMYA, AhmadA. Review on polymer electrolyte in dye-sensitized solar cells (DSSCs). Sol Energy, 2015, 115: 452-470

[67] RobsonKCD, HuK, MeyerGJ, et al. . Atomic level resolution of dye regeneration in the dye-sensitized solar cell. J Am Chem Soc, 2013, 135(5): 1961-1971

[68] ChenK, ZengY, GaoX, et al. . Organic semiconductor based on N, S-containing crown ether enabling efficient and stable perovskite solar cells. Chemsuschem, 2024, 17(4)

[69] PlanellsM, PellejàL, CliffordJN, et al. . Energy levels, charge injection, charge recombination and dye regeneration dynamics for donor–acceptor π-conjugated organic dyes in mesoscopic TiO₂ sensitized solar cells. Energy Environ Sci, 2011, 4(5): 1820-1829

[70] LiSB, GuDM, ZhangJ, et al. . Theoretical design and characterization of high-efficiency organic dyes with different electron-withdrawing groups based on C275 toward dye-sensitized solar cells. New J Chem, 2016, 40(11): 9320-9328