Chlorine-Substituent Regulation in Dopant-Free Small-Molecule Hole-Transport Materials Improves the Efficiency and Stability of Inverted Perovskite Solar Cells

Abstract

Although doped hole-transport materials (HTMs) offer an efficiency benefit for perovskite solar cells (PSCs), they inevitably diminish the stability. Here, we describe the use of various chlorinated small molecules, specifically fluorenone-triphenylamine (FO-TPA)-x-Cl [x = para, meta, and ortho (p, m, and o)], with different chlorine-substituent positions, as dopant-free HTMs for PSCs. These chlorinated molecules feature a symmetrical donor–acceptor–donor structure and ideal intramolecular charge transfer properties, allowing for self-doping and the establishment of built-in potentials for improving charge extraction. Highly efficient hole-transfer interfaces are constructed between perovskites and these HTMs by strategically modifying the chlorine substitution. Thus, the chlorinated HTM-derived inverted PSCs exhibited superior efficiencies and air stabilities. Importantly, the dopant-free HTM FO-TPA-o-Cl not only attains a power conversion efficiency of 20.82% but also demonstrates exceptional stability, retaining 93.8% of its initial efficiency even after a 30-day aging test conducted under ambient air conditions in PSCs without encapsulation. These findings underscore the critical role of chlorine-substituent regulation in HTMs in ensuring the formation and maintenance of efficient and stable PSCs.

Keywords

Hole-transport materials / Inverted perovskite solar cells / Chlorinated small molecules / Donor–acceptor–donor structure

References

[1.] Min H, Lee DY, Kim J, et al.. Perovskite solar cells with atomically coherent interlayers on SnO₂ electrodes. Nature, 2021, 598(7881): 444-450,

[2.] Kojima A, Teshima K, Shirai Y, et al.. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. J Am Chem Soc, 2009, 131(17): 6050-6051,

[3.] Yang WS, Park BW, Jung EH, et al.. Iodide management in formamidinium-lead-halide-based perovskite layers for efficient solar cells. Science, 2017, 356(6345): 1376-1379,

[4.] Lin X, Cui D, Luo X, et al.. Efficiency progress of inverted perovskite solar cells. Energy Environ Sci, 2020, 13(11): 3823-3847,

[5.] Li W, Martínez-Ferrero E, Palomares E. Self-assembled molecules as selective contacts for efficient and stable perovskite solar cells. Mater Chem Front, 2024, 8(3): 681-699,

[6.] Kim D, Jung HJ, Park IJ, et al.. Efficient, stable silicon tandem cells enabled by anion-engineered wide-bandgap perovskites. Science, 2020, 368(6487): 155-160,

[7.] Yang D, Sano T, Yaguchi Y, et al.. Achieving 20% efficiency for low-temperature-processed inverted perovskite solar cells. Adv Funct Mater, 2019, 29(12): 1807556,

[8.] Ameen S, Rub MA, Kosa SA, et al.. Perovskite solar cells: influence of hole transporting materials on power conversion efficiency. Chemsuschem, 2016, 9(1): 10-27,

[9.] Bakr ZH, Wali Q, Fakharuddin A, et al.. Advances in hole transport materials engineering for stable and efficient perovskite solar cells. Nano Energy, 2017, 34: 271-305,

[10.] Yuan J, Chen Y, Liu X, et al.. Dopant-free hole-transporting materials for CH₃NH₃PbI₃ inverted perovskite solar cells with an approximate efficiency of 20%. ACS Appl Energy Mater, 2021, 4(6): 5756-5766,

[11.] Guo S, Zhang X, Li Z, et al.. Dopant-free ternary conjugated polymeric hole-transporting materials for efficient inverted planar perovskite solar cells. Sol RRL, 2021, 5(10): 2100506,

[12.] Zhang H, Wang H, Zhu H, et al.. Low-temperature solution-processed CuCrO₂ hole-transporting layer for efficient and photostable perovskite solar cells. Adv Energy Mater, 2018, 8(13): 1702762,

[13.] Jeng JY, Chiang YF, Lee MH, et al.. CH₃NH₃PbI₃ perovskite/fullerene planar-heterojunction hybrid solar cells. Adv Mater, 2013, 25(27): 3727-3732,

[14.] Shao Y, Yuan Y, Huang J. Correlation of energy disorder and open-circuit voltage in hybrid perovskite solar cells. Nat Energy, 2016, 1: 15001,

[15.] Hawash Z, Ono LK, Qi Y. Moisture and oxygen enhance conductivity of LiTFSI-doped spiro-MeOTAD hole transport layer in perovskite solar cells. Adv Mater Interfaces, 2021, 8(23): 1600117,

[16.] Hawash Z, Ono LK, Raga SR, et al.. Air-exposure induced dopant redistribution and energy level shifts in spin-coated spiro-MeOTAD films. Chem Mater, 2015, 27(2): 562-569,

[17.] Niu G, Guo X, Wang L. Review of recent progress in chemical stability of perovskite solar cells. J Mater Chem A, 2015, 3(17): 8970-8980,

[18.] Yu X, Li Z, Sun X, et al.. Dopant-free dicyanofluoranthene-based hole transporting material with low cost enables efficient flexible perovskite solar cells. Nano Energy, 2021, 82: 105701,

[19.] Wang YK, Ma H, Chen Q, et al.. Fluorinating dopant-free small-molecule hole-transport material to enhance the photovoltaic property. ACS Appl Mater Interfaces, 2021, 13(6): 7705-7713,

[20.] Li R, Li C, Liu M, et al.. Hydrogen-bonded dopant-free hole transport material enables efficient and stable inverted perovskite solar cells. CCS Chem, 2022, 4(9): 3084-3094,

[21.] Huang J, Yang J, Sun H, et al.. A cost-effective D-A-D type hole-transport material enabling 20% efficiency inverted perovskite solar cells. Chin J Chem, 2021, 39(6): 1545-1552,

[22.] Chen W, Wang Y, Liu B, et al.. Engineering of dendritic dopant-free hole transport molecules: enabling ultrahigh fill factor in perovskite solar cells with optimized dendron construction. Sci China Chem, 2021, 64(1): 41-51,

[23.] Yang K, Liao Q, Huang J, et al.. Intramolecular noncovalent interaction-enabled dopant-free hole-transporting materials for high-performance inverted perovskite solar cells. Angew Chem Int Edit, 2022, 61(2): e202113749,

[24.] Cai N, Li F, Chen Y, et al.. Synergistical dipole-dipole interaction induced self-assembly of phenoxazine-based hole-transporting materials for efficient and stable inverted perovskite solar cells. Angew Chem Int Edit, 2021, 60(37): 20437-20442,

[25.] Wu J, Hu M, Zhang L, et al.. Fluorinated cross-linkable and dopant-free hole transporting materials for efficient and stable perovskite solar cells. Chem Eng J, 2021, 422: 130124,

[26.] Zhou Z, Wu Q, Cheng R, et al.. Orientation-engineered small-molecule semiconductors as dopant-free hole transporting materials for efficient and stable perovskite solar cells. Adv Funct Mater, 2021, 31(20): 2011270,

[27.] Sun Q, Zhang J, Chen Q, et al.. High-efficiency planar p–i–n perovskite solar cells based on dopant-free dibenzo[b, d]furan-centred linear hole transporting material. J Power Sources, 2020, 449: 227488,

[28.] Zhang J, Sun Q, Chen Q, et al.. Dibenzo[b, d]thiophene-cored hole-transport material with passivation effect enabling the high-efficiency planar p–i–n perovskite solar cells with 83% fill factor. Sol RRL, 2020, 4(3): 1900421,

[29.] Wang Y, Chen Q, Fu J, et al.. Annealing- and doping-free hole transport material for p–i–n perovskite solar cells with efficiency achieving over 21%. Chem Eng J, 2022, 433: 133265,

[30.] Tian Y, Tao L, Chen C, et al.. Facile synthesized fluorine substituted benzothiadiazole based dopant-free hole transport material for high efficiency perovskite solar cell. Dyes Pigments, 2021, 184: 108786,

[31.] Tao L, Chen C, Wu C, et al.. Fluorine-substituted benzotriazole core building block-based highly efficient hole-transporting materials for mesoporous perovskite solar cells. Sol RRL, 2020, 4(3): 1900362,

[32.] Sun Y, Peng Y, Zhao C, et al.. The strategy for high-efficiency hole conductors by engineering short-range intramolecular interactions. Dyes Pigments, 2022, 197: 109889,

[33.] Bai QQ, Huang J, Guo H, et al.. Regioisomeric polymer semiconductors based on cyano-functionalized dialkoxybithiophenes: structure–property relationship and photovoltaic performance. Trans Tianjin Univ, 2022, 28(5): 385-397,

[34.] Ren J, Qu J, Chen J, et al.. Fluorinated dopant-free hole-transporting material for efficient and stable perovskite solar cells with carbon cathode. J Power Sources, 2018, 401: 29-36,

[35.] Li B, Li SY, Yang X, et al.. Understanding the impact of fluorine substitution on the photovoltaic performance of block copolymers. Trans Tianjin Univ, 2022, 28(5): 406-413,

[36.] Zhang Z, Shen L, Wang S, et al.. Halogenated hole-transport molecules with enhanced isotropic coordination capability enable improved interface and light stability of perovskite solar cells. Adv Energy Mater, 2023, 13(14): 2204362,

[37.] Zhao W, Li S, Yao H, et al.. Molecular optimization enables over 13% efficiency in organic solar cells. J Am Chem Soc, 2017, 139(21): 7148-7151,

[38.] Luo Z, Liu T, Wang Y, et al.. Reduced energy loss enabled by a chlorinated thiophene-fused ending-group small molecular acceptor for efficient nonfullerene organic solar cells with 13.6% efficiency. Adv Energy Mater, 2019, 9(18): 1900041,

[39.] Ma F, Zhao Y, Qu Z, et al.. Developments of highly efficient perovskite solar cells. Acc Mater Res, 2023, 4(8): 716-725,

[40.] Park J, Kim J, Yun HS, et al.. Controlled growth of perovskite layers with volatile alkylammonium chlorides. Nature, 2023, 616(7958): 724-730,

[41.] Zhang H, Wu Y, Zhang W, et al.. Low cost and stable quinoxaline-based hole-transporting materials with a D-A-D molecular configuration for efficient perovskite solar cells. Chem Sci, 2018, 9(27): 5919-5928,

[42.] Xu P, Liu P, Li Y, et al.. D-A-D-typed hole transport materials for efficient perovskite solar cells: tuning photovoltaic properties via the acceptor group. ACS Appl Mater Interfaces, 2018, 10(23): 19697-19703,

[43.] Zhang H, Yao H, Hou J, et al.. Over 14% efficiency in organic solar cells enabled by chlorinated nonfullerene small-molecule acceptors. Adv Mater, 2018, 30(28): e1800613,

[44.] Zhang S, Qin Y, Zhu J, et al.. Over 14% efficiency in polymer solar cells enabled by a chlorinated polymer donor. Adv Mater, 2018, 30(20): e1800868,

[45.] Yoon WS, Kim DW, Choi MW, et al.. Designing 1, 5-naphthyridine-2, 6-dione-based conjugated polymers for higher crystallinity and enhanced light absorption to achieve 9.63% efficiency polymer solar cells. Adv Energy Mater, 2018, 8(2): 1701467,

[46.] Finley JP. Using the local density approximation and the LYP, BLYP and B3LYP functionals within reference-state one-particle density-matrix theory. Mol Phys, 2004, 102(7): 627-639,

[47.] Lu T, Chen F. Multiwfn: a multifunctional wavefunction analyzer. J Comput Chem, 2012, 33(5): 580-592,

[48.] Fu Q, Liu H, Gao Y, et al.. Tunable molecular packing of dopant-free hole-transport polymers for perovskite solar cells. ACS Energy Lett, 2023, 8(7): 2878-2885,

[49.] Wang K, Liu J, Yin J, et al.. Defect passivation in perovskite solar cells by cyano-based π-conjugated molecules for improved performance and stability. Adv Funct Mater, 2020, 30(35): 2002861,

[50.] Gao Y, Wu Y, Liu Y, et al.. Interface and grain boundary passivation for efficient and stable perovskite solar cells: the effect of terminal groups in hydrophobic fused benzothiadiazole-based organic semiconductors. Nanoscale Horiz, 2020, 5(12): 1574-1585,

[51.] Li H, Wu G, Li W, et al.. Additive engineering to grow micron-sized grains for stable high efficiency perovskite solar cells. Adv Sci, 2019, 6(18): 1901241,

[52.] Bi C, Wang Q, Shao Y, et al.. Non-wetting surface-driven high-aspect-ratio crystalline grain growth for efficient hybrid perovskite solar cells. Nat Commun, 2015, 6: 7747,

[53.] Tong T, Tan C, Keller T, et al.. Two anthracene-based copolymers as the hole-transporting materials for high-performance inverted (p–i–n) perovskite solar cells. Macromolecules, 2018, 51(18): 7407-7416,

[54.] Zhang T, Guo N, Li G, et al.. A controllable fabrication of grain boundary PbI₂ nanoplates passivated lead halide perovskites for high performance solar cells. Nano Energy, 2016, 26: 50-56,

[55.] Stolterfoht M, Wolff CM, Márquez JA, et al.. Visualization and suppression of interfacial recombination for high-efficiency large-area pin perovskite solar cells. Nat Energy, 2018, 3: 847-854,

[56.] Belisle RA, Jain P, Prasanna R, et al.. Minimal effect of the hole-transport material ionization potential on the open-circuit voltage of perovskite solar cells. ACS Energy Lett, 2016, 1(3): 556-560,

[57.] Afraj SN, Zheng D, Velusamy A, et al.. 2, 3-diphenylthieno[3, 4-b]pyrazines as hole-transporting materials for stable, high-performance perovskite solar cells. ACS Energy Lett, 2022, 7(6): 2118-2127,

[58.] Liu P, Wang W, Liu S, et al.. Fundamental understanding of photocurrent hysteresis in perovskite solar cells. Adv Energy Mater, 2019, 9(13): 1803017,