Investigation of Surface Morphology and Nano-Mechanical Behavior of PTB7-Th:PCBM Thin Films
Keywords:
Annealing, organic photovoltaics, nano-indentations, surface morphologyAbstract
Purpose: This study investigates the morphological stability and nanomechanical properties of PTB7-Th:PCBM thin films on two substrates under thermal stress, focusing on the effects of thermal annealing on morphology and mechanical response.
Design/methodology/approach: PTB7-Th:PCBM thin films were deposited on glass substrates and subjected to thermal annealing at 150 °C. The morphological changes and nanomechanical properties of the films were investigated, including surface roughness, indentation depth, drift rate, and unload-ing behavior. The effect of changing the substrate from glass to glass/ITO on the nanomechanical response was also examined.
Findings: Thermal annealing at 150 °C resulted in a maximum reduction in surface roughness of 2.151 nm and promoted robust nanocrystalline ordering of PCBM. The nanomechanical response exhibited a distinct pop-out phenomenon during unloading, together with uniform film characteris-tics and excellent reproducibility. The pop-out phenomenon disappeared when the substrate was changed from glass to glass/ITO, indicating that its occurrence is influenced by both temperature and the substrate–film interface. An average indentation depth of 756.4 nm was obtained at an average drift rate of 0.346 nm/s.
Originality: This study highlights the substrate-dependent pop-out behavior of PTB7-Th:PCBM films, providing new insight into their nanomechanical response and stability.
Research limitations/implications: Further studies are needed to optimize annealing and substrate conditions for improved film stability.
Practical implications: Thermal treatment and substrate interfaces are crucial for stable and efficient organic photovoltaics.
Social implications: Improved film stability may support the development of durable, flexible, and low-cost solar-energy technologies.
References
Chen, C.-P., Tsai, Y.-Y., Chen, Y.-C. and Li, Y.-H. (2018), "High-performance and long-term stable inverted ternary solar cells based on PTB7-Th/N2200/PC71BM blends", Solar Energy, Vol. 176, pp. 170-177.
Cui, Y., Yao, H., Gao, B., Qin, Y., Zhang, S., Yang, B., He, C., Xu, B. and Hou, J. (2017), "Fine-tuned photoactive and interconnection layers for achieving over 13% efficiency in a fullerene-free tandem organic solar cell", Journal of the American Chemical Society, Vol. 139 No. 21, pp. 7302-7309.
Ding, P., Yang, D., Yang, S. and Ge, Z. (2024), "Stability of organic solar cells: toward commercial applications", Chemical Society Reviews, Vol. 53 No. 5, pp. 2350-2387.
Göken, M. and Kempf, M. (2001), "Pop-ins in Nanoindentations – the Initial Yield Point", Vol. 92 No. 9, pp. 1061-1067.
He, Z., Xiao, B., Liu, F., Wu, H., Yang, Y., Xiao, S., Wang, C., Russell, T. P. and Cao, Y. (2015), "Single-junction polymer solar cells with high efficiency and photovoltage", Nature Photonics, Vol. 9 No. 3, pp. 174-179.
Karagiannidis, P., Kassavetis, S., Pitsalidis, C. and Logothetidis, S. (2011), "Thermal annealing effect on the nanomechanical properties and structure of P3HT: PCBM thin films", Thin Solid Films, Vol. 519 No. 12, pp. 4105-4109.
Kwon, O. K., Uddin, M. A., Park, J.-H., Park, S. K., Nguyen, T. L., Woo, H. Y. and Park, S. Y. (2015), "A High Efficiency Nonfullerene Organic Solar Cell with Optimized Crystalline Organizations", Advanced Materials (Deerfield Beach, Fla.), Vol. 28 No. 5, pp. 910-916.
Li-Juan, D., Su-Ling, Z., Zheng, X., Ling, Z. and Lin, W. (2016), "Mechanism of ternary polymer solar cells based on P3HT: PTB7-Th: PCBM", ACTA PHYSICA SINICA, Vol. 65 No. 7.
Li, N. and Brabec, C. J. (2015), "Air-processed polymer tandem solar cells with power conversion efficiency exceeding 10%", Energy & Environmental Science, Vol. 8 No. 10, pp. 2902-2909.
Liang, A., Li, C., Zou, B., Chung, S., Kim, B., Cho, Y., Zhong, J., Zhao, J., Tan, L. and Zhang, G. (2026), "20.46% efficient organic solar cells with concurrent voltage enhancement and thermal stability enabled by crystallization-kinetics-controlled morphology", Energy & Environmental Science, Vol. 19 No. 11, pp. 3487-3499.
Liao, S.-H., Jhuo, H.-J., Cheng, Y.-S. and Chen, S.-A. (2013), "Fullerene derivative-doped zinc oxide nanofilm as the cathode of inverted polymer solar cells with low-bandgap polymer (PTB7-Th) for high performance", Advanced Materials (Deerfield Beach, Fla.), Vol. 25 No. 34, pp. 4766-4771.
Liao, S.-H., Jhuo, H.-J., Yeh, P.-N., Cheng, Y.-S., Li, Y.-L., Lee, Y.-H., Sharma, S. and Chen, S.-A. (2014), "Single junction inverted polymer solar cell reaching power conversion efficiency 10.31% by employing dual-doped zinc oxide nano-film as cathode interlayer", Scientific reports, Vol. 4 No. 1, pp. 6813.
Liu, Q., Toudert, J., Liu, F., Mantilla‐Perez, P., Bajo, M. M., Russell, T. P. and Martorell, J. (2017), "Circumventing UV Light Induced Nanomorphology Disorder to Achieve Long Lifetime PTB7‐Th: PCBM Based Solar Cells", Advanced Energy Materials, Vol. 7 No. 21, pp. 1701201.
Luong, H. M., Chae, S., Yi, A., Ding, K., Huang, J., Kim, B. M., Welton, C., Chen, J., Wakidi, H. and Du, Z. (2023), "Impact of thermal stress on device physics and morphology in organic photodetectors", ACS Energy Letters, Vol. 8 No. 5, pp. 2130-2140.
Ma, J., Chang, J., Lin, Z., Guo, X., Zhou, L., Liu, Z., Xi, H., Chen, D., Zhang, C. and Hao, Y. (2018), "Elucidating the roles of TiCl4 and PCBM fullerene treatment on TiO2 electron transporting layer for highly efficient planar perovskite solar cells", The Journal of Physical Chemistry C, Vol. 122 No. 2, pp. 1044-1053.
Ma, Z., Dong, Y., Su, Y.-J., Yu, R., Gao, H., Gong, Y., Lee, Z.-Y., Yang, C., Hsu, C.-S. and Tan, Z. a. (2022), "Morphological stabilization in organic solar cells via a fluorene-based crosslinker for enhanced efficiency and thermal stability", ACS applied materials & interfaces, Vol. 14 No. 1, pp. 1187-1194.
Mikroyannidis, J. A., Kabanakis, A. N., Sharma, S. and Sharma, G. D. (2011), "A simple and effective modification of PCBM for use as an electron acceptor in efficient bulk heterojunction solar cells", Advanced Functional Materials, Vol. 21 No. 4, pp. 746-755.
Morvillo, P., Bobeico, E., Esposito, S. and Diana, R. (2012), "Effect of the active layer thickness on the device performance of polymer solar cells having [60] PCBM and [70] PCBM as electron acceptor", Energy Procedia, Vol. 31, pp. 69-73.
Nam, S., Seo, J., Woo, S., Kim, W. H., Kim, H., Bradley, D. D. and Kim, Y. (2015), "Inverted polymer fullerene solar cells exceeding 10% efficiency with poly (2-ethyl-2-oxazoline) nanodots on electron-collecting buffer layers", Nature communications, Vol. 6 No. 1, pp. 8929.
Ohmura, T. and Wakeda, M. (2021), "Pop-in phenomenon as a fundamental plasticity probed by nanoindentation technique", Materials, Vol. 14 No. 8, pp. 1879.
Qi, Q., Xian, K., Ke, H., Wu, J., Zhou, K., Gao, M., Liu, J., Li, S., Zhao, W. and Chen, Z. (2022), "Improving the thermal stability of organic solar cells via crystallinity control", ACS Applied Energy Materials, Vol. 5 No. 12, pp. 15656-15665.
Qin, J., Xi, Q., Wu, N., Liu, B., Yue, C., Fang, J., Wang, Z., Du, Y., Zhang, Q. and Wang, Z. (2025), "Improved damp heat and thermal cycling stability of organic solar cells", Nature Energy, Vol. 10 No. 12, pp. 1439-1449.
Shah, S. A. A., Sayyad, M. H., Abdulkarim, S. and Qiao, Q. (2018), "Step-by-step heating of dye solution for efficient solar energy harvesting in dye-sensitized solar cells", Journal of Electronic Materials, Vol. 47 No. 8, pp. 4737-4741.
Shah, S. A. A., Sayyad, M. H., Nasr, N., Toor, R. A., Sajjad, S., Elbohy, H. and Qiao, Q. (2017), "Photovoltaic performance and impedance spectroscopy of a purely organic dye and most common metallic dye based dye-sensitized solar cells", Journal of Materials Science: Materials in Electronics, Vol. 28 No. 9, pp. 6552-6559.
Shah, S. A. A., Sayyad, M. H., Wahab, F., Khan, K. A., Munawar, M. A., Elbohy, H. and Qiao, Q. (2016), "Synthesis, modeling and photovoltaic properties of a benzothiadiazole based molecule for dye-sensitized solar cells", Journal of Materials Science: Materials in Electronics, Vol. 27 No. 5, pp. 4501-4507.
Shu, K., Zhang, C., Hou, P., Zheng, D., Gu, L. and Wang, L. (2020), "Crack evolution in diamond-like carbon films on steel substrates during nano-indentation", Diamond and Related Materials, Vol. 106, pp. 107829.
Song, L., Wang, W., Barabino, E., Yang, D., Körstgens, V., Zhang, P., Roth, S. V. and Müller-Buschbaum, P. (2019), "Composition–morphology correlation in PTB7-Th/PC71BM blend films for organic solar cells", ACS applied materials & interfaces, Vol. 11 No. 3, pp. 3125-3135.
Vogelbaum, H. S. and Sauvé, G. (2017), "Recently developed high-efficiency organic photoactive materials for printable photovoltaic cells: a mini review", Synthetic metals, Vol. 223, pp. 107-121.
Wan, J., Xu, X., Zhang, G., Li, Y., Feng, K. and Peng, Q. (2017), "Highly efficient halogen-free solvent processed small-molecule organic solar cells enabled by material design and device engineering", Energy & Environmental Science, Vol. 10 No. 8, pp. 1739-1745.
Xia, Y., Xu, X., Aguirre, L. E. and Inganäs, O. (2018), "Semitransparent all-polymer solar cells through lamination", Journal of Materials Chemistry A, Vol. 6 No. 42, pp. 21186-21192.
Xiao, B., Zhao, Y., Tang, A., Wang, H., Yang, J. and Zhou, E. (2017), "PTB7-Th based organic solar cell with a high Voc of 1.05 V by modulating the LUMO energy level of benzotriazole-containing non-fullerene acceptor", Science bulletin, Vol. 62 No. 18, pp. 1275-1282.
Zhou, F., Xu, L., Deng, C., Song, J., Deng, C., Wang, Y. and Liu, M. (2020), "Nanomechanical characterization of nanostructured La2 (Zr0. 75Ce0. 25) 2O7 thermal barrier coatings by nanoindentation", Applied Surface Science, Vol. 505, pp. 144585.
Zhou, L., Chang, J., Liu, Z., Sun, X., Lin, Z., Chen, D., Zhang, C., Zhang, J. and Hao, Y. (2018), "Enhanced planar perovskite solar cell efficiency and stability using a perovskite/PCBM heterojunction formed in one step", Nanoscale, Vol. 10 No. 6, pp. 3053-3059.
Downloads
Published
Issue
Section
Categories
License
Copyright (c) 2026 Muhammad Riaz, Iqra Munir, Nida, Noor Ul Huda, Rabia Shahzad (Author)
This work is licensed under a Creative Commons Attribution 4.0 International License.
