Taking Me-4PACz as an example, the research team systematically revealed the mechanism of NiO in the NiO/Me-4PACz double hole transport layer. First, based on crystal structure analysis, it was found that compared with the ITO substrate, the NiO surface exposed fewer crystal plane types and higher metal atom density, indicating that NiO has a better structural basis for forming a uniform and dense Me-4PACz film. Secondly, through roughness and surface potential characterization, it was found that NiO nanocrystals can "planarize" the rough ITO substrate and form a more uniform Me-4PACz film. Then, combined with heating and vacuum-assisted experiments, it was verified that the binding force of hydroxyl groups on NiO is much stronger than that on the ITO substrate, which provides a stronger binding site for Me-4PACz. Based on the above three aspects, the wide-bandgap (~1.77 eV) perovskite solar cell prepared by the vacuum-assisted method achieved a photoelectric conversion efficiency of 19.55%. These findings not only deepen the understanding of SAMs assembly, but also provide important guidance for improving the stability and large-scale production of perovskite solar cells.
Figure 1. Crystalline properties of ITO and NiO films. (a) X-ray diffraction spectrum of ITO film. (b) Types of crystal planes exposed on the surface of ITO film. (c) Statistical graph of metal atom density on the crystal plane of ITO. (d) X-ray diffraction spectrum of NiO film. (e) Types of crystal planes exposed on the surface of NiO film. (f) Statistical graph of metal atom density on the crystal plane of NiO.
Figure 2. Surface morphology and Me-4PACz distribution of ITO and NiO films. (a−b) Surface morphology and cross-sectional profile of ITO. (c) KPFM images of ITO/Me-4PACz. (d−e) Surface morphology and cross-sectional profile of ITO/NiO. (f) KPFM images of ITO/NiO/Me-4PACz. (g) Cross-sectional growth model of ITO/Me-4PACz. (h) Cross-sectional growth model of ITO/NiO. (i) Cross-sectional growth model of ITO/NiO/Me-4PACz.
Figure 4. Performance of wide-bandgap perovskite devices. (a) Electron micrograph of device cross section. (b) Device efficiency statistics. (c) J-V curve of the champion device in forward and reverse scanning. (d) External quantum efficiency curve of the device. (e) Storage stability statistics of the device. (f) J-V curve and actual photo of a 1 cm2 device.
Acknowledgements
This work was supported by the National Natural Science Foundation of China, Optics Valley Laboratory Innovation Project, and Guangdong Key Laboratory of Digital Manufacturing Equipment. We would like to thank the Modern Analysis and Testing Center, Micro-Nano Manufacturing Process Platform, and Wuhan National Laboratory for Optoelectronics of Huazhong University of Science and Technology for their support in device preparation and characterization.
Afei Zhang, et. al., Role of NiO in wide-bandgap perovskite solar cells based on self-assembled monolayers, Chemical Engineering Journal, Volume 494, 2024, 153253, 1385-8947,
DOI:10.1016/j.cej.2024.153253.
https://www.sciencedirect.com/science/article/pii/S1385894724047417
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