Enhanced crystal formation of methylammonium lead iodide via self-assembled monolayers and their solvation for perovskite solar cells
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The quality of a perovskite photo-absorber layer is strongly dependent on the morphology of initially deposited PbI2 precursor film. In this work, surface modification of titanium dioxide (TiO2) substrates with self-assembled monolayers (SAMs) was performed to control the quality of the PbI2 and MAPbI3 perovskite layers. Two small organic molecules, each with a different backbone, 3-aminopropanoic acid (APA) and 4-aminobenzoic acid (ABA), were selected and their solvation effects were also investigated. Small homogeneously distributed cracks were found in the PbI2 film produced from the modification with APA molecules in demethyl sulfoxide or ethanol solution, whereas films produced from modification with ABA molecules showed different effects. These small cavities act as pathway for MAI intercalation and facilate PbI2-to-MAPbI3 conversion, leading to PbI2-free perovskite film. The different morphologies were caused by different adsorption behaviors of each SAM on the TiO2 surface. APA molecules interact with the hydroxyl groups of TiO2 while ABA molecules do not. Therefore, with APA treatment, the perovskite solar cells showed improvements in power conversion efficiency in comparison to either the devices without surface modification or ones treated with ABA molecules. The reasons behind the enhancement are attributed to longer charge carrier lifetime and better charge transfer at the TiO2/APA/perovskite interface. The results imply that the choice selected for SAMs and their solvents are crucial to obtaining high quality perovskite layers and efficient perovskite solar cells.
Fourier transform infrared spectroscopy
Field emission scanning electron microscopy
Short-circuit current density
Power conversion efficiency
The authors would like to thank Dr. Chawalit Bhoomanee and Mr. Anusit Kaewprajak for assistance in the device preparation and measurement. Also, we would like to thank Dr. Atipong Ngamjarurojana for assistance in photoluminescence measurement. The authors would like to extend our gratitude to Cynthia Bail for her assistance with English language editing end proofreading.
PR developed the idea of the research, assisted fabrication and characterization of perovskite solar cells, analyzed data, and finalized the manuscript. KC mainly conducted the experiments, analyzed data and drafted the manuscript. DW, SC, and TS analyzed data and helped in developing the idea. All authors read and approved the final manuscript.
This research was financially supported by the Thailand Research Fund (TRF) (Grant No. MRG6080006). This work was also partially supported by Chiang Mai University, Thailand.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no competing interest.
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