Functionalized Thienopyrazines on NiOx Film as Self-Assembled Monolayer for Efficient Tin-Perovskite Solar Cells Using a Two-Step Method
We collaborated with the group of Ming-Chou Chen at National Central University to develop a series of organic molecules, thienopyrazine (TP), for which TP-MN (1), TP-CA (2), and TPT-MN (3) were designed and synthesized as self-assembled monolayers (SAMs) deposited on the NiOx film for tin-perovskite solar cells (TPSCs). The structure of the TP-MN (1) single crystal was successfully grown and analyzed to support the uniform SAM produced on the ITO/NiOx substrate. When we used NiOx as HTM in TPSC, the device showed poor performance. To improve the efficiency of TPSC, we utilized a combination of new organic SAMs with NiOx HTM, the TPSC device exhibited the highest PCE of 7.7% for TP-MN (1). Hence, the designed NiOx/TP-MN (1) acts as a new model system for the development of efficient SAM-based TPSC. To the best of our knowledge, the combination of organic SAMs with anchoring CN/CN or CN/COOH groups, and NiOx HTM for TPSC has never been reported elsewhere. This method of combining organic SAMs with NiOx HTM thus provides a good modification methodology for the future development of SAM-based TPSC. The TPSC device based on the NiOx/TP-MN bilayer exhibits great enduring stability for performance, retaining ~80% of its original value for shelf storage over 4000 h.
C.-H. Kuan, S.N. Afraj, Y.-L. Huang, A.Velusamy, C.-L. Liu, T.-Y. Su, X. Jiang, J.-M. Lin, M.-C. Chen* and Eric W.-G. Diau *, “Functionalized Thienopyrazines on NiOx Film as Self-Assembled Monolayer for Efficient Tin-Perovskite Solar Cells Using a Two-Step Method”, Angew. Chem. Int. Ed., 63, e202407228 (2024).
Quadruple-Cation Wide-Bandgap Mixed-Halide Tin Perovskite Solar Cells
Tin-based perovskite solar cell (TPSC) is a promising alternative to the traditional lead-based PSC for lead-free photovoltaic applications. To further promote the performance and stability, a tandem type of TPSC is an attracting direction to pursue. To serve as a low-bandgap TPSC with the bandgap (Eg) of around 1.4 eV, searching for a high-bandgap TPSC with Eg in the range 1.8-2.0 eV is an important task to build a lead-free tandem TPSC. Herein, we introduce a quadruple-cation perovskite system to solve the problem of phase segregation for the Br2I tin perovskite that contains 55% FA+, 25% MA+, 10% Cs+, and 10% PMA+ (FA0.55MA0.25Cs0.1PMA0.1SnBr2I, abbreviated as PMA) with a favoring Eg of 1.93 eV for high-bandgap TPSC (PMA: phenylmethylammonium). The addition of MA and Cs can help to improve phase separation but their film morphology and crystallinity were not good enough to enhance their device performances. The addition of PMA plays a pivotal role to form a quasi-2D structure not only on the surface of the perovskite but also in the bottom interface between perovskite and PEDOT:PSS based on the evidence obtained from XPS, SEM, GIWAXS and TOF-SIMS measurements. We found that PMA plays a key role to passivate the grain surface of perovskite and the interface between perovskite and hole-transport layer to give high performance (6.2%) and great stability for a wide-bandgap TPSC with a quadruple-cation configuration.
C.-H. Kuan, Y.-C. Chen, S. Narra, C.-F. Chang, Y.-W. Tsai, J.-M. Lin, G.-R. Chen, and Eric W.-G. Diau *, “Quadruple-Cation Wide-Bandgap Mixed-Halide Tin Perovskite Solar Cells”, ACS Energy Lett., 9, 2351−2357 (2024).