NSRRC Activity Report 2023

Energy Science 063 Recently, Wei-Guang Diau’s group at National Yang Ming Chiao Tung University utilized the GIWAXS technique in their perovskite solar cell (PSC) studies at TPS 25A . 1,2 PSCs are solar cells that utilize a perovskite-structured compound as a light adsorber. Originally, the CaTiO 3 crystalline structure was used; however, more recently the general perovskite structure ABX 3 is utilized, which comprises either a hybrid organic–inorganic or tin halide-based material. In comparison with silicon-based solar cells, the fabrication processes of PSCs use a relatively simple coating method and baking temperatures are generally under 150°C. The new series of pyrrolopyrrole-based polymers were synthesized as hole-transporting materials for Sn-based PSCs by Diau’s group. The GIWAXS patterns of the thin film samples showed good consistency with their X-ray diffraction data. The orientations of the tin-perovskite deposited on different hole-transporting polymers was almost isotropic. The research group also investigated the addition of different co-cations in the two-step fabrication of tin-based PSCs. An additional δ-phase (the tetragonal lattice) was observed from the normal cubic perovskite structure in GIWAXS patterns of specific co-cationic perovskite thin films. The GIWAXS technique at TPS 25A can directly assist the users in measuring crystalline properties of thin film devices. (Reported by Jhih-Min Lin) This report features the work of Wei-Guang Diau and his coworkers published in Adv. Mater. 35 , 2300681 (2023) and ACS Energ. Lett. 8 , 2423 (2023). TPS 25A Coherent X-ray Scattering • GISAXS, SAXS, WAXS • Materials Science, Batteries References 1. C.-H. Kuan, R. Balasaravanan, S.-M. Hsu, J.-S. Ni, Y.-T. Tsai, Z.-X. Zhang, M.-C. Chen, E. W.-G. Diau, Adv. Mater. 35 , 2300681 (2023). 2. C.-H. Kuan, Y.-A. Ko, E. W.-G. Diau, ACS Energ. Lett. 8 , 2423 (2023). Fig. 1 : (a) Raw GIWAXS pattern; (b) GIWAXS pattern with pole figure correction. [Reproduced from Ref. 1] Revealing the Key Elements of Energy Storing The charge/discharge mechanism in electrode material of batteries is discussed from the perspectives of X-ray absorption fine structure. X -ray absorption fine structure (XAFS) spectroscopy is a powerful technique to investigate the physical and chemical characteristics of materials. XAFS can be divided into X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The spectral energy region nearing the absorption edge of an absorbing atom is referred to as XANES and the oscillation features which extend for 1,000 eV or more above the absorption edge, are referred to as EXAFS. The XANES spectrum exhibits high sensitivity to oxidation and geometry, while the EXAFS region depends on radial distribution of electron density surrounding the absorbing atom. This allows XAFS spectroscopy to be used as a quantitative method for determining bond length and coordination number. So far, this technique has been widely applied to several scientific research fields, including battery development and catalysis. The development of battery technology has become increasingly innovative alongside the rapidly expanding market for rechargeable electric vehicles. Creating novel battery types or improving existing ones remain a challenge. For instance, batteries which work through redox reactions of the electrodes may be accompanied