Bandgap Modulation of Cs2AgInX6 (X = Cl and Br) Double Perovskite Nano- and Microcrystals via Cu2+ Doping

Photocurrent Enhancement by Copper Incorporation in Chemical-Solution-Synthesized Inorganic Lead Perovskite Thin Films

Perovskite thin films are at the forefront of highly promising photovoltaic technologies due to their remarkable optoelectronic properties. Herein, we explore a low-cost, reproducible, and industry-scalable methodology to synthesize an all-inorganic CsPbI1.5Br1.5 perovskite thin film with additional incorporation of copper and chloride ions into the lattice structure. The synthesis process involves chemical bath deposition of PbS, followed by a gas-solid iodination reaction to yield PbI2. Subsequently, dip-coating incorporates Cs+, Cu2+, Br-, and Cl- ions into PbI2, and annealing at 270 °C produces perovskite thin films. The results show a large coverage area and a uniform thickness of each perovskite thin film. Comprehensive characterization, including X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and photoluminescence, provides the structural, chemical, and optical properties of the synthesized thin films. To evaluate the practical implications of our methodology, we fabricated photodetectors employing CsPbI1.5Br1.5 and (Cs0.95:Cu0.01)PbI1.5Br1.3Cl0.1 perovskite films. A comparative analysis unequivocally demonstrates a significant increase in photodetector performance when utilizing (Cs0.95:Cu0.01)PbI1.5Br1.3Cl0.1 perovskite films. While our findings quantitatively assess the tangible enhancement in photocurrent, we acknowledge the potential for improvement in device fabrication to enhance the overall performance. This study not only affirms the successful low-cost synthesis of perovskite thin films but also emphasizes the pivotal role of Cu2+ and Cl- ions in enhancing the performance of perovskite-based optoelectronic devices.

Bandgap reduction and efficiency enhancement in Cs2AgBiBr6 double perovskite solar cells through gallium substitution

Lead-free halide double perovskite (LFHDP) Cs2AgBiBr6 has emerged as a promising alternative to traditional lead-based perovskites (LBPs), offering notable advantages in terms of chemical stability and non-toxicity. However, the efficiency of Cs2AgBiBr6 solar cells faces challenges due to their wide bandgap (Eg). As a viable strategy to settle this problem, we consider optimization of the optical and photovoltaic properties of Cs2AgBiBr6 by Gallium (Ga) substitution. The synthesized Cs2Ag0.95Ga0.05BiBr6 is rigorously characterized by means of X-ray diffraction (XRD), UV-vis spectroscopy, and solar simulator measurements. XRD analysis reveals shifts in peak positions, indicating changes in the crystal lattice due to Ga substitution. The optical analysis demonstrates a reduction in the Eg, leading to improvement of the light absorption within the visible spectrum. Importantly, the Cs2Ag0.95Ga0.05BiBr6 solar cell exhibits enhanced performance, as evidenced by higher values of open circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF), which are 0.94 V, 6.01 mA cm-2, and 0.80, respectively: this results in an increased power conversion efficiency (PCE) from 3.51% to 4.52%. This research not only helps to overcome film formation challenges, but also enables stable Cs2Ag0.95Ga0.05BiBr6 to be established as a high-performance material for photovoltaic applications. Overall, our development contributes to the advancement of environmentally friendly solar technologies.

Integrated experimental and theoretical studies on structural and magnetic properties of thin films of double perovskite ruthenates: Ba2DyRuO6 & Sr2DyRuO6

Thin films of double perovskite ruthenates, viz., Ba2DyRuO6 (BDRO) and Sr2DyRuO6 (SDRO), have been successfully grown on a SrTiO3 substrate using the pulsed laser deposition technique. The BDRO samples crystallizes in cubic structure, while SDRO exhibits monoclinic structure as revealed in their X-Ray diffraction examination. Temperature-dependent magnetization measurements suggest the presence of ferromagnetism in BDRO, while paramagnetism is present for the SDRO thin film. Surprisingly, both films show canted antiferromagnetism at ∼T = 5 K as revealed in their isothermal magnetization curves. The inverse susceptibility has been fitted to the Curie-Weiss law for the SDRO sample, where the Curie temperature (TC ∼ -336.6 K) has been obtained, thus suggesting the prevalence of antiferromagnetic interactions. The existence of the canted magnetism at a lower temperature may be attributed to the Dzyaloshinskii-Moriya (D-M) interactions in the monoclinic SDRO sample due to structural distortion. However, the emergence of canted antiferromagnetism at lower temperatures (5 K) in the BDRO sample with cubic symmetry having no D-M interactions may be attributed to the various modifications at the surface of the thin films. Overall, a comparison made between the magnetic properties of both the thin films i.e., BDRO & SDRO, reveals the suppression of bulk magnetic ordering when compared to their bulk counterparts. The possible reason for the absence of any magnetic ordering in these thin films may be due to any modifications in superexchange interactions, any exchange bias, stress-strain, or uncompensated spins present in these types of thin films. UV-visible measurements for both the samples reveal a direct influence of the A-site element (Sr/Ba) on their band gaps, i.e., 3.66 eV and 2.59 eV for BDRO and SDRO samples, respectively, hence suggesting their insulating nature. We have also carried out first principles calculations with DFT using the CASTEP software to gain more insights into the experimental data. These thin films with insulating-antiferromagnetic properties may be crucial for "spintronics devices".

Triangulating Dopant-Level Mn(II) Insertion in a Cs2NaBiCl6 Double Perovskite Using Magnetic Resonance Spectroscopy

Lead-free metal halide double perovskites are gaining increasing attention for optoelectronic applications. Specifically, doping metal halide double perovskites using transition metals enables broadband tailorability of the optical bandgap for these emerging semiconducting materials. One candidate material is Mn(II)-doped Cs₂NaBiCl₆, but the nature of Mn(II) insertion on chemical structure is poorly understood due to low Mn loading. It is critical to determine the atomic-level structure at the site of Mn(II) incorporation in doped perovskites to better understand the structure-property relationships in these materials and thus to advance their applicability to optoelectronic applications. Magnetic resonance spectroscopy is uniquely qualified to address this, and thus a comprehensive three-pronged strategy, involving solid-state nuclear magnetic resonance (NMR), high-field dynamic nuclear polarization (DNP), and electron paramagnetic resonance (EPR) spectroscopies, is used to identify the location of Mn(II) insertion in Cs₂NaBiCl₆. Multinuclear (²³Na, ³⁵Cl, ¹³³Cs, and ²⁰⁹Bi) one-dimensional (1D) magnetic resonance spectra reveal a low level of Mn(II) incorporation, with select spins affected by paramagnetic relaxation enhancement (PRE) induced by Mn(II) neighbors. EPR measurements confirm the oxidation state, octahedral symmetry, and low doping levels of the Mn(II) centers. Complementary EPR and NMR measurements confirm that the cubic structure is maintained with Mn(II) incorporation at room temperature, but the structure deviates slightly from cubic symmetry at low temperatures (<30 K). HYperfine Sublevel CORrelation (HYSCORE) EPR spectroscopy explores the electron-nuclear correlations of Mn(II) with ²³Na, ¹³³Cs, and ³⁵Cl. The absence of ²⁰⁹Bi correlations suggests that Bi centers are replaced by Mn(II). Endogenous DNP NMR measurements from Mn(II) → ¹³³Cs (<30 K) reveal that the solid effect is the dominant mechanism for DNP transfer and supports that Mn(II) is homogeneously distributed within the double-perovskite structure.

Theoretical exploration of mechanical, electronic structure and optical properties of aluminium based double halide perovskite

The mechanical, electronic structure and optical properties of aluminium based double halide perovskite were calculated by density functional theory. The formation energy and elastic constant confirm the stability of the cubic perovskite materials. The materials are all ductile and suitable for flexible photovoltaic and optoelectronic devices. The band gap values vary from 0.773 eV to 3.430 eV, exactly corresponding to the range of ideal band gap values for good photoresponse. The band structure analysis shows that all the materials possess small effective mass, which indicates a good transport of carriers. And these materials have a broad energy range of optical absorption for utilization and a detector of photons. Moreover, less expensive K₂AgAlBr₆ were investigated for comparison with materials containing a cesium element, and according to the results, is also a candidate for photoelectronic devices due to the similar properties.

M₂AgAlX₆ (M = Cs, Rb and K, X = Cl, Br and I) is a stable vacancy ordered double halide perovskite direct band gap semiconductor material with good absorption of near-ultraviolet and short-wavelength visible light.