Even though solution‐processed Cu(In,Ga)(S,Se)2 (CIGSSe) solar cells have been developed for long time, their power conversion efficiency (PCE) is still much behind that achieved by vacuum‐based process, and some solvents used in solution‐based processes are not environmental friendly. High‐efficiency CIGSSe solar cells made by using water‐based spray deposition in an air environment are reported. Water is the most eco‐friendly and cheapest solvent compared to the other solvents used in solution‐based fabrication. In2S3‐based buffer (eco‐friendly Cd‐free buffer) and CdS buffer are tested as a buffer layer. For higher PCE with In2S3‐based buffer, a Zr4+‐alloyed In2S3 is used and Zr4+ alloying effects are investigated. It is found that Zr4+ alloying increases the electron concentration in the buffer and passivates defect states in the CIGSSe absorber, which enhance PCE significantly. On the other hand, it is found that K‐alloying into the CIGSSe absorber passivates defects in the CIGSSe absorber, which further increases PCE. Owing to the observed beneficial effects, highest PCE of 16.08% and 17.74% is achieved with Zr4+‐In2S3 buffer and CdS buffer, respectively. In addition, since fabricated solar cells are made with bandgap below 1.15 eV, they can be utilized as a bottom cell for high efficiency tandem cell.

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Garnet Li7La3Zr2O12 (LLZO) is a promising solid electrolyte for all-solid-state Li-ion batteries because of its outstanding performance. However, LLZO exists in two polymorphic phases, tetragonal (∼10–3 mS cm–1) and cubic (1-10–1 mS cm–1), where the cubic phase exhibits higher Li-ion conductivity but is thermodynamically unstable at ambient room temperature. To stabilize the cubic phase with high ionic conductivity, we fabricated mono- and codoped garnet with Ta5+ and Ga3+ (Li7–3x–z=6.4Ga x La3Zr2–z Ta z O12) and investigated the doping effects. The doping effects on the crystal structure and ionic conductivity were systematically investigated using X-ray diffraction, Raman scattering, scanning electron microscopy, alternative current (AC) impedance, and direct current (DC) polarization methods. The characterization results revealed that Ta-doping favors higher occupation of Li-ions on the mobile octahedral (LiO6) site and improves ionic conductivity of the grain boundary. However, it showed poor total ionic conductivity (2.044 × 10–4 S cm–1 at 1100 °C for 12 h) due to the low sinterability [relative density (RD): ∼80.3%]. On the other hand, Ga-doping provides better sinterability (RD: ∼93.1%) and bulk conductivity. Considering the beneficial effects of Ga- and Ta-doping, codoped Li6.4Ga0.133La3Zr1.8Ta0.2O12 garnet with enhanced ionic conductivity (6.141 × 10–4 S cm–1) and improved high-density microstructure (RD: ∼95.7%) was obtained.

Organic systems often allow to create two triplet spin states (triplet excitons) by converting an initially excited singlet spin state (a singlet exciton). An ideally designed organic/inorganic heterostructure could reach the photovoltaic energy harvest over the Shockley-Queisser (S-Q) limit because of the efficient conversion of triplet excitons into charge carriers. Here, we demonstrate the molybdenum ditelluride (MoTe 2 )/pentacene heterostructure to boost the carrier density via efficient triplet transfer from pentacene to MoTe 2 using ultrafast transient absorption spectroscopy. We observe carrier multiplication by nearly four times by doubling carriers in MoTe 2 via the inverse Auger process and subsequently doubling carriers via triplet extraction from pentacene. We also verify efficient energy conversion by doubling the photocurrent in the MoTe 2 /pentacene film. This puts a step forward to enhancing photovoltaic conversion efficiency beyond the S-Q limit in the organic/inorganic heterostructures.

With the growing need for cost-effective and sustainable Internet of things (IoT) technologies, kesterite-based solar cells are gaining popularity. We report the fabrication of an efficient CZTSSe absorber layer with...