Black orthorhombic (B-γ) CsSnI3 with reduced biotoxicity and environmental impact and excellent optoelectronic properties is being considered as a promising eco-friendly candidate for high-performing perovskite solar cells (PSCs). A major challenge in a large-scale implementation of CsSnI3 PSCs includes the rapid transformation of Sn2+ to Sn4+ (within a few minutes) under an ambient-air condition. Here, we demonstrate that ambient-air stable B-γ CsSnI3 PSCs can be fabricated by incorporating N,N′-methylenebis­(acrylamide) (MBAA) into the perovskite layer and by using poly­(3-hexylthiophene) as the hole transporting material. The lone electron pairs of −NH and −CO units of MBAA are designed to form coordination bonding with Sn2+ in the B-γ CsSnI3, resulting in a reduced defect (Sn4+) density and better stability under multiple conditions for the perovskite light absorber. After a modification, the highest power conversion efficiency (PCE) of 7.50% is documented under an ambient-air condition for the unencapsulated CsSnI3-MBAA PSC. Furthermore, the MBAA-modified devices sustain 60.2%, 76.5%, and 58.4% of their initial PCEs after 1440 h of storage in an inert condition, after 120 h of storage in an ambient-air condition, and after 120 h of 1 Sun continuous illumination, respectively.

Although unprecedented conversion efficiency has been achieved in organic–inorganic hybrid perovskite solar cells (PSCs), their long‐term stability has remained a major issue in their transition. Here, we demonstrate a highly‐stable CH3NH3PbI3 (MAPbI3) perovskite using a green self‐assembly (SA) process that provides a major breakthrough in resolving this issue. In this process, the hydrophobic polymer, poly(methyl methacrylate) (PMMA), is introduced into the 2D layered MAPbI3 perovskite intermediates, resulting in chemical coordination and self‐assembly into 3D perovskite grains with PMMA coated along the grain boundaries. The bilayer grain boundary effectively blocks moisture corrosion thereby significantly improving the stability of MAPbI3 perovskite. Further, PMMA is found to reduce the trap density by electronically compensating the iodide vacancy along the boundary, which decreases the charge recombination and improves the open circuit voltage of PSCs. The PSCs comprising the MAPbI3−PMMA layer show excellent stability under high moisture conditions, exhibiting no phase change under ≈70% humidity for over 31 days (approximately 500% higher compared to state‐of‐the‐art) and excellent performance in 50–70% humidity for over 50 days.

In high magnetic fields, two-dimensional electron systems can form a number of phases in which interelectron repulsion plays the central role, since the kinetic energy is frozen out by Landau quantization. These phases include the well-known liquids of the fractional quantum Hall effect, as well as solid phases with broken spatial symmetry and crystalline order. Solids can occur at the low Landau-filling termination of the fractional quantum Hall effect series but also within integer quantum Hall effects. Here we present microwave spectroscopy studies of wide quantum wells that clearly reveal two distinct solid phases, hidden within what in d.c. transport would be the zero diagonal conductivity of an integer quantum-Hall-effect state. Explanation of these solids is not possible with the simple picture of a Wigner solid of ordinary (quasi) electrons or holes.

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Photoluminescence (PL) spectroscopy of nonpolar m-plane InGaN thin films with indium composition up to 21% and nearly strain-balanced In0.09Ga0.91N/Al0.19Ga0.81N superlattices grown by plasma-assisted molecular beam epitaxy was performed as a function of temperature. The experimental transition energies are consistently lower than the calculation based on structural parameters extracted from x-ray diffraction measurements. This indicates the presence of indium composition fluctuations in InGaN and hence local bandgap reduction that produces charge localization centers. The spectral width of the low-temperature PL of our m-plane InGaN/AlGaN superlattices is narrower than previously reported for m-plane InGaN/GaN quantum wells grown by MOCVD. The PL integrated intensity drops rapidly, though, as the temperature is increased to 300 K, indicating strong non-radiative recombination at room temperature. Time-resolved PL at low temperatures was performed to characterize the relaxation time scales in an undoped and a doped superlattice.