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Interfacial phenomena critically influence both the performance and long-term stability of perovskite solar cells; hence, optimizing interfaces remains a key challenge for their commercialization. In this study, we investigate the chemical interactions and electronic structure of the buried interface between the FAPbI₃ perovskite absorber and spiro-OMeTAD-based hole transport layer (HTL) in an ITO/SnO₂/FAPbI₃/HTL device using hard X-ray photoelectron spectroscopy. Our results indicate Pb and I ion incorporation in the spiro-OMeTAD HTL. The Pb 4f core level spectra show the formation of new nonperovskite Pb species, and the N 1s spectra exhibit an additional peak, indicating chemical modifications induced by the deposition of spiro-OMeTAD on the perovskite layer. Moreover, the spiro-OMeTAD N 1s peak exhibits a systematic shift toward lower binding energies with increasing HTL thickness, indicating a downward band bending in the spiro-OMeTAD HTL. Overall, these findings provide direct insight into the chemical and electronic interactions near the FAPbI₃/HTL interface and emphasize the importance of optimizing transport layer thickness to achieve favorable energy level alignment and improved device performance.

Electrochemical water splitting is an eco-friendly method for large-scale production of high-purity hydrogen (H2) and oxygen (O2), and hence, pioneering the design of efficient and economic bifunctional electrocatalysts is necessary. Here, hexagonal (Cu,Co)Se2 nanoflakes are fabricated to leverage the unique synergy between copper and cobalt for efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). As HER and OER catalysts, (Cu,Co)Se2 nanoflakes demonstrate low overpotentials of 104 and 250 mV, respectively, to reach current densities of 10 mA cm-2 in 1 m KOH solution, with respective Tafel slopes of 117.7 and 61 mV dec-1. The catalyst requires only 403 mV of overpotential to reach 1000 mA cm-2 in OER. XANES analyses reveal average oxidation states of Co as 2.6+ and 3+ post-HER and post-OER, respectively, while Cu remains predominantly in 2+ states. Presence of Cu around Co induces orbital rehybridization through linking Se bonds; establishing a cooperative participation between Co and Cu to facilitate overall charge-transfer processes, eventually enhancing catalytic activity of (Cu,Co)Se2. Further, (Cu,Co)Se2/NF-based overall-water-splitting electrolyzer offers low cell voltage (1.65V at 10 mA cm-2) and high durability even at a high current density (at eta 50) in 1 m KOH, thus demonstrating its commercial application prospects.

Tin oxide (SnO x ) by atomic-layer deposition (ALD), in combination with fullerene, is widely employed as an electron transport layer in p-i-n perovskite solar cells. This study investigates the direct deposition of ALD SnO x on top of formamidinium (FA)-based perovskites, as a step toward the elimination of the fullerene interlayer and its poor effect on solar cell's long-term stability. The interfacial chemistry between FA-based perovskites (FAPbI3 and FAPbBr3) and ALD SnO x was studied using soft and hard X-ray photoelectron spectroscopy (SOXPES and HAXPES) with a focus on investigating the separate roles FA and different halides play during interface formation. FAPbI3 and FAPbBr3 solar cell structures solely containing ALD SnO x resulted in s-shaped current-voltage characteristics, indicating the formation of a transport barrier at the interface. Both SOXPES and HAXPES measurements revealed the emergence of additional nitrogen states at the interface during the ALD SnO x deposition on FAPbI3 and FAPbBr3, where these states are linked to the decomposition of FA+. The FAPbI3/ALD SnO x interface also showed the presence of lead iodide (PbI2) through additional lead states other than that from FAPbI3 by using SOXPES measurements. Concerning the FAPbBr3/ALD SnO x interface, no additional lead states were observed; however, measurements instead revealed the formation of Sn-Br bonds at the interface along with the migration of bromine ions into the bulk of the ALD SnO x . Thus, FAPbI3 and FAPbBr3 undergo distinct reaction pathways upon direct deposition of ALD SnO x on top of them. We reason that the decomposition of FA+ in both perovskites and the formation of PbI2 at the FAPbI3/ALD SnO x interface and the incorporation of Br in SnO x at the FAPbBr3/ALD SnO x interface prove detrimental toward device performance. Therefore, careful interfacial engineering that can mitigate the formation of these products should be utilized to enhance the performance of perovskite solar cells.

To commercialize lead halide perovskites as light-emitting diodes (LEDs), the operational device lifetime needs to be drastically improved. For this to be achieved, an understanding of degradation behavior under bias is crucial. Herein, we perform operando measurements of the structural, chemical, and electronic changes using synchrotron-based grazing-incidence wide-angle X-ray scattering and hard X-ray photoelectron spectroscopy on full-stack deep blue mixed bromide/chloride lead halide perovskite LEDs. While a clear drop in optoelectronic performance is recorded under electrical bias, the accompanying X-ray scattering data reveals only minor changes in structural properties. However, photoelectron spectroscopy reveals substantial chemical changes at the electron-injecting interface after bias is applied, including the formation of unwanted metallic lead and a new chlorine species that is not in the perovskite structure. These operando approaches give important structural and interfacial perspectives to reveal the degradation mechanisms in these LEDs and highlight the need to address the top electron-injecting interface to realize step-changes in operational stability.