In Situ Polymerization of Cross-Linked Perovskite–Polymer Composites for Highly Stable and Efficient Perovskite Solar Cells

Mixed-halide perovskites have emerged as outstanding light absorbers that enable the fabrication of efficient solar cells; however, their instability hinders the commercialization of such systems. Grain-boundary (GB) defects and lattice tensile strain are critical intrinsic-instability factors in polycrystalline perovskite films. In this study, the light-induced cross-linking of acrylamide (Am) monomers with non-crystalline perovskite films is used to fabricate highly efficient and stable perovskite solar cells (PSCs). The Am monomers induce the preferred crystal orientation in the polycrystalline perovskite films, enlarge the perovskite grain size, and cross-link the perovskite grains. Additionally, the liquid properties of Am effectively releases lattice strain during perovskite-film crystallization. The cross-linked interfacial layer functions as an airtight wall that protects the perovskite film from water corrosion. Devices fabricated using the proposed strategy show an excellent power conversion efficiency (PCE) of 24.45% with an open-circuit voltage (V_OC) of 1.199 V, which, to date, is the highest V_OC reported for hybrid PSCs with electron transport layers (ETLs) comprised of TiO₂. Large-area PSC modules fabricated using the proposed strategy show a power conversion efficiency of 20.31% (with a high fill factor of 77.1%) over an active area of 33 cm², with excellent storage stability.     

Is Excess PbI2 Beneficial for Perovskite Solar Cell Performance?

Unreacted lead iodide is commonly believed to be beneficial to the efficiency of methylammonium lead iodide perovskite based solar cells, since it has been proposed to passivate the defects in perovskite grain boundaries. However, it is shown here that the presence of unreacted PbI₂ results in an intrinsic instability of the film under illumination, leading to the film degradation under inert atmosphere and faster degradation upon exposure to illumination and humidity. The perovskite films without lead iodide have improved stability, but lower efficiency due to inferior film morphology (smaller grain size, the presence of pinholes). Optimization of the deposition process resulted in PbI₂‐free perovskite films giving comparable efficiency to those with excess PbI₂ (14.2 ± 1.3% compared to 15.1 ± 0.9%) Thus, optimization of the deposition process for PbI₂‐free films leads to dense, pinhole‐free, large grain size perovskite films which result in cells with high efficiency without detrimental effects on the film photostability caused by excess PbI₂. However, it should be noted that for encapsulated devices illuminated through the substrate (fluorine‐doped tin oxide glass, TiO₂ film), film photostability is not a key factor in the device degradation.     

Efficient and Stable Tin–Lead Perovskite Photoconversion Devices Using Dual-Functional Cathode Interlayer

Tin–lead halide perovskites (TLHPs) are promising photoactive materials for photovoltaics (PVs) due to reduced toxicity and broad light absorption. However, their inherent ionic vacancies facilitate inward metal diffusion, accelerating device degradation. Here, efficient, stable TLHP-based PV and photoelectrochemical (PEC) devices are reported containing a chemically protective cathode interlayer—amine-functionalized perylene diimide (PDINN). Solution-processed PDINN effectively extract electrons and suppress inward-metal diffusion by forming tridentate metal complexes with its nucleophilic sites. The PV device achieved an efficiency of 23.21% (>81% retention after 750 h at 60 °C and >90% retention after 3100 h at 23 ± 4 °C), and the first demonstration of TLHP-based PEC devices exhibit a record-high bias-free solar hydrogen production rate (33.0 mA cm⁻²; ≈3.42 × 10⁻⁶ kg s⁻¹ m⁻²) when coupled with biomass oxidation, which is ≈1.7-fold higher than the ultimate target set by the U.S. Department of Energy for one-sun hydrogen production. These findings demonstrate the potential of TLHPs for efficient, stable photoconversion by the molecular design of the cathode interlayer.     

R. D. Fitzgerald's F. L. S. „Australian Orchids“

Ohne Zusammenfassung     

Why are Hot Holes Easier to Extract than Hot Electrons from Methylammonium Lead Iodide Perovskite?

Charge‐carriers photoexcited above a semiconductor's bandgap rapidly thermalize to the band‐edge. The cooling of these difficult to collect “hot” carriers caps the available photon energy that solar cells–including efficient perovskite solar cells–may utilize. Here, the dynamics and efficiency of hot carrier extraction from MAPbI₃ (MA = methylammonium) perovskite by spiro‐OMeTAD (a hole‐transporting layer) and TiO₂ (an electron‐transporting layer) are investigated and explained using both ultrafast electronic spectroscopy and theoretical modeling. Time‐resolved spectroscopy reveals a quasi‐equilibrium distribution of hot carriers forming upon excess‐energy excitation of the perovskite–a distribution largely unaffected by the presence of TiO₂. In contrast, the quasi‐equilibrium distribution of hot carriers is virtually nonexistent when spiro‐OMeTAD is present, which is indicative of efficient hot hole extraction at the interface of MAPbI₃. Density functional theory calculations predict that deep energy‐levels of MAPbI₃ exhibit electronically delocalized character, with significant overlap with the localized valence band charge of the spiro‐OMeTAD molecules lying on the surface of MAPbI₃. Consequently, hot holes are easily extracted from the deep energy‐levels of MAPbI₃ by spiro‐OMeTAD. These findings uncover the origins of efficient hot hole extraction in perovskites and offer a practical blueprint for optimizing solar cell interlayers to enable hot carrier utilization.