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Abstract The combined effects of compact TiO₂(c‐TiO₂) electron‐transport layer (ETL) are investigated without and with mesoscopic TiO₂(m‐TiO₂) on top, and without and with an iodine‐terminated silane self‐assembled monolayer (SAM), on the mechanical behavior, opto–electronic properties, photovoltaic (PV) performance, and operational‐stability of solar cells based on metal‐halide perovskites (MHPs). The interfacial toughness increases almost threefold in going from c‐TiO₂without SAM to m‐TiO₂with SAM. This is attributed to the synergistic effect of the m‐TiO₂/MHP nanocomposite at the interface and the enhanced adhesion afforded by the iodine‐terminated silane SAM. The combination of m‐TiO₂and SAM also offers a significant beneficial effect on the photocarriers extraction at the ETL/MHP interface, resulting in perovskite solar cells (PSCs) with power‐conversion efficiency (PCE) of over 24% and 20% for 0.1 and 1 cm²active areas, respectively. These PSCs also have exceptionally long operational‐stability lives: extrapolatedT80 (duration at 80% initial PCE retained) is ≈18 000 and 10 000 h for 0.1 and 1 cm²active areas, respectively.Postmortemcharacterization and analyses of the operational‐stability‐tested PSCs are performed to elucidate the possible mechanisms responsible for the long operational‐stability. 

Abstract Two key interfaces in flexible perovskite solar cells (f‐PSCs) are mechanically reinforced simultaneously: one between the electron‐transport layer (ETL) and the 3D metal‐halide perovskite (MHP) thin film using self‐assembled monolayer (SAM), and the other between the 3D‐MHP thin film and the hole‐transport layer (HTL) using an in situ grown low‐dimensional (LD) MHP capping layer. The interfacial mechanical properties are measured and modeled. This rational interface engineering results in the enhancement of not only the mechanical properties of both interfaces but also their optoelectronic properties holistically. As a result, the new class of dual‐interface‐reinforced f‐PSCs has an unprecedented combination of the following three important performance parameters: high power‐conversion efficiency (PCE) of 21.03% (with reduced hysteresis), improved operational stability of 1000 hT₉₀(duration at 90% initial PCE retained), and enhanced mechanical reliability of 10 000 cyclesn₈₈(number of bending cycles at 88% initial PCE retained). The scientific underpinnings of these synergistic enhancements are elucidated. 

Abstract State‐of‐the‐art perovskite solar cells (PSCs) have bandgaps that are invariably larger than 1.45 eV, which limits their theoretically attainable power conversion efficiency. The emergent mixed‐(Pb, Sn) perovskites with bandgaps of 1.2–1.3 eV are ideal for single‐junction solar cells according to the Shockley–Queisser limit, and they have the potential to deliver higher efficiency. Nevertheless, the high chemical activity of Sn(II) in these perovskites makes it extremely challenging to control their physical properties and chemical stability, thereby leading to PSCs with relatively low PCE and stability. In this work, the authors employ the Lewis‐adduct SnF₂·3FACl additive in the solution‐processing of ideal‐bandgap halide perovskites (IBHPs), and prepare uniform large‐grain perovskite thin films containing continuously functionalized grain boundaries with the stable SnF₂phase. Such Sn(II)‐rich grain‐boundary networks significantly enhance the physical properties and chemical stability of the IBHP thin films. Based on this approach, PSCs with an ideal bandgap of 1.3 eV are fabricated with a promising efficiency of 15.8%, as well as enhanced stability. The concept of Lewis‐adduct‐mediated grain‐boundary functionalization in IBHPs presented here points to a new chemical route for approaching the Shockley–Queisser limit in future stable PSCs. 

Sn‐based perovskites are promising Pb‐free photovoltaic materials with an ideal 1.3 eV bandgap. However, to date, Sn‐based thin film perovskite solar cells have yielded relatively low power conversion efficiencies (PCEs). This is traced to their poor photophysical properties (i.e., short diffusion lengths (<30 nm) and two orders of magnitude higher defect densities) than Pb‐based systems. Herein, it is revealed that melt‐synthesized cesium tin iodide (CsSnI₃) ingots containing high‐quality large single crystal (SC) grains transcend these fundamental limitations. Through detailed optical spectroscopy, their inherently superior properties are uncovered, with bulk carrier lifetimes reaching 6.6 ns, doping concentrations of around 4.5 × 10¹⁷cm⁻³, and minority‐carrier diffusion lengths approaching 1 µm, as compared to their polycrystalline counterparts having ≈54 ps, ≈9.2 × 10¹⁸cm⁻³, and ≈16 nm, respectively. CsSnI₃SCs also exhibit very low surface recombination velocity of ≈2 × 10³cm s⁻¹, similar to Pb‐based perovskites. Importantly, these key parameters are comparable to high‐performance p‐type photovoltaic materials (e.g., InP crystals). The findings predict a PCE of ≈23% for optimized CsSnI₃SCs solar cells, highlighting their great potential. 

Abstract Formamidinium (FA)‐based lead iodide perovskites have emerged as the most promising light‐absorber materials in the prevailing perovskite solar cells (PSCs). However, they suffer from the phase‐instability issue in the ambient atmosphere, which is holding back the realization of the full potential of FA‐based PSCs in the context of high efficiency and stability. Herein, the tetraethylorthosilicate hydrolysis process is integrated with the solution crystallization of FA‐based perovskites, forming a new film structure with individual perovskite grains encapsulated by amorphous silica layers that are in situ formed at the nanoscale. The silica not only protects perovskite grains from the degradation but also enhances the charge‐carrier dynamics of perovskite films. The underlying mechanism is discussed using a joint experiment‐theory approach. Through this in situ grain encapsulation method, PSCs show an efficiency close to 20% with an impressive 97% retention after 1000‐h storage under ambient conditions.