Light-induced structural dynamics plays a vital role in the physical properties, device performance, and stability of hybrid perovskite-based optoelectronic devices. We report that continuous light ...illumination leads to a uniform lattice expansion in hybrid perovskite thin films, which is critical for obtaining high-efficiency photovoltaic devices. Correlated, in situ structural and device characterizations reveal that light-induced lattice expansion benefits the performances of a mixed-cation pure-halide planar device, boosting the power conversion efficiency from 18.5 to 20.5%. The lattice expansion leads to the relaxation of local lattice strain, which lowers the energetic barriers at the perovskite-contact interfaces, thus improving the open circuit voltage and fill factor. The light-induced lattice expansion did not compromise the stability of these high-efficiency photovoltaic devices under continuous operation at full-spectrum 1-sun (100 milliwatts per square centimeter) illumination for more than 1500 hours.
Achieving technologically relevant performance and stability for optoelectronics, energy conversion, photonics, spintronics and quantum devices requires creating atomically precise materials with ...tailored homo- and hetero-interfaces, which can form functional hierarchical assemblies. Nature employs tunable sequence chemistry to create complex architectures, which efficiently transform matter and energy, however, in contrast, the design of synthetic materials and their integration remains a long-standing challenge. Organic-inorganic two-dimensional halide perovskites (2DPKs) are organic and inorganic two-dimensional layers, which self-assemble in solution to form highly ordered periodic stacks. They exhibit a large compositional and structural phase space, which has led to novel and exciting physical properties. In this Review, we discuss the current understanding in the structure and physical properties of 2DPKs from the monolayers to assemblies, and present a comprehensive comparison with conventional semiconductors, thereby providing a broad understanding of low-dimensional semiconductors that feature complex organic-inorganic hetero-interfaces.
Ruddlesden-Popper halide perovskites are 2D solution-processed quantum wells with a general formula A
A'
M
X
, where optoelectronic properties can be tuned by varying the perovskite layer thickness ...(n-value), and have recently emerged as efficient semiconductors with technologically relevant stability. However, fundamental questions concerning the nature of optical resonances (excitons or free carriers) and the exciton reduced mass, and their scaling with quantum well thickness, which are critical for designing efficient optoelectronic devices, remain unresolved. Here, using optical spectroscopy and 60-Tesla magneto-absorption supported by modeling, we unambiguously demonstrate that the optical resonances arise from tightly bound excitons with both exciton reduced masses and binding energies decreasing, respectively, from 0.221 m
to 0.186 m
and from 470 meV to 125 meV with increasing thickness from n equals 1 to 5. Based on this study we propose a general scaling law to determine the binding energy of excitons in perovskite quantum wells of any layer thickness.
State‐of‐the‐art light‐emitting diodes (LEDs) are made from high‐purity alloys of III–V semiconductors, but high fabrication cost has limited their widespread use for large area solid‐state lighting. ...Here, efficient and stable LEDs processed from solution with tunable color enabled by using phase‐pure 2D Ruddlesden–Popper (RP) halide perovskites with a formula (CH3(CH2)3NH3)2(CH3NH3)n−1PbnI3n+1 are reported. By using vertically oriented thin films that facilitate efficient charge injection and transport, efficient electroluminescence with a radiance of 35 W Sr−1 cm−2 at 744 nm with an ultralow turn‐on voltage of 1 V is obtained. Finally, operational stability tests suggest that phase purity is strongly correlated to stability. Phase‐pure 2D perovskites exhibit >14 h of stable operation at peak operating conditions with no droop at current densities of several Amperes cm−2 in comparison to mixtures of 2D/3D or 3D perovskites, which degrade within minutes.
Phase‐pure Ruddlesden–Popper layered perovskites (RPLPs) are investigated for light‐emitting diode application. This work demonstrates that RPLPs represent a promising candidate for optoeletronics and the crystal orientation of RPLPs plays a vital role in light‐emitting diode devices, resulting in external quantum efficiency ≈1% with ultralow turn‐on voltage.
State-of-the-art photovoltaics use high-purity, large-area, wafer-scale single-crystalline semiconductors grown by sophisticated, high-temperature crystal growth processes. We demonstrate a ...solution-based hot-casting technique to grow continuous, pinhole-free thin films of organometallic perovskites with millimeter-scale crystalline grains. We fabricated planar solar cells with efficiencies approaching 18%, with little cell-to-cell variability. The devices show hysteresis-free photovoltaic response, which had been a fundamental bottleneck for the stable operation of perovskite devices. Characterization and modeling attribute the improved performance to reduced bulk defects and improved charge carrier mobility in large-grain devices. We anticipate that this technique will lead the field toward synthesis of wafer-scale crystalline perovskites, necessary for the fabrication of high-efficiency solar cells, and will be applicable to several other material systems plagued by polydispersity, defects, and grain boundary recombination in solution-processed thin films.
Hybrid perovskites are on a trajectory toward realizing the most efficient single‐junction, solution‐processed photovoltaic devices. However, a critical issue is the limited understanding of the ...correlation between the degree of crystallinity and the emergent perovskite/hole (or electron) transport layer on device performance and photostability. Here, the controlled growth of hybrid perovskites on nickel oxide (NiO) is shown, resulting in the formation of thin films with enhanced crystallinity with characteristic peak width and splitting reminiscent of the tetragonal phase in single crystals. Photophysical and interface sensitive measurements reveal a reduced trap density at the perovskite/NiO interface in comparison with perovskites grown on poly(3,4‐ethylene dioxy thiophene) polystyrene sulfonate. Photovoltaic cells exhibit a high open circuit voltage (1.12 V), indicating a near‐ideal energy band alignment. Moreover, photostability of photovoltaic devices up to 10‐Suns is observed, which is a direct result of the superior crystallinity of perovskite thin films on NiO. These results elucidate the critical role of the quality of the perovskite/hole transport layer interface in rendering high‐performance and photostable optoelectronic devices.
Highly crystalline perovskite thin film can be grown on nickel oxide substrates evidenced by sharp X‐ray diffraction pattern with characteristic tetragonal peak splitting observed only in single crystal. As a consequence, high‐efficiency photovoltaic cells can be achieved with extended operation lifetime under constant illumination benefit by the high degree of crystallinity.
2D Ruddlesden–Popper (RP) perovskites have recently emerged as promising candidates for hybrid perovskite photovoltaic cells, realizing power‐conversion efficiencies (PCEs) of over 10% with ...technologically relevant stability. To achieve solar cell performance comparable to the state‐of‐the‐art 3D perovskite cells, it is highly desirable to increase the conductivity and lower the optical bandgap for enhanced near‐IR region absorption by increasing the perovskite slab thickness. Here, the use of the 2D higher member (n = 5) RP perovskite (n‐butyl‐NH3)2(MeNH3)4Pb5I16 in depositing highly oriented thin films from dimethylformamide/dimethylsulfoxide mixtures using the hot‐casting method is reported. In addition, they exhibit superior environmental stability over thin films of their 3D counterpart. These films are assembled into high‐efficiency solar cells with an open‐circuit voltage of ≈1 V and PCE of up to 10%. This is achieved by fine‐tuning the solvent ratio, crystal growth orientation, and grain size in the thin films. The enhanced performance of the optimized devices is ascribed to the growth of micrometer‐sized grains as opposed to more typically obtained nanometer grain size and highly crystalline, densely packed microstructures with the majority of the inorganic slabs preferentially aligned out of plane to the substrate, as confirmed by X‐ray diffraction and grazing‐incidence wide‐angle X‐ray scattering mapping.
Controllable tuning of the thin film properties of high‐n member layered Ruddlesden–Popper perovskites, BA2MA4Pb5I16, is achieved via a hot‐casting method using dimethylformamide (DMF)/dimethylsulfoxide (DMSO) processing solvent. Unlike the polycrystalline films grown from DMF, the optimized 3:1 DMF:DMSO films are essentially single‐crystalline with regularly stacked inorganic slabs, and deliver solar cell power conversion efficiencies up to 10%.
2D perovskites are a class of halide perovskites offering a pathway for realizing efficient and durable optoelectronic devices. However, the broad chemical phase space and lack of understanding of ...film formation have led to quasi‐2D perovskite films with polydispersity in perovskite layer thicknesses, which have hindered device performance and stability. Here, a simple and scalable approach is reported, termed as the “phase‐selective method”, to fabricate 2D perovskite thin films with homogenous layer thickness (phase purity). The phase‐selective method involves the dissolution of single‐crystalline powders with a homogeneous perovskite layer thickness in desired solvents to fabricate thin films. In situ characterizations reveal the presence of sub‐micrometer‐sized seeds in solution that preserve the memory of the dissolved single crystals and dictate the nucleation and growth of grains with an identical thickness of the perovskite layers in thin films. Photovoltaic devices with a p–i–n architecture are fabricated with such films, which yield an efficiency of 17.1% enabled by an open‐circuit voltage of 1.20 V, while preserving 97.5% of their peak performance after 800 h under illumination without any external thermal management.
Fabrication of phase‐pure films of 2D perovskites using a novel, simple, and scalable method, referred to as the phase‐selective method, is demonstrated. Phase‐purity is enabled by the presence of sub‐micrometer‐sized seeds in the precursor‐solution that preserves the memory of the dissolved single‐crystals. A photovoltaic efficiency of 17.1% with a VOC of 1.20 V and stability T97.5 = 800 h at MPP is reported.
Three-dimensional organic-inorganic perovskites have emerged as one of the most promising thin-film solar cell materials owing to their remarkable photophysical properties, which have led to power ...conversion efficiencies exceeding 20 per cent, with the prospect of further improvements towards the Shockley-Queisser limit for a single‐junction solar cell (33.5 per cent). Besides efficiency, another critical factor for photovoltaics and other optoelectronic applications is environmental stability and photostability under operating conditions. In contrast to their three-dimensional counterparts, Ruddlesden-Popper phases--layered two-dimensional perovskite films--have shown promising stability, but poor efficiency at only 4.73 per cent. This relatively poor efficiency is attributed to the inhibition of out-of-plane charge transport by the organic cations, which act like insulating spacing layers between the conducting inorganic slabs. Here we overcome this issue in layered perovskites by producing thin films of near-single-crystalline quality, in which the crystallographic planes of the inorganic perovskite component have a strongly preferential out-of-plane alignment with respect to the contacts in planar solar cells to facilitate efficient charge transport. We report a photovoltaic efficiency of 12.52 per cent with no hysteresis, and the devices exhibit greatly improved stability in comparison to their three-dimensional counterparts when subjected to light, humidity and heat stress tests. Unencapsulated two-dimensional perovskite devices retain over 60 per cent of their efficiency for over 2,250 hours under constant, standard (AM1.5G) illumination, and exhibit greater tolerance to 65 per cent relative humidity than do three-dimensional equivalents. When the devices are encapsulated, the layered devices do not show any degradation under constant AM1.5G illumination or humidity. We anticipate that these results will lead to the growth of single-crystalline, solution-processed, layered, hybrid, perovskite thin films, which are essential for high-performance opto-electronic devices with technologically relevant long-term stability.
Layered hybrid organic–inorganic perovskites (HOPs) have re-emerged as potential technological solutions for next-generation photovoltaic and optoelectronic applications. Their two-dimensional (2D) ...nature confers them a significant flexibility and results in the appearance of quantum and dielectric confinements. Such confinements are at the origin of their fascinating properties, and understanding them from a fundamental level is of paramount importance for optimization. Here, we provide an in-depth investigation of band alignments of 2D HOP allowing access to carriers’ confinement potentials. 2D HOPs are conceptualized as composite materials in which pseudoinorganic and -organic components are defined. In this way, computational modeling of band alignments becomes affordable using first-principles methods. First, we show that the composite approach is suitable to study the position-dependent dielectric profiles and enables clear differentiation of the respective contributions of inorganic and organic components. Then we apply the composite approach to a variety of 2D HOPs, assessing the impact on the confinement potentials of well and barrier thickness, of the nature of the inorganic well, and of structural transitions. Using the deduced potentials, we further discuss the limitations of the effective mass approximation, scrutinizing the electronic properties of this family of composite materials. Our simulations demonstrate type-I dominant band alignment in 2D HOPs. Finally, we outline design principles on band alignment toward achieving specific optoelectronic properties. Thus, we present alternative theoretical methods to inspect the properties of 2D hybrid perovskites and expect that the composite approach will be applicable to other classes of layered materials.
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