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The frequency response of the photocurrent (Iph) generated in perovskite photodetectors is a crucial issue in imaging or telecommunication applications, although it is briefly discussed in the literature. The present work obtains for the first time the complete expression of the Iph generated on MAPbI3 (MA:methylamoniumI) perovskite polycrystalline thin films. A conditioning circuit is used to extract Iph at 1 V of bias voltage under a square‐modulated laser excitation with a sensitivity smaller than 1 nW and a linear dynamic range LDR > 200 dB; It allows an accurate determination of the module of Iph together with the phase, which is not usually reported in photodetector systems. The frequency domain analysis reveals that Iph can be modeled by two fractional poles located at low (10 kHz) and high (39–250 kHz) cut‐off frequencies. Optimum geometrical parameters and excitation fluence are found for the wider response, resulting for the best device on a cut off frequency up to 250 kHz, and the reproduction of square‐modulated optical waves up to 100 kHz. These results represent an important strategy toward the electrical analysis of MAPbI3 (or other perovskite materials) for the design of posterior electronic stages, optimization of devices and determination of their figures of merit. [ABSTRACT FROM AUTHOR]

In this work, the kinetics of phase separation in ultrathin non-stoichiometric Si oxide (SiOx, x < 2) films during high-temperature annealing is studied by Monte Carlo simulations on a two-dimensional lattice. The separation of Si and Si oxide phases by redistribution of oxygen atoms between the neighboring Si-OaSi4-a (0 = a = 4) complexes composing the SiOx microstructure is considered. The net direction of oxygen redistribution corresponds to the decrease of the penalty energy of the participating complexes, which is taken into account by applying the Metropolis algorithm. As a result, the dependence of the morphology of the Si nano-structures formed in the Si oxide matrix on the initial SiOx stoichiometry is obtained. Isolated Si nanoparticles with irregular shapes form at x = 1. A progressive increase of the excess Si content leads to the formation of noodle-like and branched Si particles, local Si networks and finally fully percolated Si structures at the percolation threshold x ~ 0.7. [ABSTRACT FROM AUTHOR]

A silicon nanocrystal (Si NC) white light-emitting (λ = ∼400–900 nm) thin film with a relatively low resistivity of 1.6 × 104 Ω m has been prepared as an active medium for electrically driven Si light sources. The average size of Si NC is 2.4 ± 0.4 nm. To enhance the light emission efficiency of this low-resistivity Si NC thin film, approach of hydrogen passivation suitable for the traditional high-resistivity (1.2 × 107 Ω m in this work for example) red light-emitting Si NC thin film has been tried and found unavailable unfortunately. Our first principles simulation shows that Si NCs bonded to −O, −NH2, −OH, and −H ligands are responsible for red, green, and blue (RGB) primary color emissions in this white light-emitting sample, respectively. Passivation of the sample in NH3 and H2O atmosphere is then conducted, aiming to increase the number of the RGB light emitters. The light emission is significantly enhanced, with photoluminescence intensity, photoluminescence quantum yield, electroluminescence intensity, and net optical gains increased by factors of 4.6, 4.2, 4.0, and ∼3.0, respectively, after 10-day passivation. Further enhancements are expected for longer passivation. [ABSTRACT FROM AUTHOR]

Halide perovskites, in the form of thin films and colloidal nanocrystals, have recently taken semiconductor optoelectronics research by storm, and have emerged as promising candidates for high‐performance solar cells, light‐emitting diodes (LEDs), lasers, photodetectors, and radiation detectors. The impressive optical and optoelectronic properties, along with the rapid increase in efficiencies of solar cells and LEDs, have greatly attracted researchers across many disciplines. However, most advances made so far in terms of preparation (colloidal nanocrystals and thin films), and the devices with highest efficiencies are based on Pb‐based halide perovskites, which have raised concerns over their commercialization due to the toxicity of Pb. This has triggered the search for lower‐toxicity Pb‐free halide perovskites and has led to significant progress in the last few years. In this roadmap review, researchers of different expertise have joined together to summarize the latest progress, outstanding challenges, and future directions of Pb‐free halide perovskite thin films and nanocrystals, regarding their synthesis, optical spectroscopy, and optoelectronic devices, to guide the researchers currently working in this area as well as those that will join the field in the future. [ABSTRACT FROM AUTHOR]

Photocurrent matching in conventional monolithic tandem solar cells is achieved by choosing semiconductors with complementary absorption spectra and by carefully adjusting the optical properties of the complete top and bottom stacks. However, for thin film photovoltaic technologies at the module level, another design variable significantly alleviates the task of photocurrent matching, namely the cell width, whose modification can be readily realized by the adjustment of the module layout. Herein, this concept is demonstrated at the experimental level for the first time for a 2T‐mechanically stacked perovskite (FAPbBr3)/organic (PM6:Y6:PCBM) tandem mini‐module, an unprecedented approach for these emergent photovoltaic technologies fabricated in an independent manner. An excellent Isc matching is achieved by tuning the cell widths of the perovskite and organic modules to 7.22 mm (PCEPVKT‐mod = 6.69%) and 3.19 mm (PCEOPV‐mod = 12.46%), respectively, leading to a champion efficiency of 14.94% for the tandem module interconnected in series with an aperture area of 20.25 cm2. Rather than demonstrating high efficiencies at the level of small lab cells, this successful experimental proof‐of‐concept at the module level proves to be particularly useful to couple devices with non‐complementary semiconductors, either in series or in parallel electrical connection, hence overcoming the limitations imposed by the monolithic structure. [ABSTRACT FROM AUTHOR]

In spectroscopic ellipsometry, the optical properties of materials are obtained indirectly by generally assuming dielectric function and optical models. This ellipsometry analysis, which typically requires numerous model parameters, has essentially been performed by a trial-and-error approach, making this method as a rather time-consuming characterization technique. Here, we propose a fully automated spectroscopic ellipsometry analysis method, which can be applied to obtain dielectric functions of light absorbing materials in a full measured energy range without any prior knowledge of model parameters. The developed method consists of a multiple-step grid search and the following non-linear regression analysis. Specifically, in our approach, the analyzed spectral region is gradually expanded toward a higher energy, while incorporating an additional optical transition peak whenever the root mean square error of the fitting analysis exceeds a critical value. In particular, we have established a unique algorithm that could be employed for the ellipsometry analyses of different types of optical materials. The proposed scheme has been applied successfully for the analyses of MoOx transparent oxides and the complex dielectric function of a MoOx layer that exhibits dual optical transitions due to band-edge and deep-level absorptions has been determined. The developed method can drastically reduce a time necessary for an ellipsometry analysis, eliminating a serious drawback of a traditional spectroscopic ellipsometry analysis method. [ABSTRACT FROM AUTHOR]

Owing to the bandgap‐bowing effect, mixed lead‐tin halide perovskites provide ideal bandgaps for the bottom subcell of all‐perovskite tandem photovoltaic devices that offer fundamentally elevated power‐conversion efficiencies. However, these materials suffer from degradation in ambient air, which worsens their optoelectronic properties and hinders their usability for photovoltaic applications. Such degradation pathways are not yet fully understood, especially for the perovskites in the middle of the APbxSn1‐xI3 solid solution line, which offer the narrowest bandgaps across the range. This study unravels the degradation mechanisms of APbxSn1‐xI3 perovskites, reporting clear differences between mixed lead‐tin (x = 0.5) and tin‐only (x = 0) perovskites. The dynamic optoelectronic properties, electronic structure, crystal structure, and decomposition products of the perovskite thin films are examined in situ during air exposure. Both perovskite compositions suffer from the formation of defects over the timescale of hours, as indicated by a significant reduction in their charge‐carrier diffusion lengths. For tin‐only perovskite, degradation predominantly causes the formation of energetically shallow tin vacancies and hole doping. However, for mixed lead‐tin perovskite, deep trap states are formed that significantly accelerate charge‐carrier recombination, yet leave mobilities relatively unaffected. These findings highlight the need for passivation strategies tailored specifically to mixed lead‐tin iodide perovskites. [ABSTRACT FROM AUTHOR]

Transition metal oxides (TMOs) are of increasing importance for many applications reaching from thin-film transistors and non-volatile memory to novel contact layers in photovoltaics. Due to their tunable electrical properties and high transparency, TMOs are also promising candidates as contact layers in silicon heterojunction solar cells already leading to cell efficiencies of about 22%. However, the current extraction of charge carriers via these thin contact layers is still not fully understood. To assist the engineering of novel silicon heterojunctions, numerical device simulations are used to improve knowledge regarding relevant heterojunction and thin film properties. The efficient current extraction from a silicon absorber is investigated with Sentaurus TCAD for a TMO-based hole contact. It is shown that for an ideal hole extraction from the induced crystalline silicon pn-junction via the amorphous silicon buffer and the TMO into the external metal electrode, two requirements have to be fulfilled: (A) A sufficiently high TMO work function is needed to ensure a high hole conductivity (via a high charge carrier ratio p/n) in the induced pn-junction within the silicon absorber. (B) Extraction of those holes into the TMO calls for efficient trap-assisted tunneling. Experimental evidence for a limitation of hole extraction by (A) and (B) is given for a variety of TMO based hole contacts using molybdenum oxide. [ABSTRACT FROM AUTHOR]

Homogeneous films from SiO1.3 (250 nm thick) were deposited on crystalline Si substrates by thermal evaporation of silicon monoxide. A part of the films was further annealed at 700 °C to grow amorphous Si (a-Si) nanoclusters in an oxide matrix, thus producing composite a-Si-SiO1.8 films. Homogeneous as well as composite films were irradiated by 20-MeV electrons at fluences of 7.2 × 1014 and 1.44 × 1015 el/cm2. The film thicknesses and optical constants were explored by spectroscopic ellipsometry. The development of the phase composition of the films caused by the electron-beam irradiation was studied by transmission electron microscopy. The ellipsometric and electron microscopy results have shown that the SiOx films are optically homogeneous and the electron irradiation with a fluence of 7.2 × 1014 el/cm2 has led to small changes in the optical constants and the formation of very small a-Si nanoclusters. The irradiation of the a-Si-SiOx composite films caused a decrease in the effective refractive index and, at the same time, an increase in the refractive index of the oxide matrix. Irradiation induced increase in the optical band gap and decrease in the absorption coefficient of the thermally grown amorphous Si nanoclusters have also been observed. The obtained results are discussed in terms of the formation of small amorphous silicon nanoclusters in the homogeneous layers and electron irradiation induced reduction in the nanocluster size in the composite films. The conclusion for the nanoparticle size reduction is supported by infrared transmittance results. [ABSTRACT FROM AUTHOR]

Single‐component emitters with stable and bright warm white‐light emission are highly desirable for high‐efficacy warm white light‐emitting diodes (warm‐WLEDs), however, materials with such luminescence properties are extremely rare. Low-dimensional lead (Pb) halide perovskites can achieve warm white photoluminescence (PL), yet they suffer from low stability and PL quantum yield (PLQY). While Pb‐free air‐stable perovskites such as Cs2AgInCl6 emit desirable warm white light, sophisticated doping strategies are typically required to increase their PL intensity. Moreover, the use of rare metal‐bearing compounds along with the typically required vacuum‐based thin‐film processing may greatly increase their production cost. Herein, organic–inorganic hybrid cuprous (Cu+)‐based metal halide MA2CuCl3 (MA = CH3NH3+) that meets the requirements of i) nontoxicity, ii) high PLQY, and iii) dopant‐free is presented. Both single crystals and thin films of MA2CuCl3 can be facilely prepared by a low‐cost solution method, which demonstrate bright warm white‐light emission with intrinsically high PLQYs of 90–97%. Prototype electroluminescence devices and down‐conversion LEDs are fabricated with MA2CuCl3 thin films and single crystals, respectively, which show bright luminescence with decent efficiencies and operational stability. These findings suggest that MA2CuCl3 has a great potential for the single‐component indoor lighting and display applications. [ABSTRACT FROM AUTHOR]

Surface passivating thin films are crucial for limiting the electrical losses during charge carrier collection in silicon photovoltaic devices. Certain dielectric coatings of more than 10 nm provide excellent surface passivation, and ultra‐thin (<2 nm) dielectric layers can serve as interlayers in passivating contacts. Here, ultra‐thin passivating films of SiO2, Al2O3, and HfO2 are created via plasma‐enhanced atomic layer deposition and annealing. It is found that thin negatively charged HfO2 layers exhibit excellent passivation properties—exceeding those of SiO2 and Al2O3—with 0.9 nm HfO2 annealed at 450 °C providing a surface recombination velocity of 18.6 cm s−1. The passivation quality is dependent on annealing temperature and layer thickness, and optimum passivation is achieved with HfO2 layers annealed at 450 °C measured to be 2.2–3.3 nm thick which give surface recombination velocities ≤2.5 cm s−1 and J0 values of ≈14 fA cm−2. The superior passivation quality of HfO2 nanolayers makes them a promising candidate for future passivating contacts in high‐efficiency silicon solar cells. [ABSTRACT FROM AUTHOR]

2D hybrid perovskites are attractive for optoelectronic devices. In thin films, the color of optical emission and the texture of crystalline domains are often difficult to control. Here, a method for extinguishing or enhancing different emission features is demonstrated for the family of 2D Ruddlesden–Popper perovskites (EA1−xFAx)4Pb3Br10 (EA = ethylammonium, FA = formamidinium). When grown from aqueous hydrobromic acid, crystals of (EA1−xFAx)4Pb3Br10 retain all the emission features of their parent compound, (EA)4Pb3Br10. Surprisingly, when grown from dimethylformamide (DMF), an emission feature, likely self‐trapped exciton (STE), near 2.7 eV is missing. Extinction of this feature is correlated with DMF being incorporated between the 2D Pb‐Br sheets, forming (EA1−xFAx)4Pb3Br10∙(DMF)y. Without FA, films grown from DMF form (EA)4Pb3Br10, retain little solvent, and have strong emission near 2.7 eV. Slowing the kinetics of film growth strengthens a different emission feature, likely a different type of STE, which is much broader and present in all compositions. Films of (EA1−xFAx)4Pb3Br10∙(DMF)y have large, micron‐sized domains and homogeneous orientation of the semiconducting sheets, resulting in low electronic disorder near the absorption edge. The ability to selectively strengthen or extinguish different emission features in films of (EA1−xFAx)4Pb3Br10∙(DMF)y reveals a pathway to tune the emission color in these compounds. [ABSTRACT FROM AUTHOR]

Combining electron‐ and hole‐selective materials in one crystalline silicon (Si) solar cell, thereby avoiding any dopants, is not considered for application to photovoltaic industry until only comparable efficiency and stable performance are achievable. Here, it is demonstrated how a conventionally unstable electron‐selective contact (ESC) is optimized with huge boost in stability as well as improved electron transport. With the introduction of a Ti thin film between a‐Si:H(i)/LiF and Al electrode, high‐level passivation (Seff = 4.6 cm s–1) from a‐Si:H(i) and preferential band alignment (ρC = 7.9 mΩ cm2) from low work function stack of LiF/Ti/Al are both stably retained in the newly constructed n‐Si/a‐Si:H(i)/LiF/Ti/Al ESC. A detailed interfacial elements analysis reveals that the efficiently blocked inward diffusion of Al from electrode by the Ti protecting layer balances transport and recombination losses in general. This excellent electron‐selective properties in combination with large process tolerance that enable remarkable device performance, particularly high efficiencies of 22.12% and 23.61%, respectively, are successfully approached by heterojunction solar cells with dopant‐free ESC and dopant‐free contacts for both polarities. [ABSTRACT FROM AUTHOR]

In this work, high‐quality FASnI3 (FA, formamidinium) lead‐free perovskite thin films are successfully incorporated in a flexible polyethylene terephthalate (PET) substrate to demonstrate amplified spontaneous emission (ASE) and lasing. The waveguide (WG) consists of polymethylmethacrylate(PMMA)/FASnI3 bilayer deposited on a PET substrate and is properly designed to allow single‐mode propagation at the photoluminescence wavelength. This geometry optimizes the excitation of the emitting FASnI3, enhances the light−matter interaction in the semiconductor thin film, provides a preferable direction for the emitted light and allows its direct outcoupling for on‐chip or fiber‐optic applications. As far as the authors know, ASE and random lasing are obtained for the first time in a flexible‐based WG integrating a highly efficient lead‐free perovskite. The high quality of the deposited films and the optimized design of the structure result in an extremely low ASE/lasing threshold in the range of 1 µJ cm−2, which is only ten times higher than that measured in the same PMMA/FASnI3 structure deposited on a rigid substrate (Si/SiO2). More interestingly, these WGs exhibit a strong polarization anisotropy for the outcoupled ASE/lasing light with a preferable transverse electric polarization. This work is the base for the future development of ecofriendly, flexible, and efficient photonic devices. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the nonlinear optical response and theoretical efficiency of CH3NH3PbI3−xClx thin films from the optical transmission and reflection measurements. The dispersion of the complex refractive index is evaluated using the Wemple–DiDomenico single oscillator model. The oscillator energy (E0) of CH3NH3PbI3−xClx follows by an empirical relationship with optical bandgap (Eg) as E0 ≈ 2.41 Eg for chemical dip coating, spray, and E0 ≈ 1.63 Eg for dipping deposited samples, respectively. The long wavelength refractive index, average oscillator wavelength, and oscillator strength are also determined using the Sellmeier oscillator equation. The estimated third-order nonlinear optical susceptibility is found to be the order of 10−12 esu. The incident photon and charge carrier interaction in CH3NH3PbI3−xClx is studied from the dielectric response of the samples. The charge carrier excitation is found higher at lower wavelength and experienced bulk excitation in volume while surface excitation on the surface region. The optical conductivity of CH3NH3PbI3−xClx is notably high, which leads to an increase in carrier transfer through the extrinsic halide perovskite material expedient for higher conversion efficiency. The highest theoretical efficiency of CH3NH3PbI3−xClx is estimated to be 17.4%, which is in excellent agreement with the experimental report. From photosensitivity study, it is confirmed that CH3NH3PbI3−xClx films are highly photosensitive. All these results comprehend that CH3NH3PbI3−xClx is a potential candidate for photonic applications. [ABSTRACT FROM AUTHOR]

Here we present a colloidal approach to synthesize bismuth chalcohalide nanocrystals (BiEX NCs, in which E=S, Se and X=Cl, Br, I). Our method yields orthorhombic elongated BiEX NCs, with BiSCl crystallizing in a previously unknown polymorph. The BiEX NCs display a composition‐dependent band gap spanning the visible spectral range and absorption coefficients exceeding 105 cm−1. The BiEX NCs show chemical stability at standard laboratory conditions and form colloidal inks in different solvents. These features enable the solution processing of the NCs into robust solid films yielding stable photoelectrochemical current densities under solar‐simulated irradiation. Overall, our versatile synthetic protocol may prove valuable in accessing colloidal metal chalcohalide nanomaterials at large and contributes to establish metal chalcohalides as a promising complement to metal chalcogenides and halides for applied nanotechnology. [ABSTRACT FROM AUTHOR]

The ZnSnO film is fabricated using sol–gel process, and the change of its morphological feature, structure and optical properties with increasing heat‐treatment temperature is studied. Scanning electron microscopy (SEM) images display that the ZnSnO films consist of two different layers of component. The surface layer is crystalline zinc oxide (ZnO), and the bottom layer is amorphous ZnxSnyOz ternary compound. When the ZnSnO film carries out a heat‐treatment at 350 and 400 °C, the thickness and grain morphology of the ZnO layer are hardly changed. However, some pyramid‐shaped grains appear on the film surface, when the temperature rises to 450 °C. These ZnSnO films exhibit interesting optical properties: they all have the luminescence features of ZnO and the bandgap width similar to tin oxide (SnO2). The changes in the size and shape of the ZnO grains in the surface layer lead to obvious changes in the optical properties: the ultraviolet emission of the ZnSnO films is greatly enhanced, and the transmittance is gradually increased. The ZnSnO film with a special structure, namely, a double‐layer including a highly crystalline ZnO layer and amorphous ZnxSnyOz layer, has potential applications in optoelectronic devices. [ABSTRACT FROM AUTHOR]

The electron transport layer (ETL) is critical in perovskite solar cells (PSCs) as it controls the optics of the complete solar cell. This study uses an industrially viable RF magnetron sputtering technique to prepare the tungsten oxide (WOx) ETL for PSCs. Necessary morphological and optoelectronic investigations were carried out to ensure the high-quality WOx thin-film. The influence of the deposition power on the ETL thickness and PSC optics were systematically investigated. A three-dimensional (3D) finite-difference time-domain (FDTD) approach analyses the optics and optimization of the complete solar cell. The investigations allow the optimized planar PSC to determine the JSC of > 21 mA/cm2. The optical performance of the planar device is limited due to higher optical losses; hence, the current study proposes a PSC design embedded with Ag nanoparticles. The proposed PSC can improve the JSC by ~ 17% (up to 24.5 mA/cm2) than the planar device owing to improved light trapping, further boosting the PSC's energy conversion efficiency (ECE). A detailed discussion on film realization and solar cell optics is provided. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate a vacuum‐based evaporation approach to fabricate organic‐inorganic perovskite thin films by using phase‐formed halide perovskite nanoparticles (NPs) as a precursor/source. We are able to consistently obtain MAPbX3 (MA=CH3NH3 and X=Cl, Br or I) thin films at various substrates (e. g. glass, ITO, or plastic). The perovskite phase formation in thin film form is confirmed by x‐ray diffraction (XRD) studies. Small micro‐strain (tensile) values of 1.64×10−3, 1.42×10−3 and 6.85×10−4 obtained for MAPbCl3, MAPbBr3 and MAPbI3 films respectively from Williamson‐Hall equation indicate low structural distortions in perovskite thin films. The absorption spectra of thin films show sharp band edge having direct band gap, which is followed by narrow full width at half maxima (FWHM ∼0.1 eV) of the emission peak. Thin films of MAPbCl3, MAPbBr3 and MAPbI3 show direct band gap of 3.1 eV, 2.4 eV and 1.6 eV, respectively. Small Urbach energy values of 33 meV, 44 meV and 66 meV for MAPbCl3, MAPbBr3 and MAPbI3 films respectively indicates low defect density in various perovskite films. Scanning electron microscopy (SEM) along with energy‐dispersive X‐ray spectroscopy (EDS) shows high surface coverage and uniform chemical composition of MAPbX3 (X=Cl, Br and I) thin films deposited by the present method. We have successfully controlled the film thickness from 250 nm to 1 μm by varying the nanoparticle precursor amount. The perovskite thin films deposited by the present method are highly stable against the degradation under ambient conditions. Systematic XRD studies along with absorption data demonstrate that the MAPbCl3 and MAPbBr3 films stored under ambient conditions remained stable for more than 30 days and MAPbI3 films for more than 7 days. [ABSTRACT FROM AUTHOR]

Wide‐bandgap perovskites based on alloying cesium and formamidinium lead mixed halides (CsxFA1–xPb(IyBr1–y)3) have received great attention due to their potential application in high‐efficiency tandem solar cells. However, the fast crystallization of CsxFA1–xPb(IyBr1–y)3 perovskite films results in a high trap density and hinders the further enhancement of the photovoltaic performance. Herein, an intermediate engineering is developed to retard the fast crystallization of Cs0.17FA0.83PbI1.8Br1.2 wide‐bandgap perovskite by adding FACl in the precursor solution. The introduction of the FACl additive leads to the formation of a thermodynamic phase‐pure intermediate which facilitates the further crystallization of a high‐quality perovskite thin film at elevated temperature and thus enhances the ultimate device performance. The champion device achieves an efficiency over 19% and exhibits 83.8% retention after 50 days aging without encapsulation. [ABSTRACT FROM AUTHOR]

The making of BaZrS3 thin films by molecular beam epitaxy (MBE) is demonstrated. BaZrS3 forms in the orthorhombic distorted‐perovskite structure with corner‐sharing ZrS6 octahedra. The single‐step MBE process results in films smooth on the atomic scale, with near‐perfect BaZrS3 stoichiometry and an atomically sharp interface with the LaAlO3 substrate. The films grow epitaxially via two competing growth modes: buffered epitaxy, with a self‐assembled interface layer that relieves the epitaxial strain, and direct epitaxy, with rotated‐cube‐on‐cube growth that accommodates the large lattice constant mismatch between the oxide and the sulfide perovskites. This work sets the stage for developing chalcogenide perovskites as a family of semiconductor alloys with properties that can be tuned with strain and composition in high‐quality epitaxial thin films, as has been long‐established for other systems including Si‐Ge, III‐Vs, and II‐VIs. The methods demonstrated here also represent a revival of gas‐source chalcogenide MBE. [ABSTRACT FROM AUTHOR]

The hybrid organic–inorganic perovskite (HOIP) becomes a promising candidate for ultra-thin photoelectric batteries and skin-like sensors. However, homogeneous thin films of the material usually provide low absorption efficiency. In this work, by engineering the nanohole arrays on a HOIP ultrathin film, we successfully design an all-dielectric HOIP metasurface with broadband optical absorption enhancement through the finite-difference time-domain technique. The absorption enhancement arises from the Mie resonance, which can be tuned by varying the geometrical parameters and the spatial periodicity of the nanoholes. Compared with a uniform HOIP film, the HOIP metasurface significantly enhances the absorption over the entire visible regime, and the maximum absorption rate reaches 90%. Moreover, our design with multiple nanohole sizes provides consistently high absorption efficiency up to 51%–87% in a broad wavelength range of 400 nm–770 nm. Furthermore, the external quantum efficiency of a solar cell with our HOIP metasurface is 44% higher than that of a uniform HOIP film by assuming the ideal process with infinite carrier lifetime and negligible recombination. Our findings may provide a route for effective light trapping and efficient photoelectric conversion with ultrathin HOIP metasurfaces. [ABSTRACT FROM AUTHOR]

The anomalous optoelectronic properties of a quasi‐vertical orientated Chalcostibite CuSbS2 thin film synthesized on glass substrate are studied in detail. Two well‐separated absorption edges of CuSbS2 are identified by photothermal‐deflection spectroscopy (PDS) at 1.48 and 0.90 eV. The formation mechanism of the 0.9 eV infrared edge is found to be crystal orientation related. The properties of the 0.9 eV absorption edge are subject to detailed investigation using temperature‐dependent photoluminescence (TDPL) characterization, which attribute the origin of this phenomenon to a deep‐level defect state near the mid‐bandgap of CuSbS2. [ABSTRACT FROM AUTHOR]

Nitrogen doped hydrogenated amorphous silicon thin films, also recorded as silicon rich hydrogenated amorphous silicon nitride thin films, were deposited by plasma enhanced chemical vapor deposition. The structural evolution and mechanical properties of the films with different nitrogen contents were studied by Fourier transform infrared spectroscopy, Raman scattering spectroscopy, and the density and stress measurement system, respectively. The results showed that with the increase in ammonia gas flow rate from 0.5 SCCM to 20 SCCM, the tensile stress and the density of the films decreased from 600 MPa to 280 MPa and from 2.31 g/cm3 to 2.08 g/cm3, respectively. The hydrogen bonding configurations, hydrogen content, and structural ordering evolution were investigated to reveal the relationship between the structural and mechanical properties of the films. A qualitative model was proposed to explain the role of nitrogen and hydrogen atoms during the film growth. [ABSTRACT FROM AUTHOR]

The presence of a nonoptically active polymorph (yellow‐phase) competing with the optically active polymorph (black γ‐phase) at room temperature in cesium tin iodide (CsSnI3) and the susceptibility of Sn to oxidation represent two of the biggest obstacles for the exploitation of CsSnI3 in optoelectronic devices. Here room‐temperature single‐source in vacuum deposition of smooth black γ −CsSnI3 thin films is reported. This is done by fabricating a solid target by completely solvent‐free mixing of CsI and SnI2 powders and isostatic pressing. By controlled laser ablation of the solid target on an arbitrary substrate at room temperature, the formation of CsSnI3 thin films with optimal optical properties is demonstrated. The films present a bandgap of 1.32 eV, a sharp absorption edge, and near‐infrared photoluminescence emission. These properties and X‐ray diffraction of the thin films confirm the formation of the orthorhombic (B‐γ) perovskite phase. The thermal stability of the phase is ensured by applying in situ an Al2O3 capping layer. This work demonstrates the potential of pulsed laser deposition as a volatility‐insensitive single‐source growth technique of halide perovskites and represents a critical step forward in the development and future scalability of inorganic lead‐free halide perovskites. [ABSTRACT FROM AUTHOR]

Air‐stable inorganic cesium lead iodide (CsPbI3) perovskite thin films with a bandgap of 1.7 eV are a promising candidate for tandem cell solar cells, comprising a perovskite top cell with a crystalline silicon bottom cell. The device design and simulations are important to develop high‐efficiency photovoltaic devices. However, knowledge of complex optical constants of the CsPbI3 thin films is mandatory to complement such tasks. Herein, air‐stable inorganic CsPbI3 perovskite thin films are prepared using one‐step synthesis through a spin‐coating method. Variable angle spectroscopic ellipsometry (VASE) is then conducted at five angles (43.9°, 48.9°, 53.9°, 58.9°, and 63.9°) to obtain ellipsometric data (Ψ and Δ). The thickness nonuniformity model of the perovskite thin film combined with an effective medium approximation for describing rough surface is adopted to achieve excellent fitting. The complex optical constants of the CsPbI3 thin film are experimentally obtained in the wavelength range of 300–1200 nm. The present results open the door for design and simulations on high‐efficiency CsPbI3/c‐Si tandem solar cells. [ABSTRACT FROM AUTHOR]

We present some advanced characterization techniques developed to investigate on the opto-electronic properties of thin film semiconductors and apply them to perovskite layers. These techniques are the steady state photocarrier grating (SSPG) and the Fourier transform photocurrent spectroscopy (FTPS). The SSPG was developed to study the ambipolar diffusion length of carriers and the FTPS was imagined to measure the variations of the below gap absorption coefficient with the light energy, giving information on the defect densities of the gap responsible for this absorption. The potentialities of these techniques are first detailed and then exemplified by their application to thin film perovskites. To study their stability, these films were exposed to different environments, air or vacuum, and in their as-deposited state or after light-soaking with heavy light. We find that the diffusion length and density of states are quite stable, even after light-soaking, and suggest that the degradation of devices exposed to 1 sun mainly comes from the evolution of the contacts instead of the perovkite itself. [ABSTRACT FROM AUTHOR]

Perovskite materials show excellent photovoltaic performance along with simple processing and low‐energy requirements. Despite their high power conversion efficiency (PCE), instability in the presence of moisture is still a major challenge. An effective method to enhance perovskite stability is by reducing dimensionality through incorporation of long organic cations into the perovskite crystal, which improves charge‐carrier extraction efficiency of the perovskites compared to conventional 3D perovskites. Quasi‐2D perovskites or 2D/3D perovskites strike a good balance between PCE and stability, having much improved stability compared to 3D structures while retaining excellent optoelectronic properties. Yielding better thermal stability and broader absorption into the near‐infrared, formamidinium iodide (FAI) doping has positive influences yet tends to cause poor surface morphology. Here, we introduce highly stable MA/FA‐based quasi‐2D perovskite fabricated by mixed cation doping (MCD), which is repeated deposition of MA and FA cations onto a quasi‐2D perovskite layer. MCD enables better morphology and surface passivation, leading to fewer defects. MA/FA‐based quasi‐2D perovskite with quasi‐cubic structure has high humidity resistivity, remaining intact after 90 days under 60% relative humidity without encapsulation. The underlying mechanism is further explained by binding and formation energies of cation mixture in solution and perovskite structure through computational analysis. [ABSTRACT FROM AUTHOR]

The last five years have seen very active research in the field of environmentally friendly lead-free perovskite solar cells. Tin halide perovskites are certainly one of the most promising alternatives to lead-based perovskites, while the performance of present tin-based perovskite solar cells is still relatively low. Nevertheless, recent experiments on thin films with improved quality have indicated that tin halide perovskites can, in principle, provide a high device performance. In this Perspective, we summarize recent progress in the understanding of the fundamental photophysics of tin halide perovskite thin films. To identify the reason for the low performance of present devices, we discuss the energy loss mechanisms in solar cell structures from the viewpoint of photocarrier dynamics. [ABSTRACT FROM AUTHOR]

Hot-wire chemical vapor deposition (HWCVD) was utilized to develop a fast and high quality a-Si:H thin film fabrication method for poly-Si/SiOx carrier selective passivating contacts targeting at n-type passivated emitter rear totally diffused crystalline silicon solar cells. The microstructure and hydrogen content of the a-Si:H thin films were analyzed by Fourier-transform infrared spectroscopy in order to understand the influence of film properties on passivation and conductivity. Dense layers were found to be beneficial for good passivation. On the other hand, blistering appeared as a-Si:H layers became more and more dense. However, by adjusting the SiH4 flow rate and the substrate heater temperature, blistering of a-Si:H could be avoided. A suitable process window was found and firing-stable implied open circuit voltage (iVoc) of up to 738 mV was achieved. In addition to high iVoc, a low contact resistivity of 0.034 Ω cm2 was also achieved. The deposition rate of the a-Si:H layers was 7 Å/s by using HWCVD, which is one order of magnitude higher than the deposition rate reported using other deposition methods. [ABSTRACT FROM AUTHOR]

Metal Halide Perovskites (MHPs) have arisen as promising materials to construct cost-effective photovoltaic and light emission devices. The study of nonlinear optical properties of MHPs is necessary to get similar success in nonlinear photonic devices, which is practically absent in the literature. The determination of the third order nonlinear coefficients is typically done by the Z-scan technique, which is limited by the scattering of polycrystalline thin films. In this work, we have studied nonlinear optical properties of polycrystalline CH3NH3PbX3 (MAPbX3) thin films and colloidal CsPbX3 nanoparticles with three different bandgaps (X3 = I3, Br3, and Br1.5I1.5). Their bright generation of photoluminescence under infrared illumination demonstrates an excellent efficiency of multiphoton absorption. The nonlinear absorption coefficient (β) was studied by analyzing the transmitted light through the samples, observing the expected Eg−3 dependence with values as high as β = 1500 cm/GW. In addition, we proposed the use of a modified Z-scan technique with imaging processing to analyze the nonlinear refraction coefficient (n2) under the laser damage threshold. Our experimental data agree quite well with theoretical predictions, demonstrating the accuracy of the method and potential applications to other thin films. Moreover, n2 parameter reaches values of 3.5 cm2/GW, indicating the suitability of MHPs for nonlinear photonics. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) films were deposited by plasma enhanced atomic layer deposition (PE-ALD) system using tetrakis-dimethylamido-titanium (TDMAT) at 250 °C. We applied a new source feeding method, known as Discrete Feeding Method (DFM), to PE-ALD TiO2 process for comparing the deposition rate, the physical and electrical film properties with the films deposited by conventional ALD method. Various analytical studies were carried out to investigate the change of TiO2 thin film characteristics due to DFM application. As a result, the optimal process condition was obtained with high physical properties and productivity while keeping electrical characteristics equivalent to those of the conventional ALD condition. [ABSTRACT FROM AUTHOR]

We report on the microscopic structure of the SiOx layer and the transport mechanism in polycrystalline Si (poly-Si) passivated contacts, which enable high-efficiency crystalline Si (c-Si) solar cells. Using electron beam induced current (EBIC) measurements, we accurately map nanoscale conduction-enabling pinholes in 2.2 nm thick SiOx layers in a poly-Si/SiOx/c-Si stack. These conduction enabling pinholes appear as bright spots in EBIC maps due to carrier transport and collection limitations introduced by the insulating 2.2 nm SiOx layer. Performing high-resolution transmission electron microscopy at a bright spot identified with EBIC reveals that conduction pinholes in SiOx can be regions of thin tunneling SiOx rather than a geometric pinhole. Additionally, selectively etching the underlying poly-Si layer in contacts with 1.5 and 2.2 nm thick SiOx layers using tetramethylammonium hydroxide results in pinhole-like etch features in both contacts. However, EBIC measurements for a contact with a thinner, 1.5 nm SiOx layer do not reveal pinholes, which is consistent with uniform tunneling transport through the 1.5 nm SiOx layer. Finally, we theoretically show that reducing the metal to the c-Si contact size from microns, like in the p-type passivated emitter rear contact, to tens of nanometers, like in poly-Si contacts, allows lowering of the unpassivated contact area by several orders of magnitude, thus resulting in excellent passivation, as has been demonstrated for these contacts. [ABSTRACT FROM AUTHOR]

The power conversion efficiency of organic–inorganic hybrid perovskite solar cells has soared over the past ten years and currently rivals those of crystalline silicon and other thin‐film solar cells. Most of the research effort so far has been focused on three‐dimensional (3 D) perovskite crystals, producing devices with very high efficiency but poor operational and environmental stability. Two‐dimensional (2 D) Ruddlesden–Popper perovskite has recently shown its potential as a highly stable light absorber, albeit with low efficiency. This work reviews the current progress in attaining both high efficiency and stability in solar cells by using 2 D perovskite. In particular, the focus is on multidimensional perovskite as a way to combine the best characteristics of 3 D and 2 D perovskites. Future challenges and potential methods to boost the performance of multidimensional perovskite solar cells further are briefly presented. Simply the best: This work reviews current progress in attaining both high efficiency and stability in solar cells by using multidimensional perovskites, combining the best characteristics of 3 D and 2 D perovskites. Challenges and potential improvements of multidimensional perovskite solar cells are also presented. [ABSTRACT FROM AUTHOR]

Hybrid organic-inorganic perovskites have recently gained immense attention due to their unique optical and electronic properties and low production cost, which make them promising candidates for a wide range of optoelectronic devices. But unlike most other technologies, the breakthroughs witnessed in hybrid perovskite optoelectronics have outgrown the basic understanding of the fundamental material properties. For example, the effectiveness of charge transport in relation to film microstructure and processing has remained elusive. In this study, field-effect transistors are fabricated and evaluated in order to probe the nature and dynamics of charge transport in thin films of methylammonium lead iodide. A dramatic improvement is shown in the electrical properties upon solvent vapor annealing. The resulting devices exhibit ambipolar transport, with room-temperature hole and electron mobilities exceeding 10 cm2 V-1 s-1. The remarkable enhancement in charge carrier mobility is attributed to the increase in the grain size and passivation of grain boundaries via the formation of solvent complexes. [ABSTRACT FROM AUTHOR]

In devices with intrinsic amorphous silicon layer on a crystalline silicon substrate, the light absorbed in the amorphous layer can be weakly electronically coupled into the silicon base. Such carrier injection has previously been reported from measurements on finished devices containing stacks of intrinsic and doped amorphous silicon layers. Here, we use spectral response of photoluminescence, a contactless approach, to investigate this carrier injection on significantly simpler structures. In such devices, the effect of absorption in the front layer can be measured by the internal quantum efficiency. A highly absorbing front layer is expected to cause a drop in the quantum efficiency at short wavelengths. However, if electron‐hole pairs that are generated in the front layer are subsequently injected into the base, the optical losses will be reduced, resulting in a partial recovery of the quantum efficiency at short wavelengths. Here, we quantify the efficiency of carrier injection from the intrinsic amorphous silicon front layer to the crystalline silicon base, by measuring the spectral response of photoluminescence heterojunction test structures. For devices with just an intrinsic amorphous silicon layer, the carrier injection from the layer was found to be close to unity. In devices with intrinsic amorphous silicon layer on crystalline silicon substrate, the light absorbed in the amorphous layer can be weakly electronically coupled into the silicon base. Such carrier injection has previously been reported from measurements on finished devices containing stacks of intrinsic and doped amorphous silicon layers. Here, we use spectral response of photoluminescence, a contactless approach, to investigate this carrier injection on partially processed devices with no electric contacts. [ABSTRACT FROM AUTHOR]

The poly-Si carrier-selective passivating contacts (CSPCs) parasitically absorb a substantial amount of light, especially in the form of free carrier absorption. To minimize these losses, we developed CSPCs based on oxygen-alloyed poly-Si (poly-SiOx) and deployed them in c-Si solar cells. Transmission electron microscopy analysis indicates the presence of nanometer-scale silicon crystals within such poly-SiOx layers. By varying the O content during material deposition, we can manipulate the crystallinity of the poly-SiOx material and its absorption coefficient. Also, depending on the O content, the bandgap of the poly-SiOx material can be widened, making it transparent for longer wavelength light. Thus, we optimized the O alloying, doping, annealing, and hydrogenation conditions. As a result, an extremely high passivation quality for both n-type poly-SiOx (J0 = 3.0 fA/cm2 and iVoc = 740 mV) and p-type poly-SiOx (J0 = 17.0 fA/cm2 and iVoc = 700 mV) is obtained. A fill factor of 83.5% is measured in front/back-contacted solar cells with both polarities made up of poly-SiOx. This indicates that the carrier transport through the junction between poly-SiOx and c-Si is sufficiently efficient. To demonstrate the merit of poly-SiOx layers' high transparency at long wavelengths, they are deployed at the back side of interdigitated back-contacted (IBC) solar cells. A preliminary cell efficiency of 19.7% is obtained with much room for further improvement. Compared to an IBC solar cell with poly-Si CSPCs, a higher internal quantum efficiency at long wavelengths is observed for the IBC solar cell with poly-SiOx CSPCs, thus demonstrating the potential of poly-SiOx in enabling higher JSC. [ABSTRACT FROM AUTHOR]

GeSe is a promising absorber material for photovoltaic applications due to its attractive material, optical, and electrical properties as well as its low toxicity and earth abundance. The first GeSe-based solar cell with 1.48% efficiency has been recently reported through self-regulated rapid thermal sublimation. However, most of the fundamental physical and electronic properties of GeSe such as refractive index, dielectric constant, carrier mobility, lifetime, and diffusion length remain unclear, despite the necessity of this for the design of high-performance GeSe solar cells. In this work, the above basic properties of GeSe are systematically studied by using spectroscopic ellipsometry, space charge limited current measurements, and transient absorption spectroscopy. These comprehensive results provide a solid foundation for the further development of GeSe solar cells. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of microstructure on the degradation rate of methylammonium lead triiodide (MAPbI3) perovskite films upon exposure to light and oxygen. By comparing the oxygen induced degradation of perovskite films of different microstructure-fabricated using either a lead acetate trihydrate precursor or a solvent engineering technique-it is demonstrated that films with larger and more uniform grains and better electronic quality show a significantly reduced degradation compared to films with smaller, more irregular grains. The effect of degradation on the optical, compositional, and microstructural properties of the perovskite layers is characterized and it is demonstrated that oxygen induced degradation is initiated at the layer surface and grain boundaries. It is found that under illumination, irreversible degradation can occur at oxygen levels as low as 1%, suggesting that degradation can commence already during the device fabrication stage. Finally, this work establishes that improved thin-film microstructure, with large uniform grains and a low density of defects, is a prerequisite for enhanced stability necessary in order to make MAPbI3 a promising long lived and low cost alternative for future photovoltaic applications. [ABSTRACT FROM AUTHOR]

One of the obstacles towards efficient radiative recombination in hybrid perovskites is a low exciton binding energy, typically in the orders of tens of meV. It has been shown that the use of electron-donor additives can lead to a substantial reduction of the non-radiative recombination in perovskite films. Herein, the approach using small molecules with semiconducting properties, which are candidates to be implemented in future optoelectronic devices, is presented. In particular, highly luminescent perovskite-organic semiconductor composite thin films have been developed, which can be processed from solution in a simple coating step. By tuning the relative concentration of methylammonium lead bromide (MAPbBr3) and 9,9spirobifluoren-2-yl-diphenyl-phosphine oxide (SPPO1), it is possible to achieve photoluminescent quantum yields (PLQYs) as high as 85 %. This is attributed to the dual functions of SPPO1 that limit the grain growth while passivating the perovskite surface. The electroluminescence of these materials was investigated by fabricating multilayer LEDs, where charge injection and transport was found to be severely hindered for the perovskite/SPPO1 material. This was alleviated by partially substituting SPPO1 with a hole-transporting material, 1,3-bis( N-carbazolyl)benzene (mCP), leading to bright electroluminescence. The potential of combining perovskite and organic semiconductors to prepare materials with improved properties opens new avenues for the preparation of simple lightemitting devices using perovskites as the emitter. [ABSTRACT FROM AUTHOR]

Here, we successfully used a pure layer of [SiW11O39]8− polyoxomethalate (POM) structure as a thin-film scaffold layer for CH3NH3PbI3-based perovskite solar cells (PSCs). A smooth nanoporous surface of POM causes outstanding improvement of the photocurrent density, external quantum efficiency (EQE), and overall efficiency of the PSCs compared to mesoporous TiO2 (mp-TiO2) as scaffold layer. Average power conversion efficiency (PCE) values of 15.5 % with the champion device showing 16.3 % could be achieved by using POM and a sequential deposition method with the perovskite layer. Furthermore, modified and defect-free POM/perovskite interface led to elimination of the anomalous hysteresis in the current-voltage curves. The open-circuit voltage decay study shows promising decrease of the electron recombination in the POM-based PSCs, which is also related to the modification of the POM/ perovskite interface and higher electron transport inside the POM layer. [ABSTRACT FROM AUTHOR]

The meteoric rise of perovskite single-junction solar cells has been accompanied by similar stunning developments in perovskite tandem solar cells. Debuting with efficiencies less than 14% in 2014, silicon-perovskite solar cells are now above 25% and will soon surpass record silicon single-junction efficiencies. Unconstrained by the Shockley-Quiesser single-junction limit, perovskite tandems suggest a real possibility of true third-generation thin-film photovoltaics; monolithic all-perovskite tandems have reached 18% efficiency and will likely pass perovskite single-junction efficiencies within the next 5 years. Inorganic-organic metal-halide perovskites are ideal candidates for inclusion in tandem solar cells due to their high radiative recombination efficiencies, excellent absorption, long-range charge-transport, and broad ability to tune the bandgap. In this progress report, the development of perovskite tandem cells is reviewed, with presentation of their key motivations and challenges. In detail, it presents an overview of recombination layer materials, bandgap-tuneability, transparent contact architectures, and perovskite compounds for use in tandems. Theoretical estimates of efficiency for future tandem and triple-junction perovskite cells are presented, outlining roadmaps for future focused research. [ABSTRACT FROM AUTHOR]

Grazing-incidence X-ray scattering (GIXS) methods have proven to be a valuable asset for investigating the morphology of thin films at different length scales. Consequently, GIXS has been applied to the fast-progressing field of organometal halide perovskites. This exciting class of materials has propelled research in the areas of cheap and sustainable photovoltaics, light emitting devices, and optoelectronics in general. Especially, perovskite solar cells (PSC) have seen a remarkable rise in power conversion efficiencies, crossing the 20% mark after only five years of research. This research news outlines GIXS studies focusing on the most challenging research topics in the perovskite field today: Current-voltage hysteresis, device reproducibility, and long-term stability of PSC are inherently linked to perovskite film morphology. On the other hand, film formation depends on the choice of precursors and processing parameters; understanding their interdependence opens possibilities to tailor film morphologies. Owing to their tunability and moisture resistance, 2D perovskites have recently attracted attention. Examples of GIXS studies with different measurement and data analysis techniques are presented, highlighting especially in-situ investigations on the many kinetic processes involved. Thus, an overview on the toolbox of GIXS techniques is linked to the specific needs of research into organometal halide perovskite optoelectronics. [ABSTRACT FROM AUTHOR]

Traps limit the photovoltaic efficiency and affect the charge transport of optoelectronic devices based on hybrid lead halide perovskites. Understanding the nature and energy scale of these trap states is therefore crucial for the development and optimization of solar cell and laser technology based on these materials. Here, the low-temperature photoluminescence of formamidinium lead triiodide (HC(NH2)2PbI3) is investigated. A power-law time dependence in the emission intensity and an additional low-energy emission peak that exhibits an anomalous relative Stokes shift are observed. Using a rate-equation model and a Monte Carlo simulation, it is revealed that both phenomena arise from an exponential trap-density tail with characteristic energy scale of ≈3 meV. Charge-carrier recombination from sites deep within the tail is found to cause emission with energy downshifted by up to several tens of meV. Hence, such phenomena may in part be responsible for open-circuit voltage losses commonly observed in these materials. In this high-quality hybrid perovskite, trap states thus predominantly comprise a continuum of energetic levels (associated with disorder) rather than discrete trap energy levels (associated, e.g., with elemental vacancies). Hybrid perovskites may therefore be viewed as classic semiconductors whose band-structure picture is moderated by a modest degree of energetic disorder. [ABSTRACT FROM AUTHOR]

Boron-doped SiC thin films were deposited on N-type Si(100) substrates at various deposition conditions by means of HWCVD technology using silane (SiH4), methane (CH4), hydrogen(H2), diborane (B2H6, 5vol.% in H2) and argon (Ar) gas as precursors. Elements concentration was determined by RBS and ERD method. Chemical compositions were analyzed by FTIR and Raman spectroscopy. Solar cell structure with top grid Al electrode was prepared to investigate the photovoltaic response and to gain insight about the quality of films and their suitability for photovoltaic applications. Comparison of open-circuit voltage (VOC), short-circuit current (Isc), fill factor (FF) and efficiency (Ef) was discussed. [ABSTRACT FROM AUTHOR]

Rubidium (Rb) is explored as an alternative cation to use in a novel multication method with the formamidinium/methylammonium/cesium (Cs) system to obtain 1.73 eV bangap perovskite cells with negligible hysteresis and steady state efficiency as high as 17.4%. The study shows the beneficial effect of Rb in improving the crystallinity and suppressing defect migration in the perovskite material. The light stability of the cells examined under continuous illumination of 12 h is improved upon the addition of Cs and Rb. After several cycles of 12 h light-dark, the cell retains 90% of its initial efficiency. In parallel, sputtered transparent conducting oxide thin films are developed to be used as both rear and front transparent contacts on quartz substrate with less than 5% parasitic absorption of near infrared wavelengths. Using these developments, semi-transparent perovskite cells are fabricated with steady state efficiency of up to 16.0% and excellent average transparency of ≈84% between 720 and 1100 nm. In a tandem configuration using a 23.9% silicon cell, 26.4% efficiency (10.4% from the silicon cell) in a mechanically stacked tandem configuration is demonstrated which is very close to the current record for a single junction silicon cell of 26.6%. [ABSTRACT FROM AUTHOR]

Hydrogenated amorphous Si films were prepared by a plasma-enhanced chemical vapor deposition technique. As-deposited samples were then thermally annealed at various temperatures to obtain nanocrystalline silicon films. The microstructures and carrier-transport characteristics were investigated during the transition process from amorphous to nanocrystalline phase. It was found that the Hall mobility was improved while the dark conductivity was increased by over two orders of magnitude after annealing. Temperature-dependent Hall measurements were performed in the temperature range from 310 to 575 K. Hall mobility first increases with rising temperature to 400 K and then decreases with further increasing temperature. The different temperature dependence of Hall mobility shows that the microscopic mechanisms governing charge transport are different for nanocrystalline Si films in different temperature regions. [ABSTRACT FROM AUTHOR]

Recently, innovative perovskite hybrid solar cells have attracted great interest in solar cell research fields, such as dye-sensitized solar cells, organic photovoltaics, thin-film solar cells, and silicon solar cells, because their device efficiencies are gradually approaching those of crystalline Si solar cells, and they can be fabricated by cheap low-temperature solution processes. Here, we review the recent progress of innovative perovskite hybrid solar cells. The introduction includes the general concerns about solar cells and why we need innovative solar cells. The second part explains the structure and the material properties of hybrid perovskite materials. We focus on why the hybrid perovskite materials can exhibit excellent solar cell properties, such as high open-circuit voltage. The third part introduces recent progress in innovative perovskite hybrid solar cells, in terms of device architecture and deposition methods for dense perovskite thin films with full surface coverage. The device architecture is important in attaining high power conversion efficiency; the device operating mechanism is dependent on the device structure; and the pinhole-free dense perovskite thin films with full surface coverage are crucial for achieving high efficiency. Finally, we summarize the recent progress in perovskite hybrid solar cells, and the issues to be solved, in the summary and outlook section. [ABSTRACT FROM AUTHOR]

Organic-inorganic perovskites are currently one of the hottest topics in photovoltaic (PV) research, with power conversion efficiencies (PCEs) of cells on a laboratory scale already competing with those of established thin-film PV technologies. Most enhancements have been achieved by improving the quality of the perovskite films, suggesting that the optimization of film formation and crystallization is of paramount importance for further advances. Here, we review the various techniques for film formation and the role of the solvents and precursors in the processes. We address the role chloride ions play in film formation of mixed-halide perovskites, which is an outstanding question in the field. We highlight the material properties that are essential for high-efficiency operation of solar cells, and identify how further improved morphologies might be achieved. [ABSTRACT FROM AUTHOR]