Highly efficient light management for perovskite solar cells

Organic-inorganic halide perovskite solar cells have enormous potential to impact the existing photovoltaic industry. As realizing a higher conversion efficiency of the solar cell is still the most crucial task, a great number of schemes were proposed to minimize the carrier loss by optimizing the electrical properties of the perovskite solar cells. Here, we focus on another significant aspect that is to minimize the light loss by optimizing the light management to gain a high efficiency for perovskite solar cells. In our scheme, the slotted and inverted prism structured SiO₂ layers are adopted to trap more light into the solar cells, and a better transparent conducting oxide layer is employed to reduce the parasitic absorption. For such an implementation, the efficiency and the serviceable angle of the perovskite solar cell can be promoted impressively. This proposal would shed new light on developing the high-performance perovskite solar cells.

Effective solvent-additive enhanced crystallization and coverage of absorber layers for high efficiency formamidinium perovskite solar cells

For a high efficiency of planar-type perovskite solar cells, a good crystallization and high surface coverage of the absorber films are required.

Solvent engineering for fast growth of centimetric high-quality CH3NH3PbI3 perovskite single crystals

Single crystals of size up to 1.7 centimeters are grown at 70 °C in a GBL/ACN binary solvent mixture.

Low electron-polar optical phonon scattering as a fundamental aspect of carrier mobility in methylammonium lead halide CH3NH3PbI3 perovskites

Calculated mobility of CH₃NH₃PbI₃ in two temperature regions, characterized by the dominance of electron-acoustic phonon scattering (left) and electron-polar optical phonon scattering (right).

High performance perovskite solar cell via multi-cycle low temperature processing of lead acetate precursor solutions

A lead acetate-based precursor, as a lead source in CH₃NH₃PbI₃ perovskite, showed potential in rapidly (<60 seconds) forming homogeneous films with a very smooth interface and large grain growth at relatively low temperatures via multi-step coating.

How photon pump fluence changes the charge carrier relaxation mechanism in an organic–inorganic hybrid lead triiodide perovskite

The fluence dependent charge carrier relaxation dynamics in a FAPbI₃ polycrystalline thin film were measured using femtosecond transient absorption and terahertz spectroscopies.

Enhancing the carrier thermalization time in organometallic perovskites by halide mixing

Non-adiabatic molecular dynamics simulations of non-radiative relaxation dynamics of charge carriers in hybrid perovskites show that the carrier relaxation time can be considerably increased by halide mixing.

Polyethylenimine as a dual functional additive for electron transporting layer in efficient solution processed planar heterojunction perovskite solar cells

The device performance is enhanced by doping a small percentage of polyethylenimine (PEI) into the PCBM.

Controlled growth of organic–inorganic hybrid CH3NH3PbI3 perovskite thin films from phase-controlled crystalline powders

High-performance MAPbI₃ perovskite solar cells with 16% efficiency are fabricated from phase-controlled crystalline powders.

Can ferroelectric polarization explain the high performance of hybrid halide perovskite solar cells?

Ferroelectricity can lead to creation of channels for efficient transport, however it is unlikely to explain the high open-circuit voltage (V_OC), typical of high performance perovskite solar cells.

Photoluminescence study of time- and spatial-dependent light induced trap de-activation in CH3NH3PbI3 perovskite films

Confocal photoluminescence microscopy is applied to investigate the time and spatial characteristics of light-induced trap de-activation in CH₃NH₃PbI₃ perovskite films.

A facile way to prepare nanoporous PbI2 films and their application in fast conversion to CH3NH3PbI3

Nanoporous PbI₂ films, prepared in a facile way, are applied to accelerate the reaction in the two-step deposition of CH₃NH₃PbI₃.

Rapid growth of high quality perovskite crystal by solvent mixing

The formation mechanism of perovskite crystal in different mixed solvents.

Photodynamic response of a solution-processed organolead halide photodetector

CH₃NH₃PbI₃ perovskite semiconductors have received intensive attention as a light absorbing material in high performance solar cells and photodetectors.

Anatase Mg0.05Ta0.95O1.15N0.85: a novel photocatalyst for solar hydrogen production

Anatase Mg_0.05Ta_0.95O_1.15N_0.85, exhibiting a narrow band gap for solar hydrogen, is a promising visible-light-response photocatalyst for photocatalytic or photoelectrochemical water splitting.

Organic–inorganic interactions of single crystalline organolead halide perovskites studied by Raman spectroscopy

Perovskite single crystals with varied cations and halides have been grown for Raman spectroscopic study of their organic–inorganic interactions.

Modulating carrier dynamics through perovskite film engineering

The one-sentence summary that highlights the novelty of our work is, “morphology-kinetics studies on substrate/film-treated perovskite samples reveal that the highly effective toluene-wash processes surprisingly increase trap density in CH₃NH₃PbI₃ films”.

Room-temperature fabrication of multi-deformable perovskite solar cells made in a three-dimensional gel framework

Ultraflexible perovskite solar cells are made by absorbing solar cell materials into 3D gel framework, yielding enhanced photovoltaic performances under deformations.

Recent progress on stability issues of organic–inorganic hybrid lead perovskite-based solar cells

Over the past few years, substantial progress has been made in research on organic–inorganic halide perovskite solar cells.

Electro-spray deposition of a mesoporous TiO2 charge collection layer: toward large scale and continuous production of high efficiency perovskite solar cells

The spin-coating method, which is widely used for thin film device fabrication, is incapable of large-area deposition or being performed continuously. In perovskite hybrid solar cells using CH(3)NH(3)PbI(3) (MAPbI(3)), large-area deposition is essential for their potential use in mass production. Prior to replacing all the spin-coating process for fabrication of perovskite solar cells, herein, a mesoporous TiO(2) electron-collection layer is fabricated by using the electro-spray deposition (ESD) system. Moreover, impedance spectroscopy and transient photocurrent and photovoltage measurements reveal that the electro-sprayed mesoscopic TiO(2) film facilitates charge collection from the perovskite. The series resistance of the perovskite solar cell is also reduced owing to the highly porous nature of, and the low density of point defects in, the film. An optimized power conversion efficiency of 15.11% is achieved under an illumination of 1 sun; this efficiency is higher than that (13.67%) of the perovskite solar cell with the conventional spin-coated TiO(2) films. Furthermore, the large-area coating capability of the ESD process is verified through the coating of uniform 10 × 10 cm(2) TiO(2) films. This study clearly shows that ESD constitutes therefore a viable alternative for the fabrication of high-throughput, large-area perovskite solar cells.

TiO2 quantum dots as superb compact block layers for high-performance CH3NH3PbI3 perovskite solar cells with an efficiency of 16.97

A compact TiO(2) layer is crucial to achieve high-efficiency perovskite solar cells. In this study, we developed a facile, low-cost and efficient method to fabricate a pinhole-free and ultrathin blocking layer based on highly crystallized TiO(2) quantum dots (QDs) with an average diameter of 3.6 nm. The surface morphology of the blocking layer and the photoelectric performance of the perovskite solar cells were investigated by spin-coating with three different materials: colloidal TiO(2) QDs, titanium precursor solution, and aqueous TiCl(4). Among these three treatments, the perovskite solar cell based on the TiO(2) QD compact layer offered the highest power conversion efficiency (PCE) of 16.97% with a photocurrent density of 22.48 mA cm(-2), a photovoltage of 1.063 V and a fill factor of 0.71. The enhancement of PCE mainly stems from the small series resistance and the large shunt resistance of the TiO(2) QD layer.

Charge-Carrier Dynamics and Mobilities in Formamidinium Lead Mixed-Halide Perovskites

The mixed-halide perovskite FAPb(Bry I1-y )3 is attractive for color-tunable and tandem solar cells. Bimolecular and Auger charge-carrier recombination rate constants strongly correlate with the Br content, y, suggesting a link with electronic structure. FAPbBr3 and FAPbI3 exhibit charge-carrier mobilities of 14 and 27 cm(2) V(-1) s(-1) and diffusion lengths exceeding 1 μm, while mobilities across the mixed Br/I system depend on crystalline phase disorder.

Superior Optical Properties of Perovskite Nanocrystals as Single Photon Emitters

The power conversion efficiency of photovoltaic devices based on semiconductor perovskites has reached ∼20% after just several years of research efforts. With concomitant discoveries of other promising applications in lasers, light-emitting diodes, and photodetectors, it is natural to anticipate what further excitement these exotic perovskites could bring about. Here we report on the observation of single photon emission from single CsPbBr3 perovskite nanocrystals (NCs) synthesized from a facile colloidal approach. Compared with traditional metal-chalcogenide NCs, these CsPbBr3 NCs exhibit nearly 2 orders of magnitude increase in their absorption cross sections at similar emission colors. Moreover, the radiative lifetime of CsPbBr3 NCs is greatly shortened at both room and cryogenic temperatures to favor an extremely fast output of single photons. The above superior optical properties have paved the way toward quantum-light applications of perovskite NCs in various quantum information processing schemes.

Air-Stable Surface-Passivated Perovskite Quantum Dots for Ultra-Robust, Single- and Two-Photon-Induced Amplified Spontaneous Emission

We demonstrate ultra-air- and photostable CsPbBr3 quantum dots (QDs) by using an inorganic-organic hybrid ion pair as the capping ligand. This passivation approach to perovskite QDs yields high photoluminescence quantum yield with unprecedented operational stability in ambient conditions (60 ± 5% lab humidity) and high pump fluences, thus overcoming one of the greatest challenges impeding the development of perovskite-based applications. Due to the robustness of passivated perovskite QDs, we were able to induce ultrastable amplified spontaneous emission (ASE) in solution processed QD films not only through one photon but also through two-photon absorption processes. The latter has not been observed before in the family of perovskite materials. More importantly, passivated perovskite QD films showed remarkable photostability under continuous pulsed laser excitation in ambient conditions for at least 34 h (corresponds to 1.2 × 10(8) laser shots), substantially exceeding the stability of other colloidal QD systems in which ASE has been observed.

Analysing the effect of crystal size and structure in highly efficient CH3NH3PbI3 perovskite solar cells by spatially resolved photo- and electroluminescence imaging

CH3NH3PbI3 perovskite solar cells with a mesoporous TiO2 layer and spiro-MeOTAD as a hole transport layer (HTL) with three different CH3NH3I concentrations (0.032 M, 0.044 M and 0.063 M) were investigated. Strong variations in crystal size and morphology resulting in diversified cell efficiencies (9.2%, 16.9% and 12.3%, respectively) were observed. The physical origin of this behaviour was analysed by detailed characterization combining current-voltage curves with photo- and electroluminescence (PL and EL) imaging as well as light beam induced current measurements (LBIC). It was found that the most efficient cell shows the highest luminescence and the least efficient cell is most strongly limited by non-radiative recombination. Crystal size, morphology and distribution in the capping layer and in the porous scaffold strongly affect the non-radiative recombination. Moreover, the very non-uniform crystal structure with multiple facets, as evidenced by SEM images of the 0.032 M device, suggests the creation of a large number of grain boundaries and crystal dislocations. These defects give rise to increased trap-assisted non-radiative recombination as is confirmed by high-resolution μ-PL images. The different imaging techniques used in this study prove to be well-suited to spatially investigate and thus correlate the crystal morphology of the perovskite layer with the electrical and radiative properties of the solar cells and thus with their performance.

Chloride Incorporation Process in CH₃NH₃PbI(3-x)Cl(x) Perovskites via Nanoscale Bandgap Maps

CH3NH3PbI(3-x)Cl(x) perovskites enable fabrication of highly efficient solar cells. Chloride ions benefit the morphology, carrier diffusion length, and stability of perovskite films; however, whether those benefits stem from the presence of Cl(-) in the precursor solution or from their incorporation in annealed films is debated. In this work, the photothermal-induced resonance, an in situ technique with nanoscale resolution, is leveraged to measure the bandgap of CH3NH3PbI(3-x)Cl(x) films obtained by a multicycle coating process that produces high efficiency (∼16%) solar cells. Because chloride ions modify the perovskite lattice, thereby widening the bandgap, measuring the bandgap locally yields the local chloride content. After a mild annealing (60 min, 60 °C) the films consist of Cl-rich (x < 0.3) and Cl-poor phases that upon further annealing (110 °C) evolve into a homogeneous Cl-poorer (x < 0.06) phase, suggesting that methylammonium-chrloride is progressively expelled from the film. Despite the small chloride content, CH3NH3PbI(3-x)Cl(x) films show better thermal stability up to 140 °C with respect CH3NH3PbI3 films fabricated with the same methodology.

Comparison of Recombination Dynamics in CH3NH3PbBr3 and CH3NH3PbI3 Perovskite Films: Influence of Exciton Binding Energy

Understanding carrier recombination in semiconductors is a critical component when developing practical applications. Here we measure and compare the monomolecular, bimolecular, and trimolecular (Auger) recombination rate constants of CH3NH3PbBr3 and CH3NH3PbI3. The monomolecular and bimolecular recombination rate constants for both samples are limited by trap-assisted recombination. The bimolecular recombination rate constant for CH3NH3PbBr3 is ∼3.3 times larger than that for CH3NH3PbI3 and both are in line with that found for radiative recombination in other direct-gap semiconductors. The Auger recombination rate constant is 4 times larger in lead-bromide-based perovskite compared with lead-iodide-based perovskite and does not follow the reduced Auger rate when the bandgap increases. The increased Auger recombination rate, which is enhanced by Coulomb interactions, can be ascribed to the larger exciton binding energy, ∼40 meV, in CH3NH3PbBr3 compared with ∼13 meV in CH3NH3PbI3.

Microstructures of Organometal Trihalide Perovskites for Solar Cells: Their Evolution from Solutions and Characterization

The use of organometal trihalide perovskites (OTPs) in perovskite solar cells (PSCs) is revolutionizing the field of photovoltaics, which is being led by advances in solution processing of OTP thin films. First, we look at fundamental phenomena pertaining to nucleation/growth, coarsening, and microstructural evolution involved in the solution-processing of OTP thin films for PSCs from a materials-science perspective. Established scientific principles that govern some of these phenomena are invoked in the context of specific literature examples of solution-processed OTP thin films. Second, the nature and the unique characteristics of OTP thin-film microstructures themselves are discussed from a materials-science perspective. Finally, we discuss the challenges and opportunities in the characterization of OTP thin films for not only gaining a deep understanding of defects and microstructures but also elucidating classical and nonclassical phenomena pertaining to nucleation/growth, coarsening, and microstructural evolution in these films. The overall goal is to have deterministic control over the solution-processing of tailored OTP thin films with desired morphologies and microstructures.

CH3NH3PbI3 perovskite single crystals: surface photophysics and their interaction with the environment

Here we identify structural inhomogeneity on a micrometer scale across the surface of a CH3NH3PbI3 perovskite single crystal. At the crystal edge a local distortion of the crystal lattice is responsible for a widening of the optical bandgap and faster photo-carrier recombination. These effects are inherently present at the edge of the crystal, and further enhanced upon water intercalation, as a preliminary step in the hydration of the perovskite material.

Enhanced optoelectronic quality of perovskite thin films with hypophosphorous acid for planar heterojunction solar cells

Solution-processed metal halide perovskite semiconductors, such as CH₃NH₃PbI₃, have exhibited remarkable performance in solar cells, despite having non-negligible density of defect states. A likely candidate is halide vacancies within the perovskite crystals, or the presence of metallic lead, both generated due to the imbalanced I/Pb stoichiometry which could evolve during crystallization. Herein, we show that the addition of hypophosphorous acid (HPA) in the precursor solution can significantly improve the film quality, both electronically and topologically, and enhance the photoluminescence intensity, which leads to more efficient and reproducible photovoltaic devices. We demonstrate that the HPA can reduce the oxidized I₂ back into I⁻, and our results indicate that this facilitates an improved stoichiometry in the perovskite crystal and a reduced density of metallic lead.

An imbalance in I/Pb stoichiometry is thought to lead to defects in metal halide films. Here, Zhang et al. show that the addition of hypophosphorous acid in the precursor solution can significantly improve the film quality and enhance the photoluminescence intensity, leading to improved photovoltaic devices.

Solar Electricity and Solar Fuels: Status and Perspectives in the Context of the Energy Transition

The energy transition from fossil fuels to renewables is already ongoing, but it will be a long and difficult process because the energy system is a gigantic and complex machine. Key renewable energy production data show the remarkable growth of solar electricity technologies and indicate that crystalline silicon photovoltaics (PV) and wind turbines are the workhorses of the first wave of renewable energy deployment on the TW scale around the globe. The other PV alternatives (e.g., copper/indium/gallium/selenide (CIGS) or CdTe), along with other less mature options, are critically analyzed. As far as fuels are concerned, the situation is significantly more complex because making chemicals with sunshine is far more complicated than generating electric current. The prime solar artificial fuel is molecular hydrogen, which is characterized by an excellent combination of chemical and physical properties. The routes to make it from solar energy (photoelectrochemical cells (PEC), dye-sensitized photoelectrochemical cells (DSPEC), PV electrolyzers) and then synthetic liquid fuels are presented, with discussion on economic aspects. The interconversion between electricity and hydrogen, two energy carriers directly produced by sunlight, will be a key tool to distribute renewable energies with the highest flexibility. The discussion takes into account two concepts that are often overlooked: the energy return on investment (EROI) and the limited availability of natural resources-particularly minerals-which are needed to manufacture energy converters and storage devices on a multi-TW scale.

High-Performance Planar-Type Photodetector on (100) Facet of MAPbI3 Single Crystal

Recently, the discovery of organometallic halide perovskites provides promising routes for fabricating optoelectronic devices with low cost and high performance. Previous experimental studies of MAPbI₃ optoelectronic devices, such as photodetectors and solar cells, are normally based on polycrystalline films. In this work, a high-performance planar-type photodetector fabricated on the (100) facet of a MAPbI₃ single crystal is proposed. We demonstrate that MAPbI₃ photodetector based on single crystal can perform much better than that on polycrystalline-film counterpart. The low trap density of MAPbI₃ single crystal accounts for the higher carrier mobility and longer carrier diffusion length, resulted in a significant performance increasement of MAPbI₃ photodetector. Compared with similar planar-type photodetectors based on MAPbI₃ polycrystalline film, our MAPbI₃ single crystal photodetector showed excellent performance with good stability and durability, broader response spectrum to near-infrared region, about 10² times higher responsivity and EQE, and approximately 10³ times faster response speed. These results may pave the way for exploiting high-performance perovskites photodetectors based on single crystal.

Planar-integrated single-crystalline perovskite photodetectors

Hybrid perovskites are promising semiconductors for optoelectronic applications. However, they suffer from morphological disorder that limits their optoelectronic properties and, ultimately, device performance. Recently, perovskite single crystals have been shown to overcome this problem and exhibit impressive improvements: low trap density, low intrinsic carrier concentration, high mobility, and long diffusion length that outperform perovskite-based thin films. These characteristics make the material ideal for realizing photodetection that is simultaneously fast and sensitive; unfortunately, these macroscopic single crystals cannot be grown on a planar substrate, curtailing their potential for optoelectronic integration. Here we produce large-area planar-integrated films made up of large perovskite single crystals. These crystalline films exhibit mobility and diffusion length comparable with those of single crystals. Using this technique, we produced a high-performance light detector showing high gain (above 10(4) electrons per photon) and high gain-bandwidth product (above 10(8) Hz) relative to other perovskite-based optical sensors.

Probing Photocurrent Generation, Charge Transport, and Recombination Mechanisms in Mesostructured Hybrid Perovskite through Photoconductivity Measurements

Conductivity of methylammonium lead triiodide (MAPbI3) perovskite was measured on different mesoporous metal oxide scaffolds: TiO2, Al2O3, and ZrO2, as a function of incident light irradiation and temperature. It was found that MAPbI3 exhibits intrinsic charge separation, and its conductivity stems from a majority of free charge carriers. The crystal morphology of the MAPbI3 was found to significantly affect the photoconductivity, whereas in the dark the conductivity is governed by the perovskite in the pores of the mesoporous scaffold. The temperature-dependent conductivity measurements also indicate the presence of states within the band gap of the perovskite. Despite a relatively large amount of crystal defects in the measured material, the main recombination mechanism of the photogenerated charges is bimolecular (band-to-band), which suggests that the defect states are rather inactive in the recombination. This may explain the remarkable efficiencies obtained for perovskite solar cells prepared with wet-chemical methods.

Transition from the Tetragonal to Cubic Phase of Organohalide Perovskite: The Role of Chlorine in Crystal Formation of CH3NH3PbI3 on TiO2 Substrates

The role of chlorine in the superior electronic property and photovoltaic performance of CH3NH3PbI(3-x)Clx perovskite has attracted recent research attention. Here, we study the impact of chlorine in the perspective of the crystal structure of the perovskite layer, which can provide important understanding of its excellent charge mobility and extended lifetimes. In particular, we find that in the presence of chlorine (PbCl2 or CH3NH3Cl), when CH3NH3PbI3 films are deposited on a TiO2 mesoporous layer instead of a planar TiO2 substrate, a stable cubic phase rather than the commonly observed tetragonal phase is formed in CH3NH3PbI3 perovskite at room temperature. The relative peak intensity of two major facets of cubic CH3NH3PbI3 crystals, (100)C and (200)C facets, can also be easily tuned, depending on the film thickness. Furthermore, compared with pristine CH3NH3PbI3 perovskite films, in the presence of chlorine, CH3NH3PbI3 crystals grown on planar substrates exhibit strong preferred orientations on (110)T and (220)T facets.

Stable and Efficient Perovskite Solar Cells Based on Titania Nanotube Arrays

Highly ordered 1D TiO2 nanotube arrays are fabricated and applied as nanocontainers and electron transporting material in CH3 NH3 PbI3 perovskite solar cells. The optimized device shows a power conversion efficiency of 14.8%, and improved stability under an illumination of 100 mW cm(-2). This is the best result based on 1D TiO2 nanostructures so far.

The Renaissance of Halide Perovskites and Their Evolution as Emerging Semiconductors

The recent re-emergence of the halide perovskites, of the type AMX3, derives from a sea-changing breakthrough in the field of photovoltaics that has led to a whole new generation of solar devices with remarkable power conversion efficiency. The success in the field of photovoltaics has led to intense, combined research efforts to better understand these materials both from the fundamental chemistry and physics points of view and for the improvement of applied functional device engineering. This groundswell of activity has breathed new life into this long-known but largely "forgotten" class of perovskites. The impressive achievements of halide perovskites in photovoltaics, as well as other optoelectronic applications, stem from an unusually favorable combination of optical and electronic properties, with the ability to be solution processed into films. This defines them as a brand new class of semiconductors that can rival or exceed the performance of the venerable classes of III-V and II-IV semiconductors, which presently dominate the industries of applied optoelectronics. Our aim in this Account is to highlight the basic pillars that define the chemistry of the halide perovskites and their unconventional electronic properties through the prism of structure-property relationships. We focus on the synthetic requirements under which a halide perovskite can exist and emphasize how the synthetic conditions can determine the structural integrity and the bulk properties of the perovskites. Then we proceed to discuss the origins of the optical and electronic phenomena, using the perovskite crystal structure as a guide. Some of the most remarkable features of the perovskites dealt with in this Account include the evolution of a unique type of defect, which gives rise to superlattices. These can enhance or diminish the fluorescence properties of the perovskites. For example, the exotic self-doping ability of the Sn-based perovskites allows them to adopt electrical properties from semiconducting to metallic. We attempt to rationalize how these properties can be tuned and partially controlled through targeted synthetic procedures for use in electronic and optical devices. In addition, we address open scientific questions that pose big obstacles in understanding the fundamentals of perovskites. We anticipate that the answers to these questions will provide the impetus upon which future research directions will be founded.