Two organolead halide perovskite nanocrystals, CH3NH3PbBr3 and CH3NH3PbI3, were found to efficiently sensitize TiO2 for visible-light conversion in photoelectrochemical cells. When self-assembled on mesoporous TiO2 films, the nanocrystalline perovskites exhibit strong band-gap absorptions as semiconductors. The CH3NH3PbI3-based photocell with spectral sensitivity of up to 800 nm yielded a solar energy conversion efficiency of 3.8%. The CH3NH3PbBr3-based cell showed a high photovoltage of 0.96 V with an external quantum conversion efficiency of 65%.

Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells

The energy costs associated with separating tightly bound excitons (photoinduced electron-hole pairs) and extracting free charges from highly disordered low-mobility networks represent fundamental losses for many low-cost photovoltaic technologies. We report a low-cost, solution-processable solar cell, based on a highly crystalline perovskite absorber with intense visible to near-infrared absorptivity, that has a power conversion efficiency of 10.9% in a single-junction device under simulated full sunlight. This "meso-superstructured solar cell" exhibits exceptionally few fundamental energy losses; it can generate open-circuit photovoltages of more than 1.1 volts, despite the relatively narrow absorber band gap of 1.55 electron volts. The functionality arises from the use of mesoporous alumina as an inert scaffold that structures the absorber and forces electrons to reside in and be transported through the perovskite.

https://science.sciencemag.org/content/sci/early/2012/10/03/science.1228604.full.pdf

Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites

Organic-inorganic perovskites have shown promise as high-performance absorbers in solar cells, first as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, we report transient absorption and photoluminescence-quenching measurements to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide (CH3NH3PbI(3-x)Cl(x)) and triiodide (CH3NH3PbI3) perovskite absorbers. We found that the diffusion lengths are greater than 1 micrometer in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. In contrast, the triiodide absorber has electron-hole diffusion lengths of ~100 nanometers. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a critical parameter to optimize for future perovskite absorber development.

/pdf/electron-hole-diffusion-lengths-exceeding-1-micrometer-in-an-3rhimkkmrj.pdf

Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber.

Access to clean, affordable and reliable energy has been a cornerstone of the world's increasing prosperity and economic growth since the beginning of the industrial revolution. Our use of energy in the twenty–first century must also be sustainable. Solar and water–based energy generation, and engineering of microbes to produce biofuels are a few examples of the alternatives. This Perspective puts these opportunities into a larger context by relating them to a number of aspects in the transportation and electricity generation sectors. It also provides a snapshot of the current energy landscape and discusses several research and development opportunities and pathways that could lead to a prosperous, sustainable and secure energy future for the world.

Opportunities and challenges for a sustainable energy future

Many different photovoltaic technologies are being developed for large-scale solar energy conversion. The wafer-based first-generation photovoltaic devices have been followed by thin-film solid semiconductor absorber layers sandwiched between two charge-selective contacts and nanostructured (or mesostructured) solar cells that rely on a distributed heterojunction to generate charge and to transport positive and negative charges in spatially separated phases. Although many materials have been used in nanostructured devices, the goal of attaining high-efficiency thin-film solar cells in such a way has yet to be achieved. Organometal halide perovskites have recently emerged as a promising material for high-efficiency nanostructured devices. Here we show that nanostructuring is not necessary to achieve high efficiencies with this material: a simple planar heterojunction solar cell incorporating vapour-deposited perovskite as the absorbing layer can have solar-to-electrical power conversion efficiencies of over 15 per cent (as measured under simulated full sunlight). This demonstrates that perovskite absorbers can function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures.

Efficient planar heterojunction perovskite solar cells by vapour deposition

Device Characteristics of CZTSSe Thin‐Film Solar Cells with 12.6% Efficiency

Although known since the late 19th century, organic–inorganic perovskites have recently received extraordinary research community attention because of their unique physical properties, which make them promising candidates for application in photovoltaic (PV) and related optoelectronic devices. This review will explore beyond the current focus on three-dimensional (3-D) lead(II) halide perovskites, to highlight the great chemical flexibility and outstanding potential of the broader class of 3-D and lower dimensional organic-based perovskite family for electronic, optical, and energy-based applications as well as fundamental research. The concept of a multifunctional organic–inorganic hybrid, in which the organic and inorganic structural components provide intentional, unique, and hopefully synergistic features to the compound, represents an important contemporary target.

Organic–Inorganic Perovskites: Structural Versatility for Functional Materials Design

Organic-inorganic hybrid materials promise both the superior carrier mobility of inorganic semiconductors and the processability of organic materials A thin-film field-effect transistor having an organic-inorganic hybrid material as the semiconducting channel was demonstrated Hybrids based on the perovskite structure crystallize from solution to form oriented molecular-scale composites of alternating organic and inorganic sheets Spin-coated thin films of the semiconducting perovskite (C(6)H(5)C(2)H(4)NH(3))(2)SnI(4) form the conducting channel, with field-effect mobilities of 06 square centimeters per volt-second and current modulation greater than 10(4) Molecular engineering of the organic and inorganic components of the hybrids is expected to further improve device performance for low-cost thin-film transistors

https://science.sciencemag.org/content/sci/286/5441/945.full.pdf

Organic-inorganic hybrid materials as semiconducting channels in thin-film field-effect transistors

The path towards a high-performance solution-processed kesterite solar cell ☆

2010 WILEY-VCH Verlag Gmb Chalcogenide-based solar cells provide a critical pathway to cost parity between photovoltaic (PV) and conventional energy sources. Currently, only Cu(In,Ga)(S,Se)2 (CIGS) and CdTe technologies have reached commercial module production with stable power conversion efficiencies of over 9 percent. Despite the promise of these technologies, restrictions on heavy metal usage for Cd and limitations in supply for In and Te are projected to restrict the production capacity of the existing chalcogen-based technologies to <100GWp per year, a small fraction of our growing energy needs, which are expected to double to 27 TW by 2050. Earth-abundant copper-zinc-tin-chalcogenide kesterites, Cu2ZnSnS4 and Cu2ZnSnSe4, have been examined as potential alternatives for the two leading technologies, reaching promising but not yet marketable efficiencies of 6.7% and 3.2%, respectively, by multilayer vacuum deposition. Here we show a non-vacuum, slurry-based coating method that combines advantages of both solution processing and particlebased deposition, enabling fabrication of Cu2ZnSn(Se,S)4 devices with over 9.6% efficiency—a factor of five performance improvement relative to previous attempts to use highthroughput ink-based approaches and >40% higher than previous record devices prepared using vacuum-based methods. To address the issue of cost, non-vacuum ‘‘ink’’-based approaches—both from solutions and suspensions—are being developed for chalcogenide-based absorber layer deposition to replace potentially more expensive vacuum-based techniques. True solutions allow intermixing of the constituents at a molecular level and the formation of smooth homogeneous films, as demonstrated with spin-coated CIGS absorber layers from hydrazine (N2H4) solutions. [11–13] The chemically reducing character of hydrazine stabilizes solutions of anions with direct metal-chalcogen bonding for select elements (e.g. Cu, In, Ga, Sn), without the necessity to introduce typical impurities (e.g., C, O, Cl). Suspension approaches employ solid particles designed to be deposited on a substrate and reacted or fused with each other, to form a desired crystalline phase and grain structure. Normally insoluble components can be deposited by this approach using typical liquid-based deposition (e.g., printing, spin coating, slit casting, spraying). Although high-quality large-grained absorber layers can be formed for selected systems using either solutionor particlebased deposition, numerous challenges confront each approach for more general deposition needs. Solution processing is limited by the solubility of many materials of interest (e.g., ZnSe1–xSx in hydrazine solvents—relevant for the deposition of Cu2ZnSnS4 or Cu2ZnSnSe4). In addition, volume contraction upon drying of solution-deposited layers creates stress in the film that may cause crack formation in thicker films. In suspension approaches, a common difficulty is achieving single-phase crystallization among the solid particles. Particle-based approaches (as well as some solution methods) typically require the addition of organic agents to improve wetting and particle dispersion, and to avoid film cracks and delamination. Most of these non-volatile organic additives introduce carbon contamination in the final layer. Because of these challenges, vacuum-based techniques have historically shown superior performance to liquid coating. In the case of the earth-abundant Cu2ZnSn(S,Se)4 materials, ink-based approaches have to date yielded at most <1.6% efficiency devices. Here we demonstrate an hybrid solution-particle approach, using the earth-abundant Cu2ZnSn(S,Se)4 system as an example, which enables fabrication of PV devices with over 9.6% power conversion efficiency. The slurry (or ink) employed for deposition comprises a Cu–Sn chalcogenide (S or S–Se) solution in hydrazine (see Experimental section), with the in situ formation of readily dispersible particle-based Zn-chalcogenide precursors, ZnSe(N2H4) (Figure 1a,d) or ZnS(N2H4) (Figure 1b). Thermogravimetric analysis (TGA) of the isolated selenide particle precursor shows decomposition at approximately 200 8C, with mass loss of about 20%, close to the theoretical value expected upon transition to pure ZnSe (Figure 1c,d). Deposition using this hybrid slurry successfully combines the advantages of solution and suspension deposition routes by use of solutions containing solid particles, wherein both components (i.e., solution and particle) contain metal and chalcogen elements that integrate into the final film. Using the hybrid slurry method (i) solubility limitations are resolved, as virtually any materials system can be constituted by a combination of solid and dissolved components; (ii) the dissolved components can be engineered as an efficient binding media for the particles, eliminating the need of separate organic binders; (iii) solid particles act as stress-relief and crack-deflection centers allowing the deposition of thicker layers than pure solution processes; and (iv) the intimate contact between the two phases allows rapid reaction and homogeneous phase formation. Complete conversion of all constituents of the spin-coated hybrid precursor films into a single-phase, highly crystalline Cu2ZnSn(S,Se)4 is achieved by annealing at 540 8C on a hot plate. Three main types of samples were targeted – high selenium content (A), intermediate sulfoselenide (B) and pure sulfide (C) –

David B. Mitzi

Papers

Device Characteristics of CZTSSe Thin‐Film Solar Cells with 12.6% Efficiency

Organic–Inorganic Perovskites: Structural Versatility for Functional Materials Design

Organic-inorganic hybrid materials as semiconducting channels in thin-film field-effect transistors

The path towards a high-performance solution-processed kesterite solar cell ☆

High‐Efficiency Solar Cell with Earth‐Abundant Liquid‐Processed Absorber