Introducing Perovskite Solar Cells to Undergraduates

Dimension-Controlled Synthesis of Hybrid-Mixed Halide Perovskites for Solar Cell Application

Despite the rapid improvement of photovoltaic (PV) efficiency in hybrid organic-inorganic metal halide perovskites (HOIPs), the fabrication procedure of a compact thin film in a large-area application is still a tedious work. Apart from the quality of the thin film, the stability of the perovskite materials and the expensive organic hole transport layer (HTL) within the HOIP-based PV device are the major issues that need to be addressed prior to their commercialization. Herein, a unique glass rod-based facile fabrication technique for producing a compact and stable thin film utilizing a mixed-halide-based perovskite precursor solution is demonstrated. The fabricated devices deliver high photoconversion efficiency (PCE) without the use of any HTL and show an excellent stability under ambient conditions. By varying the organic CH3NH3I (MAI) and inorganic PbBr2 content, perovskite materials with different dimensions, i.e., 3D, 2D, and 1D, are synthesized to produce an active layer for PV devices. Although a 2D single-halide perovskite is reported earlier, herein two different mixed-halide 2D perovskites, i.e., MA2PbI2Br2 and MAPb2IBr4, are synthesized successfully, and their performance is compared in detail along with that of 1D and 3D mixed-halide perovskites. The facile synthesized mixed-halide 2D-based MA2PbI2Br2 perovskite shows a PCE of 10.14% with a high stability of 92% after 100 days without encapsulation, which is much superior as compared to that of the mixed-halide 3D MAPbIBr2. The semiconducting behavior as well as the nature of the bandgap of the synthesized compounds is examined by pursuing density functional theory calculations. Specifically, the role of iodine doping to modify the electronic band structure is investigated, and introduction of iodine is found to reduce the effective masses of both electrons and holes in the perovskite material.

New accurate molecular dynamics potential function to model the phase transformation of cesium lead triiodide perovskite (CsPbI3)

Inorganic metallic halide perovskites and cesium lead triiodide, CsPbI₃, in particular, have gained enormous attention recently due to their unique photovoltaic properties and low processing temperatures. However, their structural stability and phase transition still need an in-depth investigation to better optimize their optoelectronic properties. For sake of time and cost, Classical Molecular Dynamics (CMD) and first principles calculations are being used to predict the structure stability and phase transition of CsPbI₃. The major challenge of CMD is the choice of proper interatomic potential functions. In this paper, a new hybrid force field is being introduced, which integrates the embedded atomic potentials of Cs-Cs and Pb-Pb with Buckingham-Coulomb potentials. The Buckingham-Coulomb interatomic potential was solely employed as well. The outputs from both force fields were reported and compared to the experimental values. In fact, the new Hybrid Embedded Atomic Buckingham-Coulomb (EABC) potential reproduces, with a great degree of accuracy (within 2.5%), the structural properties, such as the radial distribution functions, interatomic separation distances, and the density. Also, it detects the phase transformation from an orthorhombic into a cubic crystal structure and the melting temperature at 594 K and 750 K respectively which agrees with the experimental values to within 1%. The new proposed hybrid potential proved to be accurate so it could potentially be used to infer the structure stability and the mechanical and thermal properties of the pure inorganic halide perovskites and the mixed halide perovskites as well which are used in various applications.

Chemical Trends in the Thermodynamic Stability and Band Gaps of 980 Halide Double Perovskites: A High-Throughput First-Principles Study

The chemical trends in the thermodynamic stability and band gaps of 980 A₂B⁺B³⁺X₆ halide double perovskites are revealed based on high-throughput first-principles calculations. To accurately predict the stability with respect to phase decomposition, all known metal halides in the Materials Project database are considered as the competing compounds. The energies above the convex hull show that only 112 of 980 double perovskites are stable and 27 double perovskites that had been predicted to be stable in the literature are actually unstable after considering more competing compounds. The stability of these double perovskites is determined mainly by A, X, and B⁺ elements and increases gradually as A becomes heavier (from Li to Cs) and X becomes lighter (from I to F). The band gaps are determined mainly by X, B⁺, and B³⁺ elements, decreasing monotonically as X becomes heavier while changing nonmonotonically as B⁺ and B³⁺ change. These chemical trends provide clear instructions for the design of double perovskites with good stability and suitable band gaps for various applications, i.e., through choosing heavier A cations (e.g., large organic cations), stable double perovskites can be designed with band gaps tunable in a wide range of 0-7 eV (infrared to ultraviolet); however, through choosing light X anions, stable double perovskites can be designed with only wide band gaps.

Lead-free double perovskites Cs2InCuCl6 and (CH3NH3)2InCuCl6: electronic, optical, and electrical properties

Searching for alternatives to lead-containing metal halide perovskites, we explored the properties of indium-based inorganic double perovskites Cs₂InMX₆ with M = Cu, Ag, Au and X = Cl, Br, I, and of its organic-inorganic hybrid derivative MA₂InCuCl₆ (MA = CH₃NH₃⁺) using computation within Kohn-Sham density functional theory. Among these compounds, Cs₂InCuCl₆ and MA₂InCuCl₆ were found to be potentially promising candidates for solar cells. Calculations with different functionals provided the direct band gap of Cs₂InCuCl₆ between 1.05 and 1.73 eV. In contrast, MA₂InCuCl₆ exhibits an indirect band gap between 1.31 and 2.09 eV depending on the choice of exchange-correlation functional. Cs₂InCuCl₆ exhibits a much higher absorption coefficient than that calculated for c-Si and CdTe, common semiconductors for solar cells. Even MA₂InCuCl₆ is predicted to have a higher absorption coefficient than c-Si and CdTe across the visible spectrum despite the fact that it is an indirect band gap material. The intrinsic charge carrier mobilities for Cs₂InCuCl₆ along the L-Γ path are predicted to be comparable to those for MAPbI₃. Finally, we carried out calculations of the band edge positions for MA₂InCuCl₆ and Cs₂InCuCl₆ to offer guidance for solar cell heterojunction design and optimization. We conclude that Cs₂InCuCl₆ and MA₂InCuCl₆ are promising semiconductors for photovoltaic and optoelectronic applications.

Organic-inorganic hybrid lead halide perovskites for optoelectronic and electronic applications

Organic and inorganic hybrid perovskites (e.g., CH(3)NH(3)PbI(3)), with advantages of facile processing, tunable bandgaps, and superior charge-transfer properties, have emerged as a new class of revolutionary optoelectronic semiconductors promising for various applications. Perovskite solar cells constructed with a variety of configurations have demonstrated unprecedented progress in efficiency, reaching about 20% from multiple groups after only several years of active research. A key to this success is the development of various solution-synthesis and film-deposition techniques for controlling the morphology and composition of hybrid perovskites. The rapid progress in material synthesis and device fabrication has also promoted the development of other optoelectronic applications including light-emitting diodes, photodetectors, and transistors. Both experimental and theoretical investigations on organic-inorganic hybrid perovskites have enabled some critical fundamental understandings of this material system. Recent studies have also demonstrated progress in addressing the potential stability issue, which has been identified as a main challenge for future research on halide perovskites. Here, we review recent progress on hybrid perovskites including basic chemical and crystal structures, chemical synthesis of bulk/nanocrystals and thin films with their chemical and physical properties, device configurations, operation principles for various optoelectronic applications (with a focus on solar cells), and photophysics of charge-carrier dynamics. We also discuss the importance of further understanding of the fundamental properties of hybrid perovskites, especially those related to chemical and structural stabilities.

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.