Teck Ming Koh

Bio: Teck Ming Koh is an academic researcher from Nanyang Technological University. The author has contributed to research in topics: Perovskite (structure) & Materials science. The author has an hindex of 23, co-authored 52 publications receiving 2687 citations.

Formamidinium-Containing Metal-Halide: An Alternative Material for Near-IR Absorption Perovskite Solar Cells

Abstract: Solid-state, solution processed solar-cells based on organic–inorganic methyl ammonium lead halide absorbers have achieved efficiencies in excess of 15%, which has superseded liquid dye sensitized cells, as well as various thin film-based photovoltaics. This report introduces a new metal-halide perovskite, based on the formamidinium cation (HC(NH2)2+), that displays a favorable band gap (1.47 eV) and represents a broader absorption compared to previously reported absorbers that contained the methylammonium cation (CH3NH3+). The high open-circuit voltage (Voc = 0.97 V) and promising fill-factor (FF = 68.7%) yield an efficiency of 4.3%, which make this material an excellent candidate for this new class of perovskite solar cell. This report also investigates the formation of a black trigonal (P3m1) perovskite polymorph and a yellow hexagonal nonperovskite (P63mc) polymorph. Further solar cell development would entail the stabilization of the black trigonal (P3m1) perovskite polymorph over the yellow hexagona...

Formamidinium tin-based perovskite with low Eg for photovoltaic applications

Abstract: A lead-free low bandgap organic–inorganic hybrid perovskite, formamidinium tin iodide, is utilized as a light absorbing layer in photovoltaics. This material has a bandgap of 1.41 eV which allows light harvesting from the near infrared region, making high photocurrents achievable. A power conversion efficiency of 2.10% was accomplished upon incorporating SnF2.

Perovskite Solar Cells: Beyond Methylammonium Lead Iodide

Abstract: Organic–inorganic lead halide based perovskites solar cells are by far the highest efficiency solution-processed solar cells, threatening to challenge thin film and polycrystalline silicon ones. Despite the intense research in this area, concerns surrounding the long-term stability as well as the toxicity of lead in the archetypal perovskite, CH3NH3PbI3, have the potential to derail commercialization. Although the search for Pb-free perovskites have naturally shifted to other transition metal cations and formulations that replace the organic moiety, efficiencies with these substitutions are still substantially lower than those of the Pb-perovskite. The perovskite family offers rich multitudes of crystal structures and substituents with the potential to uncover new and exciting photophysical phenomena that hold the promise of higher solar cell efficiencies. In addressing materials beyond CH3NH3PbI3, this Perspective will discuss a broad palette of elemental substitutions, solid solutions, and multidimensio...

Rb as an Alternative Cation for Templating Inorganic Lead-Free Perovskites for Solution Processed Photovoltaics

Abstract: Even though perovskite solar cells have reached 22% efficiency within a very short span, the presence of lead is a major bottleneck to its commercial application. Tin and germanium based perovskites failed to be viable replacements due to the instability of their +2 oxidation states. Antimony could be a possible replacement, forming perovskites with structure A3M2X9. However, solution processing of Cs, organic ammonium based Sb perovskites result in the formation of the dimer phase with poor charge transport properties. Here we demonstrate that Rb can template the formation of the desired layered phase irrespective of processing methodologies, enabling the demonstration of efficient lead-free perovskite solar cells.

Nanostructuring Mixed-Dimensional Perovskites: A Route Toward Tunable, Efficient Photovoltaics

Abstract: 2D perovskites is one of the proposed strategies to enhance the moisture resistance, since the larger organic cations can act as a natural barrier. Nevertheless, 2D perovskites hinder the charge transport in certain directions, reducing the solar cell power conversion efficiency. A nanostructured mixed-dimensionality approach is presented to overcome the charge transport limitation, obtaining power conversion efficiencies over 9%.

The emergence of perovskite solar cells

Abstract: Within the space of a few years, hybrid organic–inorganic perovskite solar cells have emerged as one of the most exciting material platforms in the photovoltaic sector. This review describes the rapid progress that has been made in this area.

High-performance photovoltaic perovskite layers fabricated through intramolecular exchange

Abstract: The band gap of formamidinium lead iodide (FAPbI3) perovskites allows broader absorption of the solar spectrum relative to conventional methylammonium lead iodide (MAPbI3). Because the optoelectronic properties of perovskite films are closely related to film quality, deposition of dense and uniform films is crucial for fabricating high-performance perovskite solar cells (PSCs). We report an approach for depositing high-quality FAPbI3 films, involving FAPbI3 crystallization by the direct intramolecular exchange of dimethylsulfoxide (DMSO) molecules intercalated in PbI2 with formamidinium iodide. This process produces FAPbI3 films with (111)-preferred crystallographic orientation, large-grained dense microstructures, and flat surfaces without residual PbI2. Using films prepared by this technique, we fabricated FAPbI3-based PSCs with maximum power conversion efficiency greater than 20%.

Compositional engineering of perovskite materials for high-performance solar cells

Abstract: Inorganic–organic lead halide perovskite could be efficient when used as the light-harvesting component of solar cells; here incorporation of methylammonium lead bromide into formamidinium lead iodide stabilizes the perovskite and improves the power conversion efficiency of the solar cell up to 17.9 per cent. Inorganic–organic lead halide perovskites are currently attracting considerable interest for solar-cell applications. Most of the best performing perovskite solar cells to date have made use of methylammonium-based perovskites; formamidinium-based perovskites have also shown promise, but are not as stable. Now Nam Joong Jeon and colleagues show that the formamidinium-based perovskites can be stabilized by the addition of some methylammonium-based perovskite, and that solar cells incorporating the resulting compositionally tuned materials can reach new heights of efficiency. Of the many materials and methodologies aimed at producing low-cost, efficient photovoltaic cells, inorganic–organic lead halide perovskite materials1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17 appear particularly promising for next-generation solar devices owing to their high power conversion efficiency. The highest efficiencies reported for perovskite solar cells so far have been obtained mainly with methylammonium lead halide materials1,2,3,4,5,6,7,8,9,10. Here we combine the promising—owing to its comparatively narrow bandgap—but relatively unstable formamidinium lead iodide (FAPbI3) with methylammonium lead bromide (MAPbBr3) as the light-harvesting unit in a bilayer solar-cell architecture13. We investigated phase stability, morphology of the perovskite layer, hysteresis in current–voltage characteristics, and overall performance as a function of chemical composition. Our results show that incorporation of MAPbBr3 into FAPbI3 stabilizes the perovskite phase of FAPbI3 and improves the power conversion efficiency of the solar cell to more than 18 per cent under a standard illumination of 100 milliwatts per square centimetre. These findings further emphasize the versatility and performance potential of inorganic–organic lead halide perovskite materials for photovoltaic applications.

Cesium-containing triple cation perovskite solar cells: improved stability, reproducibility and high efficiency

Abstract: Today's best perovskite solar cells use a mixture of formamidinium and methylammonium as the monovalent cations. With the addition of inorganic cesium, the resulting triple cation perovskite compositions are thermally more stable, contain less phase impurities and are less sensitive to processing conditions. This enables more reproducible device performances to reach a stabilized power output of 21.1% and ∼18% after 250 hours under operational conditions. These properties are key for the industrialization of perovskite photovoltaics.

Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes.

Abstract: Organic-inorganic hybrid perovskites are emerging low-cost emitters with very high color purity, but their low luminescent efficiency is a critical drawback. We boosted the current efficiency (CE) of perovskite light-emitting diodes with a simple bilayer structure to 42.9 candela per ampere, similar to the CE of phosphorescent organic light-emitting diodes, with two modifications: We prevented the formation of metallic lead (Pb) atoms that cause strong exciton quenching through a small increase in methylammonium bromide (MABr) molar proportion, and we spatially confined the exciton in uniform MAPbBr3 nanograins (average diameter = 99.7 nanometers) formed by a nanocrystal pinning process and concomitant reduction of exciton diffusion length to 67 nanometers. These changes caused substantial increases in steady-state photoluminescence intensity and efficiency of MAPbBr3 nanograin layers.