PhD student, Monash University
Metal halide perovskites are an emerging class of layered semiconductors with unique electronic and optical properties that allow for low-cost, highly efficient optoelectronic applications, including photovoltaics, light-emitting diodes (LEDs), photodetectors and solar-to-fuel energy conversion devices. The power conversion efficiency of perovskite solar cells has quickly risen to 22.1% over the past six years. Their high optical emission efficiency makes these perovskites suitable for use in optoelectronic and photonic devices, such as LEDs, photodetectors, waveguides and lasers. For instance, perovskite LEDs have achieved external quantum efficiency over 11%, which is already comparable to that of state-of-the-art organic LEDs. Photodetectors based on planar perovskite films exhibit high gain, fast response time and good flexibility, showing great promise as next-generation highly efficient photodetectors. Perovskites are also considered to be a class of layered materials, whose optical properties can be controlled by varying the number of layers (thickness), particularly at thicknesses lower than their exciton Bohr radius (~few nanometres). It has been known that the rapid progress in graphene has led to exploration of many two-dimensional (2D) materials such as hexagonal boron nitride, transition metal dichalcogenides and black phosphorus, etc. In particular, 2D semiconductor materials are of huge benefit due to strong in-plane quantum confinement and sizable bandgap, which are desired for many optoelectronic applications. Compared with conventional 2D materials that are covalent semiconductors, 2D perovskites are ionic materials, giving them special properties of their own. 2D perovskites can exhibit enhanced fluorescence emission decay rates and higher exciton binding energies compared with their bulk counterparts. In addition, the large surface area of 2D sheets enables stronger interaction with other 2D materials for efficient energy transfer. Controlling of the electronic characteristics of 2D perovskite semiconductors is thus of great importance for future low-energy electronics technology.
Abstract: Metal-halide perovskites have been hailed as remarkable materials for photovoltaic devices and, recently, their star has also been on the rise in optoelectronics and photonics. In particular, the optical properties of a metal-halide perovskite can be widely manipulated once its bulk structure has been reduced to a low-dimensional structure, allowing multiple functionalities of light generation, emission, transmission, and detection to be realized in one material. In this paper, we highlight the recent advances in the synthesis of low-dimensional metal-halide perovskites and their unique properties as well as their novel optoelectronic and photonic applications. It is anticipated that this review can serve as an overview and evaluation of state-of-the-art synthesis techniques as well as nanoscale optoelectronics and photonics based on low-dimensional perovskite nanocrystals.
Pub.: 03 Oct '16, Pinned: 11 Oct '17
Abstract: Even though the nonlinear optical effects of solution processed organic-inorganic perovskite films have been studied, the nonlinear optical properties in two-dimensional (2D) perovskites especially their applications for ultrafast photonics are largely unexplored. In comparison to bulk perovskite films, 2D perovskite nanosheets with small thickness of a few unit cells are more suitable for investigating the intrinsic nonlinear optical properties because bulk recombination of photo-carriers and the nonlinear scattering are relatively small. In this research, we systematically investigated the nonlinear optical properties of 2D perovskite nanosheets derived from a combined solution process and vapour phase conversion method. It was found that 2D perovskite nanosheets have stronger saturable absorption properties with large modulation depth and very low saturation intensity compared with bulk perovskite films. Using an all dry transfer method, we constructed a new type of saturable absorber device based on single piece 2D perovskite nanosheet. Stable soliton state mode-locking was achieved and ultrafast picosecond pulses were generated at 1064 nm. This work is likely to pave the way for ultrafast photonic and optoelectronic applications based on 2D perovskites.
Pub.: 21 Mar '17, Pinned: 11 Oct '17
Abstract: Organo-lead halide perovskites as a new class of exceptional optoelectronic materials has been found use in many applications. However, conventional methods for forming single crystals of OHPs afford limited control over the product morphology, rendering the assembly of defined microstructures difficult. We overcame this by synthesising for the first time (MA)[PbBr3]·DMF (1), and demonstrating its facile transformation into monocrystalline MAPbBr3 microplatelets, which exhibit excellent waveguiding porperty with an ultra-low propagation loss of 0.04 dB μm-1 and can be further tailored into a variety of waveguide based photonic devices. An efficient electro-optical modulator consisting of a MAPbBr3 non-linear arc waveguide was demonstrated, exhibiting a 98.4% PL intensity modulation with an external voltage of 45 V. This novel approach and the demonstration of effective waveguiding will pave the way for developing a wide range of photonic devices based on organo lead halide perovskites.
Pub.: 10 Jun '17, Pinned: 11 Oct '17
Abstract: Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials.
Pub.: 26 Sep '15, Pinned: 11 Oct '17
Abstract: The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and mixed halide anions. The concentration of defect states, which reduce a cell's performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.
Pub.: 01 Jul '17, Pinned: 11 Oct '17