August 2016

Researchers at MIT tackled the known problem of degradation suffered when perovskite oxides, promising candidates for electrodes in energy conversion devices like fuel cells, are exposed to water or gases such as oxygen or carbon dioxide at elevated temperatures.

The scientists explain that this degradation occurs as the surfaces of these perovskites get covered up by a strontium oxide'related layer, and this layer is insulating against oxygen reduction and oxygen evolution reactions, which are critical for the performance of fuel cells, electrolyzers and thermochemical fuel production. This layer on the electrode surface is detrimental to the efficiency and durability of the device, causing the surface reactions to slow down by more than an order of magnitude.

Researchers from the Graphene Flagship, working at the Istituto Italiano di Tecnologia (IIT) and the University of Rome Tor Vergata, show that interface engineering with layered materials is important for boosting perovskite solar cell performance and that the lifetime of perovskite solar cells is significantly enhanced by using few-layer molybdenum disulphide (MoS2) flakes (a semiconductor material with a layered structure).

The team managed to significantly enhance the stability of perovskite solar cells (PSCs) by including few-layer MoS2 flakes as an active buffer layer in the cell design. These PSCs retain 93% of the initial light conversion efficiency after 550 h, compared to only 66% for cells without the MoS2 buffer layer. This represents an important step towards viable PSCs, especially as the addition of the MoS2 interface layer is compatible with low-cost solution processing techniques.

A team of researchers from the King Abdullah University of Science and Technology (KAUST) of the Kingdom of Saudi Arabia has reported a perovskite-based phosphor-based white light converter with a modulation bandwidth around 40 times higher than common LED phosphors. This result could put an end to today's VLC bottleneck when using white LEDs.

By mixing solution-processed CsPbBr3 perovskite nanocrystals (NCs) with a conventional red phosphor, they obtained what they describe as a perovskite-based phosphor white light converter with a modulation bandwidth of 491MHz, which could support high data rate up to 2 Gbit/s, much faster than Wi-Fi. In addition to exhibiting a shorter excited lifetime, the red phosphor and perovskite composite material yields a white light with a high colour rendering index of 89 and a correlated colour temperature of 3236 K, which makes the white LED suitable for comfort lighting applications.

Dyesol recently secured a £800,000 ($1.05 million) grant by the U.K.'s Engineering and Physical Sciences Research Council (EPSRC) for the continued research in the optimization of charge carrier mobility in nanoporous metal oxide films and will enable the Australian organic cell developer to better understand the impact of halide modified titania on Perovskite cell performance.

The EPSRC is the U.K.'s main agency for funding research in engineering and the physical sciences, and this grant will be delivered specifically to Dyesol UK, Cristal and the University of York. The grant monies will, Dyesol said, help support better understanding of the chemistry of the improved electron capture and transport technique.

Researchers at the University of Groningen provided new insight into hybrid perovskite traps - the loss of electric charges that happens in both silicon and perovskite, and reduces the efficiency of photovoltaic cells.

The new insight happened by chance. The researchers placed a perovskite crystal in a vacuum chamber in an attempt to cool it down and while pumping out the air, a laser was left on, that excited the crystal. This laser light produced electronic charges in the crystal, which emitted light when they recombined. In this instance the crystal should have emitted green light, but surprisingly, when the air was removed from around it, the green light disappeared too. However, when the air was let back in again, the light emission was restored. So apparently, without air, most charges disappear into the traps.

Department of Energy (DoE) funded researchers investigated the electronic properties of 2D hybrid organic-inorganic perovskite sheets, as an alternative to graphene and other materials. The researchers reported that such perovskites could rival graphene in PV applications, since the 2D crystals exhibited efficient photoluminescence, were easier to grow than graphene and it's possible to dope it to make the various varieties of ionic semiconductors needed to beat other 2D materials with tunable electronic/photonic properties.

Scientists created these new forms of hybrid organic-inorganic perovskites in atomically thin 2D sheets and first showed how they hold promise as semiconductor materials for photovoltaic applications. Next they showed how they could serve as an alternative to other 2D semiconductors that are widely studied as potential successors to silicon in future electronic devices.

The University at Buffalo and Rensselaer Polytechnic Institute (RPI) won a $225,000 grant from the Department of Energy's SunShot Initiative to investigate chalcogenide perovskites.

The funds will go towards helping the team develop techniques for fabricating thin film solar devices made from such perovskite materials. The researchers plan to optimize the electronic and optical properties of the materials through defect engineering.

Researchers at the University of Virginia and Cornell University have been working on self-assembling metal halide perovskite thin film solar cells for several years. They have recently developed a formulation that raises the hope that commercialization will be possible soon, hopefully within next five years. Such solar panels will simply be sprayed onto a surface, and self-assemble into a high-quality thin film automatically as they dry.

The scientists used high-intensity x-rays to observe the crystallization process to understand precisely how the low temperature self-assembly from a liquid solution to a solid single-crystal film works and observed the high-speed growth of crystallization of metal halide perovskites in real time on the atomic level. By adding different chemicals to the solution, they demonstrated how to control the orientation and speed of crystallization.

Researchers taking part in a project supported by the Austrian Science Fund FWF, in cooperation with a team of researchers from the Weizmann Institute of Science in Israel and Drexel University in Philadelphia, US, have shown that lead-halide perovskite materials' instability can be considerably reduced through high levels of doping with chloride ions.

The scientists discovered that certain perovskites can hold high levels of chloride ions, and that this enhances the stability of the functional material under certain conditions by up to two orders of magnitude. They examined cesium-lead-iodide perovskites, where a known issue is the stability of the functional phase of this material - under certain conditions, a phase transition occurs and the excellent photovoltaic properties are lost almost immediately. Previous experiments on perovskites (including chloride instead of iodide ions) suggest that doping the material with chloride may enhance its stability. However, achieving this in practice proved to be extremely difficult.

A research team at the Korea Advanced Institute of Science and Technology (KAIST) and Sungkyunkwan University developed a perovskite-based solar cell that is semi-transparent, highly efficient and functions very effectively as a thermal-mirror.

The team has developed a top transparent electrode (TTE) that works well with perovskite solar cells. In most cases, a key to success in realizing semi-transparent solar cells is to find a TTE that is compatible with a given photoactive material system, which is also the case for perovskite solar cells. The proposed TTE is based on a multilayer stack consisting of a metal film sandwiched between a high refractive-index (high-index) layer and an interfacial buffer layer. This TTE, placed as a top-most layer, can be prepared without damaging ingredients used in perovskite solar cells.