Perovskite-Info: the perovskite experts

Researchers from Rutgers University, University of Minnesota and University of Texas at Dallas in the U.S have discovered a new type of electric field effect that can control light emission from perovskite devices.

The electric field effect usually refers to the modulation of electrical conductivity in a semiconductor by means of an applied voltage to a gate electrode and forms the basis of modern digital electronics. In a conventional field effect transistor (FET), the conductivity of a semiconductor layer can be turned on or off or gradually ramped up or down. Now, the research team has found that the photoluminescence (PL) of a perovskite device can be modulated in a similar manner. “Our work reports a novel type of field effect in which PL, rather than conductivity, is tuned by an ‘electric knob’ – the gate voltage,” explains Vitaly Podzorov, who led the research.

A recent joint-research co-led by City University of Hong Kong (CityU) and Shanghai University has developed an efficient fabrication approach for all-inorganic perovskite films with better optical properties and stability, enabling the development of high color-purity and low-cost perovskite LEDs with a high operational lifetime.

The team has found that using cesium trifluoroacetate (TFA) as the cesium source in the one-step solution coating, instead of the commonly used cesium bromide (CsBr), enables fast crystallization of small-grained CsPbBr₃ perovskite crystals, forming the smooth and pinhole-free perovskite films. This is because the interaction of TFA- anions with Pb2+ cations in the CsPbX3 precursor solution greatly improves the crystallization rate of perovskite films and suppresses surface defects.

A team of researchers from UC San Diego, Georgia Institute of Technology, Purdue University, MIT and Argonne National Laboratory has reported new findings on perovskites, that could pave the way to developing low-cost, high-efficiency solar cells. Using high-intensity X-ray mapping, they explain why adding small amounts of cesium and rubidium salt improves the performance of lead-halide perovskites.

“Perovskites could really change the game in solar. They have the potential to reduce costs without giving up performance. But there’s still a lot to learn fundamentally about these materials,” said David Fenning, a professor of nanoengineering at the University of California San Diego and co-senior author of the study. “We’re looking deeper into some of the state-of-the-art chemistries to understand what drives perovskite performance and why they work so well.”

Researchers at the Germany-based Helmholtz Center Berlin (HZB) have announced a thin-film solar cell made of perovskite and copper-indium-gallium-selenide (CIGS) with an efficiency of 21.6%.

The HZB researchers said they used a simple, robust production process suitable for scaling up. Rutger Schlatmann, director of the HZB’s Institute PVcomB, spoke of an “enormous step in the direction of commercial production”. The HZB team’s tandem cell could theoretically reach an efficiency of more than 30%, according to the researchers.

Researchers at Solliance, in collaboration with MiaSole Hi-Tech Corp., have designed a flexible solar cell with an impressive power conversion efficiency of 21.5%. The solar cell combines two thin-film solar cell technologies into a 4 terminal tandem solar cell stack: a top flexible semi-transparent perovskite solar cell with a bottom flexible copper indium gallium selenide (CIGS) cell.

A tandem solar cell, which combines a perovskite and a Cu(In,Ga)Se2 (CIGS) cell, has the potential for high conversion efficiency exceeding single junction solar cell performance thanks to tunable and complementary bandgaps of these individual thin film solar cells. CIGS technology has a proven track record as a high efficiency and stable solar technology, and has entered high volume manufacturing in multi-GW scale around the world. CIGS technology has been successfully used to produce high efficiency flexible and lightweight cells and modules, which address markets where heavy and rigid panels cannot be used. Perovskite solar cells, promise low cost solar technology based on abundant materials. Combining both technologies in a flexible and lightweight package expands the horizon of high performance, flexible, and customizable solar technology.

Researchers from the University of Potsdam, Humboldt University, Helmholtz-Zentrum Berlin and Technical University Berlin have recently published a paper on perovskite solar cell improvement with the addition of Strontium.

(a) cell structure in the study (b) perovskite structure used here, indicating how Sr can replace Pb

The team managed to reach record Voc for pin-type perovskite solar cells and elucidated the effect of the Strontium incorporation.

Researchers at Tokai University report a systematic study on the effects that using different forms of titanium oxide in planar perovskite solar cells has on the performance of the devices.

The team from Tokai university focused on the electron-transport layer. The material of choice for this component is often titanium oxide, whose electronic structure makes it easy to collect electrons from the perovskite layer. Titanium oxide has several crystal polymorphs including anatase, brookite, and rutile. They have different structures and properties and their distinct morphologies influence the quality of the perovskite layer, so the choice of polymorph influences the overall performance of the solar cell. This is why understanding this influence is important for optimizing the efficiency of devices.