July 2016

Researchers at Purdue University have found that nickel-based perovskites have exceptional properties for use as solid electrolytes in fuel cells. Unlike conventional electrolytes, these nickel-based perovskites are chemically stable in the fuel cell's environment, which could lead to higher performing and longer lasting fuel cells.

Schematic of the perovskite samarium nickelate (SNO)-electrolyte solid-oxide fuel cell.

Solid-oxide fuel cells are considered as one of the most efficient types of fuel cells. They typically use polymers or ceramics as an electrolyte, but finding an effective solid electrolyte'one that conducts protons but blocks electrons'at low operating temperatures of 300'500°C has been a challenge. Most materials, when exposed to low pressure, start to lose oxygen and become electron conductors; The electrolyte separator becomes leaky so it can short circuit the fuel cell or it can start to crack and allow fuel to mix with oxygen.

A research group at the Japan-based National Institute for Materials Science (NIMS) reported the achievement of energy conversion efficiency exceeding 18% using standard size (1 cm2) perovskite solar cells. This measurement was made by the Calibration, Standards and Measurement Team at the Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST)'an internationally recognized independent organization for solar cell evaluation.

The research group developed high-quality crystal particles that constitute a perovskite layer by adjusting the ratio of different cations in the layer and by substituting some of the iodine with bromine. Consequently, they were able to efficiently extract electrons and holes formed by exposure to light, and succeeded in increasing the short-circuit current density to more than 21 mA/cm2. Furthermore, they accurately controlled the thickness of layers in solar cells such as perovskite and electron transport layers and thereby reduced electrical resistance within the solar cells. As a result, they were able to reach this increased conversion efficiency of 18.2%.

Solar-Tectic, a thin-film specialist with patented technology primary focused on developing highly textured, single crystal semiconductor films on glass or other inexpensive substrates, presented a paper at the "Fifth International Symposium on Energy Challenges and Mechanics (ECM5) - working on small scales" in Inverness, Scotland, making public for the first time details of its perovskite/crystalline silicon thin-film tandem solar cell technology for highly efficient and inexpensive solar cells.

While reports of perovskite/silicon tandem solar cells are common, it would seem that there have been much less mentions of perovskite/thin-film silicon. Crystalline thin-film silicon promises to be less expensive than silicon wafer technology due to low temperature processing and less material use. Also, the entire process is non-toxic since tin (Sn) is used in the perovskite material, rather than lead (Pb).

Researchers from Los Alamos National Laboratory, Rice University and Northwestern University have been working on modifying perovskites' manufacturing technique and producing a new variety of 2D layered perovskite with exceptional strength and increased power transformation capability.

Three types of large-area solar cells made out of two-dimensional perovskites. At left, a room-temperature cast film; upper middle is a sample with the problematic band gap, and at right is the hot-cast sample with the best energy performance.

Using a spin-casting technique, the team managed to create layered crystals whose electrons flow vertically down the material without being blocked, midlayer, by organic cations. The researchers stated that 'the new 2D perovskite is both more efficient and more stable, both under constant lighting and in exposure to the air, than the existing 3D organic-inorganic crystals'.

Researchers at Nanyang Technological University in Singapore have fabricated high-performance green light-emitting diodes based on colloidal organometal perovskite nanoparticles. The devices have a maximum luminous efficiency of 11.49 cd/A, a power efficiency of 7.84 lm/W and an external quantum efficiency of 3.8%. This value is said to be about 3.5 times higher than that of the best colloidal perovskite quantum-dot-based LEDs previously made.

The team developed a simple way to make a series of colloidal (CH3NH3)PbX3 nanoparticles with an amorphous structure that can be tuned to emit light in the ultraviolet to near-infrared range. They studied the photoluminescence properties of the nanoparticles and found that the PLQE of the perovskite NP film is much higher than that of the bulk film. They then made the highly efficient green LED.

Researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory have found that it may be possible to boost energy conversion rates perovskite-based solar modules by as much as 40%.

Using an atomic microscope, the researchers observed multifaceted surfaces in perovskite solar cells. Some of the grains, which were about 200 microns in width, had sharply formed multi-angled facets, while others were poorly formed. The poorly formed facets had energy conversion efficiencies approaching 31%, which beats today's most optimistic photovoltaic efficiency rates of around 22%.