Lead-free

Scientists at the University of California at Berkeley and the US Department of Energy's Lawrence Berkeley National Laboratory have developed a perovskite-structured ferroelectric compound that might be suitable for the production of lead-free perovskite solar cells.

“The new ferroelectric material – which is grown in the lab from cesium germanium tribromide (CsGeBr₃ or CGB) – opens the door to an easier approach to making solar cell devices,” the team said. “Unlike conventional solar materials, CGB crystals are inherently polarized, where one side of the crystal builds up positive charges and the other side builds up negative charges, no doping required.”

Scientists at the University of California San Diego, Lawrence Berkeley National Laboratory, Stanford University, Los Alamos National Laboratory, Korea's Yonsei University and Daegu Gyeongbuk Institute of Science and Technology have developed a novel perovskite solar cell, made of a lead-free low-dimensional perovskite material with a superlattice crystal structure. The material exhibits efficient carrier dynamics in three dimensions, and its device orientation can be perpendicular to the electrodes. Materials in this particular class of perovskites have so far only exhibited such dynamics in two dimensions—a perpendicularly orientated solar cell has never been reported.

The team reported that thanks to its specific structure, this new type of superlattice solar cell reaches an efficiency of 12.36%, which is the highest reported for lead-free low-dimensional perovskite solar cells (the previous record holder’s efficiency is 8.82%). The new solar cell also has an unusual open-circuit voltage of 0.967 V, which is higher than the theoretical limit of 0.802 V. Both results have been independently certified.

Scientists at Nanyang Technological University in Singapore (NTU) and Tsinghua University have developed a stretchable and waterproof ‘fabric’ that turns energy generated from body movements into electrical energy. The fabric contains a polymer that, when pressed or squeezed, converts mechanical stress into electrical energy. It is also made with stretchable spandex as a base layer and integrated with a rubber-like material to keep it strong, flexible, and waterproof.

The team showed that tapping on a 3cm by 4cm piece of the new fabric generated enough electrical energy to light up 100 LEDs. The fabric can withstand washing, folding and crumpling without performance degradation, and it could maintain stable electrical output for up to five months, demonstrating its potential for use as a smart textile and wearable power source.

A research team, led by Professor Iván Mora Seró from the Institute of Advanced Materials (INAM) of the Universitat Jaume I of Castelló, has improved the efficiency and durability of tin perovskite solar cells. The cells presented in the recent study exceeded 1,300 hours of operational stability, thanks to the incorporation of additives in the preparation of the devices.

Tin-based halide perovskites are being studied as potential candidates for lead-free perovskite solar cells. In the case of tin, an efficiency of more than 14% has been achieved so far, but it has major stability problems. This new work has introduced a combination of dipropylammonium iodide and sodium borohydride, two additives that have made it possible to prepare devices with PCEs of more than 10%, which boast greater stability and have maintained 96% of the initial PCE after 1,300 hours under solar illumination in a nitrogen atmosphere.

A team from Israel's Technion Institute of Technology has announced the development of self-healing perovskite nanocrystals.

Having to frequently replace electronics due to malfunctioning of materials is unavoidable today, since every device suffers from degradation as a result of defects that accumulate during use over time. This generates, in addition to customer frustration and costs, a heavy environmental footprint.

An international research team from TU Dort­mund Uni­ver­sity, the Russian Academy of Sciences and ETH Zürich has dis­cov­ered that the electron dynamics in perovskite crystals are largely determined by lead. This discovery suggests that replacing this element could enable better control of the crystals' material properties.

TU Dort­mund Uni­ver­sity Professor Dmitri Yakovlev's group investigated ultrafast interaction processes between optically excited charge carriers and their surroundings in perovskite crystals. The team was able to show that the magnetic properties can be regulated on an ultrafast time scale through the use of optical pulses with a duration of trillionths of a second. This proof that they can be con­trolled is of particular interest for possible new applications.

Researchers from University of North Carolina, North Carolina State University and Chinese Academy of Sciences have fabricated a mini perovskite solar module using a novel encapsulation technique based on the use of a self-healable, lead-adsorbing ionogel that prevents lead leakage and improves stability. The solar module has an area of 31.5cm² and has a reported efficiency of 22.9%.

Ionogel microstructure and lead adsorption mechanism. Image from article

The scientists explained that ionogel sealants were applied on the panel's front glass and between electrode and encapsulation glass, with the 100μm-thick inonogel being able to hold the shattered glass together even if the glass breaks. This is claimed to effectively suppress lead leakage from broken modules after hail test or compression by car wheels, and soaking in water for 45 days.

Unlike the narrow band emission based on free excitons in lead-perovskite nanocrystals (NCs), the low electronic dimensionality in lead-free double perovskite NCs can lead to self-trapped excitons (STEs), generating a broadband emission. To date, how the singlet/triplet STEs influence the photoluminescence properties and whether triplet STEs can generate efficient emission in double-perovskite NCs has been unclear.

A research team, led by Prof. Han Keli and Yang Bin from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences, recently synthesized double perovskite nanocrystals with bright photoluminescence emission based on triplet STEs.

A research group, led by Prof. Han Keli from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), in collaboration with Prof. Miao Xiangyang's group from Shanxi Normal University, recently explored the colloidal synthesis of all-inorganic rare-earth-based double perovskite NCs with NIR emission, and revealed their exciton dynamics.

Previous studies mainly focused on the photoluminescence (PL) in the visible region, and those on the near-infrared (NIR) PL of lead-free perovskite NCs are rare.

Researchers from the Hong Kong University of Science and Technology (HKUST) have developed an inexpensive, lightweight, and lead-free photo-battery that has dual functions in harvesting solar energy and storing energy on a single device. This could enable users to charge a battery under the sun, without having to plug the device into the wall.

Despite the theoretical potential of such photo-batteries, in reality it seems that the poor interface between materials tends to create problems with charge transport, greatly reducing the efficiency in comparison to the simple system of a solar cell wired to an external battery. A team led by Prof. Jonathan Eugene Halpert, Assistant Professor from the Department of Chemistry at HKUST, has made advancements towards developing more efficient photo-batteries by using perovskites.