KAUST team finds that small changes may cause big improvements in perovskite solar cells

Researchers from the KAUST Solar Center have monitored the impact of compositional changes on the structural organization and photovoltaic properties of perovskite thin films in situ. The team has reached a conclusion that may benefit perovskite solar cells in the future - that changes in composition affect light-harvesting layer crystallization and perovskite solar cell efficiency.

Sequence of fabrication of a perovskite thin film from precursor solution to solid filmimageSequence of fabrication of a perovskite thin film from precursor solution to solid film via the spin-coating deposition process. Image by KAUST

Solar cell performance and stability depend on the morphology of the thin films, especially their ability to crystallize in the so-called photoactive α-phase. Perovskites that contain lead tend to combine various halides, such as the anionic forms of bromine and iodine, with mixtures of methylammonium, formamidinium, cesium and other cations. These have led to record conversion efficiencies and thermal stabilities compared with their single-halide, single-cation analogs. However, these mixed-halide, mixed-cation perovskite films have been characterized only through ex-situ postdeposition techniques. This limits the understanding of the mechanisms that govern their growth from their sol-gel precursor to their solid state and stalls attempts to improve device performance and stability.

New method quantifies the efficiency of crystal semiconductors

Researchers at Tohoku University in Japan have found a new way to successfully detect the efficiency of crystal semiconductors. For the first time, the team used a specific kind of photoluminescence spectroscopy, a way to detect light, to characterize the semiconductors. The emitted light energy was used as an indicator of the crystal's quality. This method will potentially yield more efficient light-emitting diodes (LEDs), solar cells and several other advances in electronics.

Internal quantum efficiency of semiconducting crystals quantified by new method imageSchematic of the ARPL measurement technique

"For further development of perovskite-based devices, it is essential to quantitatively evaluate the absolute efficiency in high-quality perovskite crystals without assuming any predefined physical model is of particular importance," said corresponding author Kazunobu Kojima, Associate Professor at Tohoku University, Japan. "Our method is new and unique because previous methods have relied on efficiency estimation by model-dependent analyses of photoluminescence."

Mixing perovskite nanoparticles with 2D perovskites may give a boost to the efficiency of blue LEDs

Researchers from Zhejiang University, the Beijing Institute of Technology and Nanjing Tech University in China, Argonne National Laboratory in the U.S, University of Cambridge in the UK have combined perovskite nanoparticles with 2D perovskites to double the efficiency of blue LEDs.

Perovskite particle mix to push forward blue LEDs imageBromide perovskite films consisting of nanoparticles embedded within 2-D perovskite layers produce blue LEDs with a record-high efficiency of 9.5%

While the device only glows for a few minutes, the work is still considered “a big step toward the development of high-performance blue perovskite emitters” says Jianjun Tian of the University of Science and Technology in Beijing, who was not involved in the work. “The efficiency of these blue perovskite LEDs is already higher than that of the commercially available blue organic LEDs.”

German scientists use NiOx to increase efficiency of perovskite solar cells

Scientists at Germany's Karlsruhe Institute of Technology (KIT) and the Innovation Lab in Heidelberg have developed a highly efficient hole conductor layer made of nickel oxide (NiOx) that can be deposited over a large area and leads to record efficiencies in solar cells with organometallic perovskites.

KIT scientists improve the efficiency of PSCs with NiOx image

The team achieved efficiencies of up to 16.1% for completely vacuum-processed perovskite solar cells. With inkjet-printed absorber layers, the scientists achieved an efficiency record of up to 18.5%. "Currently, deposition by rotary coating, for which efficiencies of more than 24% have been achieved, dominates development. However, this can practically not be transferred to large areas" says Tobias Abzieher, PhD student at KIT's Light Technology Institute (LTI).

Researchers use perovskite absorbers to utilize infrared light in solar cells

Researchers from Florida State University and Georgia Tech have been working on new ways for solar cells to absorb and use infrared light, a portion of the solar spectrum that is typically unavailable for solar cell technology.

“We’re working on a process to optimize the efficiency of solar cells,” said Assistant Professor of Chemistry and Biochemistry Lea Nienhaus. “The main drive is to optimize this process for solar applications”. The team has created a new approach for solar cells to facilitate a process called photon upconversion. In photon upconversion, two low energy photons are converted into one high-energy photon that emits visible light.