Efficiency - Page 49

Researchers at the University of Rome Tor Vergata in Italy and Russia's NUST MISIS institute have investigated how cells containing two-dimensional titanium-carbide MXene support layers could improve perovskite solar cell performance.

To obtain good power conversion within a perovskite solar cell, all layers and layer interfaces within the cell must have good compatibility. Typical cells contain the active perovskite material sandwiched between two charge transport layers, which are then adjacent to their corresponding electrodes. Support layers may also be added. Charge mobility, energy barriers, interface energy alignment, and interfacial vacancies all impact compatibility and subsequent cell performance and stability. Thus, engineering well-suited interfaces with the cell is paramount to cell success and long-term stability, an important criterion for potential commercialization.

Researchers from the Ulsan Institute of Science and Technology (UNIST) have demonstrated a new method of fabricating perovskite-on-silicon tandem devices, using a transparent conductive adhesive (TCA) to combine the two cells. The scientists have developed devices with demonstrated efficiencies of 19.4%, and propose methods to bring that up to over 24% using existing technology.

While the efficiency is still well below the 28% record for a perovskite/silicon tandem cell set by Oxford PV, the UNIST group says its method is far simpler to manufacture than previous concepts. 'It is meaningful to develop an attached tandem solar cell unlike the conventional tandem solar cell with stacked structure,' said UNIST's In Young Choi, lead author of the study. 'We have observed that the TCA effectively connects the different light-absorbing layers.'

A team led by Prof. Steve Albrecht from the HZB has announced a new world-record: a tandem solar cell with certified efficiency of 23.26% that combines the semiconducting materials perovskite and CIGS. One reason for this success lies in the cell's intermediate layer of organic molecules: they self-organize to cover even rough semiconductor surfaces. Two patents have been filed for these layers.

Perovskite-based solar cells have experienced an incredibly rapid increase in efficiency over the last ten years. The combination of perovskites with classical semiconductor materials such as silicon and copper-indium-gallium-selenide (CIGS) compounds in tandem solar cells promises low-cost, high-performance solar modules for the future. However, losses at the electrodes between the two semiconductors considerably reduce the efficiency.

Solliance and U.S-based MiaSolé announced a new record - power conversion efficiency of 23% on a flexible tandem solar cell: a top flexible semi-transparent perovskite solar cell with a bottom flexible copper indium gallium selenide (CIGS) cell.

This achievement comes only 9 months after the January 2019 announcement by Solliance and MiaSolé regarding a flexible solar cell with an impressive power conversion efficiency of 21.5%. The solar cell, similarly to this newly announced one, combined 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.

German university the Karlsruhe Institute of Technology (KIT), the Center for Solar Energy and Hydrogen Research Baden-Würtetemburg (ZSW) and CIGS module manufacturer Nice Solar Energy have announced an ambition to design tandem PV modules based on CIGS and perovskite, which can theoretically achieve efficiencies well above 30%.

The joint 'Capitano' project will run for three years and has received more than €5 million from Germany's Federal Ministry for Economic Affairs and Energy. The aim of the project is to develop cells with stable higher efficiencies, which can be interconnected to form efficient tandem solar modules.

Researchers from the Australian National University (ANU) have reportedly broken new ground in solar cell energy efficiency and in the process provided a glimpse of the technology's future. The researchers have a announced a record of 21.6% efficiency, which they say is the highest achieved for perovskite cells above a certain size.

Associate Professor Thomas White says as a comparison, typical solar panels being installed on rooftops right now have efficiencies of 17-18%. 'There are three things you're trying to achieve with solar cells, you're trying to make them efficient, stable and cheap," he said. "Perovskites are the future of 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 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.

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.

Schematic 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."

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.

Bromide 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.'

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.

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).