Efficiency - Page 53

Researchers at Helmholtz-Zentrum Berlin (HZB) have demonstrated 25.5% efficiency for monolithic perovskite/silicon tandem solar cells using textured foil. In addition, the impact of texture position on performance and energy yield is simulated in their new work.

Tandem solar cell device schematics of the experimentally realized architecture and SEM cross section image of the top cell

The research team used a textured light management (LM) foil on the front-side of a tandem solar cell processed on a wafer with planar front-side and textured back-side. Consequently, the PCE of monolithic, 2-terminal perovskite/silicon-heterojunction tandem solar cells was improved from 23.4% to 25.5%. This approach replaced the use of textured silicon wafers, that can be utilized for light management but are typically not compatible with perovskite solution processing.

Two papers have recently been published, reporting on perovskite-based LEDs. The efficiencies with which some perovskite LEDs (PLEDs) produce light from electrons already seem to rival those of OLEDs.

Both papers, by Cao et al. and Lin et al., have developed PLEDs that break an important technological barrier: the external quantum efficiency (EQE) of the devices, which quantifies the number of photons produced per electron consumed, is greater than 20%. There are several similarities between the devices reported by the two groups. Perhaps most notably, the active (emissive) perovskite layer is about 200 nanometres thick in both cases, and is sandwiched between two relatively simple electrodes. This design is called a planar structure, and is the most basic manifestation of diodes made from thin films of materials. The electrodes are appropriately modified to ensure that electrons and holes (quasiparticles formed by the absence of electrons in atomic lattices) are efficiently pumped into the perovskite. As in all LEDs, when electrons meet holes, they can release energy in the form of photons through a process known as radiative recombination.

Researchers at the Adolphe Merkle Institute in Fribourg and the Ecole Polytechnique Fédérale de Lausanne have developed a new technique to replace one of the least stable components in perovskite solar cells, which could be a major step towards commercialization.

Perovskites are seen as promising thin-film solar-cell materials because they can absorb light over a broad range of solar spectrum wavelengths thanks to their tuneable bandgaps. Charge carriers (electrons and holes) can also diffuse through them quickly and over long lengths. The most efficient perovskite solar cells usually contain bromide and MA, which is thermally unstable. To overcome this problem, researchers tried replace MA with FA since it is not only more thermally stable but also has an optimal redshifted bandgap. Unfortunately, because of its large size, FA does distort the perovskite lattice and tends to produce a photoinactive 'yellow' phase at room temperature. The other photoactive 'black phase' can only be seen at high temperatures. However, the researchers in this new work have now found a way to stabilize the black phase of FA at room temperature.

Swansea University researchers have declared a perovskite solar module the size of an A4 sheet of paper, (nearly six times bigger than 10x10 cm² modules of that type reported before), developed by using simple and low-cost printing techniques. The accomplishment shows that the technology works at a larger scale, not just in the lab, which is crucial for commercial use.

The team works for the SPECIFIC Innovation and Knowledge Center led by Swansea University. The researchers used an existing type of cell, a Carbon Perovskite Solar Cell (C-PSC), made of different layers - titania, zirconia and carbon on top - which are all printable. Though their efficiency is lower than other perovskite cell types, C-PSCs do not degrade as quickly, which has been established through 1 year of stable operation under illumination.

Researchers at Penn State have gained new insight into how halide perovskite materials enable the efficient conversion of sunlight into electricity.

Scientists state that halide perovskites tend to have a unique tolerance for imperfections in their structures, which allows them to efficiently convert sunlight into electricity when other materials with similar imperfections do not. What makes these materials so tolerant of imperfections, however, was unknown prior to this study. The researchers used ultrafast infrared imaging technology to investigate how the structure and composition of these materials influence their ability to convert sunlight into electricity.

Researchers at the Energy Materials and Surface Sciences Unit at the Okinawa Institute of Science and Technology Graduate University (OIST) have designed a new method to fabricate low-cost high-efficiency solar cells. Prof. Yabing Qi and his team from OIST, in collaboration with Prof. Shengzhong Liu from Shaanxi Normal University, China, developed the cells using perovskite materials.

In what Prof. Qi defines as "the golden triangle," solar cell technologies need to fulfill three conditions to be worth commercializing: their conversion rate of sunlight into electricity must be high, they must be inexpensive to produce, and they must have a long lifespan. Today, most commercial solar cells are made from crystalline silicon, which has a relatively high efficiency of around 22%. Though silicon, the raw material for these solar cells, is abundant, processing it tends to be complex and shoots up the manufacturing costs, making the finished product expensive.

Researchers from the Chinese Academy of Sciences have designed perovskite solar cells with power conversion efficiency of 18.1% by adding Titanium (Ti) cathode layer.

Two different device configurations including n-i-p and p-i-n have been adopted for fabricating the PSCs. As organic electron transport layers (ETLs), fullerene and its derivatives (C60 and PCBM) play an important role in efficient PSCs with p-i-n structure (ITO/Hole transport layers/perovskite/ETLs/Cathode). However, the cathode metal atoms diffuse through the organic ETLs to the perovskite layer, causing degradation of PSCs. Also, the instability and high-cost of organic ETLs were limiting factors for the commercialization of PSCs. Considering these problems, the research team led by Dr. LI Xinhua, developed the ultra-thin Ti cathode interlayer to replace organic ETLs for fabricating efficient and low-cost PSCs.

The Engineering and Physical Sciences Research Council (EPSRC) has announced seven new Prosperity Partnership projects that will build links between the UK's research base and leading industry partners. The new projects will focus on four of the Industrial Strategy Grand Challenges (ISCF) , involve nineteen industry partners and ten universities, and will fund 50 studentships.

Prosperity Partnerships are EPSRC's flagship approach to co-investing with business in long-term, use-inspired, basic research. They are five-year, multi-million pound research collaborations on topics of national and global importance which have been co-created by leading UK universities and businesses with a strong research presence in the UK.

imec, the world-leading research and innovation hub, recently presented an impressive thin-film tandem solar cell at the EU PVSEC conference. The cell consists of a top perovskite cell developed by imec within the partnerships of EnergyVille and Solliance, and a bottom CIGS cell from the Centre for Solar Energy and Hydrogen Research (ZSW, Stuttgart, Germany). The tandem cell resulting from this collaboration achieves a record efficiency of 24.6%.

The perovskite top cell in the tandem uses light in the visible part of the solar spectrum, while the light in the near-IR spectrum that passes through the perovskite cell is harvested by the underlying CIGS cell. In this way, the tandem cell significantly outperforms the stand-alone perovskite and CIGS cells. Moreover, both perovskite and CIGS cells are thin-film solar cells, paving the way to high efficiency flexible solar cells and building integrated photovoltaic (BIPV) solutions.

Researchers from Qatar, Switzerland and Italy have designed a composite perovskite material with a thin surface layer that repels water and protects against moisture-induced degradation. The team has managed to do this by allowing the self-assembly of two-dimensional perovskite on top of a three-dimensional perovskite in an inert atmosphere.

The composite perovskite did not decompose when kept in highly humid air for three days. The top layer of the 2D perovskite blocked water penetration into the 3D perovskite beneath it, preventing its degradation. Bare 3D perovskite completely degrades at a similar humidity.