Technical / research - Page 7

Solar cells and light-emitting diodes strive to maintain the excited state kinetics of molecules. A major loss mechanism, especially in the highest efficiency systems, is called exciton-exciton annihilation, leading to lowering of solar efficiency and of light output in LEDs. Controlling the amount of exciton-exciton annihilation is therefore an important goal that affects efficiency.

National Renewable Energy Laboratory (NREL) researchers, working with researchers from University of Colorado Boulder, sought to control exciton/exciton annihilation by coupling excitons with cavity polaritons, which are essentially photons caught between two mirrors, to combat energy dissipation and potentially increase efficiency in optoelectronic devices. As detailed in their recent article, the scientists used transient absorption spectroscopy to demonstrate control of the loss mechanism by varying the separation between the two mirrors forming the cavity enclosing the 2D perovskite (PEA)₂PbI₄ (PEPI) layer. This perovskite material is a candidate for future LED applications.

Researchers from China's Jinan University, University of Macau, Wuyi University, Guangdong Mellow Energy and Germany's IEK-5 Photovoltaik (Forschungszentrum Jülich) recently designed a two-terminal perovskite-silicon tandem solar cell that utilizes new hybrid interconnecting layers to reduce recombination losses in the top perovskite device. The tandem cell achieved an impressive fill factor of 81.8%, which the scientists said is the highest value ever reported for this cell technology to date.

The team's 2T perovskite-silicon tandem solar cell is based on special hybrid interconnecting layers (ICLs) that prevent direct contact between the perovskite absorber and transparent conductive oxide (TCO). The scientists' approach is based on sputtered nickel oxide (NiOx) as the seed layer of SAMs to build the hybrid interconnecting layers. The sputtered treatment technique provides, according to the team, an easy coating on a complex substrate and high reproducibility.

Researchers from NREL, Yale University, Hong Kong Baptist University and The Hong Kong University of Science and Technology (HKUST) have designed a chiral-structured interface in perovskite solar cells, which reportedly enhances their reliability and power conversion efficiency.

Using the PSC developed by the team to power a mobile phone as a demo. Image from Techxplore, credit HKUST

The performance of PSCs still faces significant barriers to commercialization, particularly due to various stability issues under real-world conditions. A major challenge is, according to the team, the insufficient adhesion between the different layers of the cells, resulting in limited interfacial reliability. To address this issue, the team was inspired by the mechanical strength of natural chiral materials and constructed an unprecedented chiral-structured interface in PSCs, unlocking very high reliability.

Researchers from the Chinese Academy of Sciences (CAS) posit that the efficiency and stability of perovskite modules are mainly limited by the quality of scalable perovskite films and sub-cells’ lateral contact. So, in their recent work, they addressed this by reporting constant low temperature substrates to regulate the growth of perovskite intermediate films to slow down the crystallization process. This is meant to assist in obtaining high-quality homogeneous perovskite films in large scale size, which avoid the effect of the ambient temperature on the film quality. 

Schematic diagram of the fabrication process of perovskite films using low-temperature substrate growth (LTSG). Image from Nature Communications

In addition, a scribing step named P1.5 was added before the top function layers deposition, so the diffusion barrier layer can be formed “naturally” at the interconnection interface without introducing any additional materials, which alleviates the diffusion degradation process. 

Researchers from Pakistan's University of Agriculture Faisalabad, University College of London United Kingdom and The National University of Malaysia have conducted a series of simulations to investigate how a cadmium telluride buffer layer (BL) may help increase efficiency and stability in perovskite solar cells. Their experiment showed that cell efficiency may climb from 11.09% to 23.56%.

Solar cell architecture with BL. Image credit: Results in Engineering

The researchers explained that the presence of a BL in a perovskite cell offers a porous structure that aids in forming the upper hole-transporting layer (HTL), while also preventing the leakage of corrosive additives from the HTL material. “The improvement in the development of HTM layer not only promotes efficient hole transfer and conduction but also restricts charge recombination,” they explained.

Integrating metal-halide perovskites with the industrially textured Czochralski silicon for perovskite/silicon tandem cells shows great promise for low-cost manufacturing and ideal light trapping. However, the conformal growth of high-quality perovskite film on fully textured silicon remains challenging due to the lack of effective regulation of structural evolution and residual strains. 

Recently, researchers from Nanchang University, Suzhou Maxwell Technologies, The Hong Kong Polytechnic University, CNPC Tubular Goods Research Institute, Henan Normal University, Southern University of Science and Technology, Chinese Academy of Sciences, City University of Hong Kong, Yunnan University, Harbin Institute of Technology (Shenzhen) and Fudan University reported a strain regulation strategy by forming a 3D/3D perovskite heterojunction at the buried interface through a vacuum-deposition method applicable to pyramidal texture. They found that the strained heterojunction enables high-performance, fully textured perovskite/silicon tandem solar cells that achieve an efficiency of up to 31.5%.

Researchers from King Abdullah University of Science and Technology (KAUST) and Marmara University set out to minimize crystal defects and film inhomogeneities in perovskite top cells, to achieve the full potential of monolithic perovskite/silicon tandem solar cells. 

In their recent work, the scientists discuss the use of methylenediammonium dichloride as an additive to the perovskite precursor solution, resulting in the incorporation of in situ–formed tetrahydrotriazinium (THTZ-H⁺) into the perovskite lattice upon film crystallization. 

Researchers from The Hong Kong University of Science and Technology, Oxford University and the University of Sheffield have developed a molecular treatment that significantly enhances the efficiency and durability of perovskite solar cells. 

A key to the solution was their successful identification of critical parameters that determine the performance and lifespan of halide perovskites. The research team investigated various ways of passivation, a chemical process that reduces the number of defects or mitigates their impact in materials, thereby enhancing the performance and longevity of devices comprising these materials. They focused on the “amino-silane” molecular family for passivating perovskite solar cells.

Researchers from Chung-Ang University, Gwangju Institute of Science and Technology, Hanyang University, The University of Electro-Communications and Chungbuk National University have reported that introducing 4-Phenylthiosemicarbazide (4PTSC) as an additive during the production of tin halide perovskites (Sn-HPs) can boost the performance of perovskite solar cells (PSCs).

Through extensive analyses and experimental comparisons between regular Sn-HP PSCs and those containing the proposed additive, the researchers showcased the multiple functionalities of 4PTSC as an additive. "We purposely chose a multifunctional molecule that acts as a coordination complex and a reducing agent, passivates defect formation, and improves stability," explains Associate Professor Dong-Won Kang from Chung-Ang University, who led the study.

Researchers from Nanjing University of Aeronautics and Astronautics in China and the UK's University of Cambridge have reported a scalable stabilization method using vapor-phase fluoride treatment, which achieved 18.1%-efficient perovskite solar modules (228 square centimeters) with accelerated aging–projected T80 lifetimes (time to 80% of efficiency remaining) of 43,000 ± 9000 hours under 1-sun illumination at 30°C. 

The high stability results from vapor-enabled homogeneous fluorine passivation over large-area perovskite surfaces, suppressing defect formation energy and ion diffusion. The extracted degradation activation energy of 0.61 electron volts for solar modules is comparable to that of most reported stable cells, which indicates that modules are not inherently less stable than cells and closes the cell-to-module stability gap.