Technical / research - Page 33

Researchers from Russia's Alferov University, ITMO University, Far Eastern Branch of Russian Academy of Sciences, Peter the Great St. Petersburg Polytechnic University, Skolkovo Institute of Science and Technology and China's Qingdao Innovation and Development Center have developed a novel design for a perovskite electrochemical cell for light-emission and light-detection, where the active layer consists of a composite material made of halide perovskite microcrystals, polymer support matrix, and added mobile ions.

Schematic diagrams of (a) the typical PeLED device structure, where CTL - charge transfer layer, QD - quantum dots and (b) the team's PeLEC device structure, where SWCNT - single-walled carbon nanotubes. Image from Opto-Electronic Advances.

The team explained that while halide perovskite light-emitting devices exhibit exceptional properties such as high efficiency, high color purity, and broad color gamut, their industrial integration generally suffers from the technological complexity of devices' multilayer structure alongside in-operation induced heating poor stability. Halide perovskite light-emitting electrochemical cells are a novel type of perovskite optoelectronic device that differs from the perovskite light-emitting diodes by a simple monolayered architecture. 

A team of researchers at MIT, Complutense University of Madrid and the University of Pavia has designed a perovskite-based device that combines aspects of electronics and photonics, that could lead to new kinds of computer chips or quantum qubits.

The new work involved sandwiching tiny flakes of a perovskite material in between two precisely spaced reflective surfaces. By creating these perovskite sandwiches and stimulating them with laser beams, the researchers were able to directly control the momentum of certain “quasiparticles” within the system. Known as exciton-polariton pairs, these quasiparticles are hybrids of light and matter. Being able to control this property could ultimately make it possible to read and write data to devices based on this phenomenon.

A research team from City University of Hong Kong (CityU) and University of Washington recently developed a multifunctional and non-volatile additive which can improve the efficiency and stability of perovskite solar cells (PSCs) by modulating perovskite film growth. 

The team explained that the additive can be used to modulate the kinetics of perovskite film growth through a hydrogen-bond-bridged intermediate phase. The additive enables the formation of large perovskite grains and coherent grain growth from bottom to the surface of the film. The enhanced film morphology reportedly results in significantly reduced non-radiative recombinations, thus boosting the power conversion efficiency of inverted (p–i–n) solar cells to 24.8% (24.5% certified) with a low energy loss of 0.36 eV. The unencapsulated devices exhibited improved thermal stability with a T98 lifetime beyond 1,000 h under continuous heating at 65 ± 5 °C in a nitrogen-filled glovebox. This effective approach can also be applied to wide-bandgap perovskites and large-area devices to show reduced voltage loss and high efficiency.

Researchers from China's Chongqing University, the Chinese Academy of Sciences (CAS) and JA Solar Holdings Co., along with South Korea's Ulsan National Institute of Science and Technology (UNIST) and Germany's CTF Solar and have designed a perovskite solar cell based on a binary mixed hole transport layer (HTL) that reportedly offers better performance than HTLs that rely on commonly utilized hygroscopic dopants.

The team mixed two popular hole transport materials to form a binary mixed HTL, that exhibited improved moisture resistance. As a result, PSCs equipped with the mixed HTL achieved a champion power conversion efficiency (PCE) of up to 24.3% and superior operational stability. The cells without encapsulation can maintain 90% initial efficiency after storage in dark ambient conditions (30% RH) for 1200 hours. These results suggest that such a mixed HTL could be a promising strategy to meet the future photovoltaic applications demands with low-cost as well as excellent efficiency and device stability.

Researchers at Nanjing University, Nankai University, East China Normal University and University of Toronto have developed new inorganic wide-bandgap perovskite subcells that could increase the efficiency and stability of all-perovskite tandem solar cells. Their design involves the insertion of a passivating dipole layer at the interface between organic transport layers and inorganic perovskites within the cells.

The scientists explained that efficient tandem solar cells made using hybrid organic inorganic wide-bandgap perovskites have thus far maintained only 90% of their initial PCE for 600 hours of operation at their maximum power point (MPP). Therefore, achieving long-term stability has become a critical issue for the commercialization of all-perovskite tandem solar cells.

Researchers at the Indian Institute of Technology Bombay have reported NIR-transparent perovskite solar cells (PSCs) with the stable triple cation perovskite as the photo-absorber and subsequent integration with a Si solar cell in a 4T tandem device. The scientists said that the cell provides outstanding stability in the dark, as well as continuous heating conditions.

The top perovskite cell incorporates a room-temperature sputtered transparent conducting electrode (TCE) as a rear electrode. It has an n–i–p structure and utilizes an anti-reflecting coating, an electron transport layer (ETL) made of tin(IV) oxide (SnO₂), a perovskite layer, a molybdenum oxide (MoOx) layer, and a spiro-OMeTAD hole transport layer (HTL). The MoOx buffer layer protects the perovskite photo-absorber and charge transport layers from any sputter damage.

Researchers from East China University of Science and Technology, Jilin University, Huazhong University of Science and Technology, ShanghaiTech University, Chinese Academy of Sciences, Shanghai Jiao Tong University and University of Potsdam have found that a new molecular hole-transporter can improve the performance of inverted perovskite solar cells and mini modules.

Left: mini module. Upper right: contact angle of the perovskite solution on the self assembled monolayer. Lower right: PL emission of a perovskite film. Image from University of Potsdam website.

Inverted perovskite solar cells are seen as particularly promising thanks to their simple fabrication at low costs and their relative stability. Inverted perovskite solar cells resemble organic solar cells, with a layer of perovskite replacing the organic absorber layer. In the recent study, the authors developed a novel hole transport layer based on a self-assembled monolayer. This monolayer consists of amphiphilic molecules, molecules that are both hydrophilic (water-soluble) and hydrophobic (water-fearing). 

Researchers from the University of Surrey, University of Toronto, University of Stuttgart and Ulsan National Institute of Science and Technology have found that stabilizing the perovskite "photoactive phases" – the specific part of the material that is responsible for converting light energy into electrical energy – is the key step towards extending the lifespan of perovskite solar cells. The stability of the photoactive phase is important because if it degrades or breaks down over time, the solar cell will not be able to generate electricity efficiently. Therefore, stabilizing the photoactive phase is a critical step in improving the longevity and effectiveness of perovskite solar cells.

In the study, the team assessed the current understanding of these phase instabilities and summarized the approaches for stabilizing the desired phases, covering aspects from fundamental research to device engineering. The scientists subsequently analyzed the remaining challenges for perovskite PVs and demonstrated the opportunities to enhance phase stability with ongoing materials discovery and in operando analysis. Finally, the team proposed future directions towards upscaling perovskite modules, multijunction PVs and other potential applications.

An international research team that includes scientists from EPFL in Switzerland, Middle East Technical University (METU) in Turkey, Lomonosov Moscow State University in Russia and The University of Tokyo has fabricated a quasi-2D perovskite solar cell with a unique type of salt to enhance hole extraction. 

The triple-cation perovskite absorber was treated with phenethylammonium iodide (PEAI), a modulator that alters the perovskite film's surface energy and forms a quasi-2D structure without further annealing. The result is a 23.08%-efficient device that is also able to retain 95% of its initial efficiency after 900 hours.

Researchers at the Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences (CAS), University of Macau and Celanese (China) Holding have developed a long-alkyl- chain anionic surfactant (LAS) additive that can significantly improve the long-term operational stability of perovskite/silicon tandem solar cells.

Traditional methods to improve the stability of perovskite solar cells include encapsulation, crystallization engineering, and defect passivation. Similar to “stress corrosion” in metals, glass and polymers, subcritical perovskite deterioration inevitably occurs due to tensile stress during the fabrication and operation, which degrades device performance. To suppress the “stress corrosion”, the researchers developed the novel LAS additive for the perovskite/silicon tandem solar cells.