Technical / research

Researchers from Spain's UPV/EHU, ICIQ-BIST, CIDETEC and Mexico's Instituto Politécnico Nacional have explored the effect of chalcogen substitutions in fullerene derivatives to enhance efficiency and stability of perovskite solar cells.

The team examined the effects of chalcogen substitution in the chemical structure of phenyl-butyric acid methyl ester (PCBM) on the performance and stability of inverted perovskite solar cells (PSCs). PCBMs are the most widely used electron transport materials in inverted PSCs. However, these compounds can suffer from lack of stability under irradiation. In the race for optimizing the PCBM-like derivatives, the thiophene moiety has garnered significant attention for enhancing the performance and stability of PSCs. The novelty in this study relies on the tests done on the selenophene derivative. This compound was compared to thiophene and furan substituted derivatives, and to the reference PCBM without a chalcogenophene moiety, demonstrating a better surface passivation and reduced interfacial charge recombination.

Carbon-based all-inorganic perovskite solar cells (C-PSCs) are known for their inexpensive manufacturing process. However, their perovskite constituents are susceptible to the formation of numerous structural defects and halide vacancies, which can induce substantial energy level misalignments between the light-absorbing layer and the carbon electrode. This discrepancy hinders the extraction and transfer of holes, thereby adversely affecting the overall efficiency of the device. 

Image credit: Chemical Engineering Journal

Researchers from China's Huaqiao University have proposed an interfacial post-treatment strategy aimed at reinforcing perovskite layers through the application of Neostigmine bromide (NMB) as a modifier. The team employed NMB to treat the upper interface of the perovskite, addressing intrinsic phase segregation, passivating surface defects, and filling halogen vacancies, thereby enhancing the photoelectric performance and stability of the device.

Aiming to explore the potential of sulfur-based additives for increasing both device power conversion efficiency and moisture stability of perovskite solar cells, researchers from BCMaterials (Spain), Huazhong University of Science and Technology (China), Max Planck Institute for Polymer Research (Germany) and CNRS (France) have reported a mechanism for the local nanoscopic humidity ingression into a multifunctional additiviated formamidinium-loaded halide perovskites.

a) The molecular structure of additives used. Image from: Advanced Energy Materials

By tuning the iodide and bromide tails of the additives, the influence of sulfur heteroatom containing ammonium-amidinium salts on the photo-physical and device properties of a formamidinium-rich perovskite absorber was uncovered. 

Researchers from China's Jiangxi Normal University, Chinese Academy of Sciences (CAS) and City University of Hong Kong have developed a self-driven X-ray detection device using high resistivity zero-dimensional lead-free perovskite ferroelectric single-crystal (NMP)₃Sb₂Br₉. The device exhibits an excellent self-driven X-ray detection performance, with an ultra-low detection limit of 84.1 nGyair/s, approximately 60 times lower than that of commercial α-Se (5500 nGyair/s).

The self-driven detection mode without external bias has been proven to be an effective means of reducing the limit of detection (LoD) due to its low current noise characteristics. Additionally, the zero-dimensional distinctive isolated framework results in a high resistivity of 1.39 × 1011 W cm, which effectively reduces the current noise and suppresses ion migration. 

Researchers from the Chinese Academy of Sciences (CAS), ShanghaiTech University, Zhejiang Laboratory and Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering recently reported an efficient (>27% reported efficiency) perovskite solar cell that uses a back mirror based on silver to improve light harvesting. 

The ultrathin perovskite solar cell utilizes a Gires-Tournois resonator to improve light absorption - an optical standing-wave resonator designed for generating chromatic dispersion. Gires-Tournois resonators are usually based on a reflective metal mirror and are primarily used in chirping applications such as pulse compression. The structure of the resonator in this study had a simple optical structure, combined with a silver back mirror, to optimize light capture and utilization while improving light absorption capacity.

Researchers from Northwestern University, University of Toronto and Griffith University have developed a new protective coating that significantly extends the life of perovskite solar cells, making them more practical for real-world applications.

Typically, perovskite solar cells use an ammonium-based coating layer to enhance efficiency. While effective, ammonium-based layers degrade under environmental stress, including heat and moisture. The team has now developed a more robust layer — based on amidinium. In experiments, the new coating was 10 times more resistant to decomposition compared to conventional ammonium-based coatings. In addition, the amidinium-coated cells also tripled the cell’s T90 lifetime — the time it takes for a cell’s efficiency to drop 90% of its initial value when exposed to harsh conditions.

Researchers from the University of Oxford, University of Manchester,  University of Sheffield and Helmholtz-Zentrum Berlin (HZB) have developed a high volatility, low toxicity, biorenewable solvent system to fabricate a range of 2D perovskites, which can be used as effective precursor phases for subsequent transformation to α-formamidinium lead triiodide (α-FAPbI₃), fully processed under ambient conditions. 

This solvent system is meant to address challenges involved with producing perovskite solar cells (PSCs) via high-throughput coating methods, such as the use of harmful solvents, the expense of maintaining controlled atmospheric conditions, and the inherent instabilities of PSCs under operation. 

Researchers from Nanyang Technological University (NTU) and The Hong Kong Polytechnic University, led by Associate Professor Nripan Mathews of NTU’s School of Materials Science and Engineering, have synthesized four unique types of 2D halide perovskites.

Dr. Ayan Zhumekenov, a research fellow at the school and lead author of the study, used a novel approach to create the new perovskites by incorporating dimethyl carbonate – a non-toxic solvent – into methylammonium-based perovskite crystals. By analyzing the new crystal structures, the scientists discovered that the structures’ band gap could be tuned by adjusting the ratio of methylammonium to dimethyl carbonate in them. The band gap, which determines 
the color of the material, is the energy required for an electron to break free from its bound state and become conductive.

Researchers from King Abdullah University of Science and Technology (KAUST), the University of Manchester and Marvell Semiconductor have developed an innovative high-speed photodetector design utilizing ultrathin two-dimensional metal halide perovskites (2D-MHP), coupled with a planar nanocavity to significantly enhance optical absorptance—achieving more than a fourfold increase in a solution-processed 10-nm-thick 2D-MHP film. 

This integration facilitates an exceptional response time (30 ns) alongside a high responsivity of 2.12 A W⁻¹. The method is said to overcome traditional constraints related to thickness and absorption, thereby optimizing device speed and dark noise features through active area variation.

The fabrication of perovskite/Si tandem solar cells often encounters the challenge of selecting a suitable sputtering buffer layer (SBL) to prevent damage during the transparent electrode deposition. In their recent work, researchers from China's Northwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene (NPU), Chinese Academy of Sciences and Ningbo New Materials Testing and Evaluation Center Co. developed a perovskite-silicon tandem solar cell that uses an indium oxide sputtering buffer layer to protect the perovskite absorber and the electron transport layer from damages that might occur during the electrode deposition process. The new layer not only granted this protection but also showed strong optical and electrical properties. 

The team introduced the indium oxide (In₂O₃) buffer layer via e-beam deposition to fabricate semi-transparent perovskite solar cells. The optical transmittance and electrical conductivity of In₂O₃ highly depend on the deposition rate. High deposition rate results in high ratio of metallic indium in the film, which causes severe parasitic absorption. A 20 nm-thick In₂O₃ film deposited at lower rate demonstrated high conductivity, transmittance and robust protection during sputtering.