The growing recognition of solar cells as a viable solution to energy and environmental challenges has sparked global interest in replacing fossil fuels with renewable energy sources. However, the current photoelectric conversion efficiency of solar cells remains relatively low. Three key factors limit this efficiency: light absorption, the separation and transport of photogenerated electron-hole pairs, and the collection of charges. To enhance performance, researchers focus on improving light absorption and reducing carrier recombination, both of which are closely tied to the material's energy band structure.
Photovoltaic materials play a central role in solar cell performance. Thus, the primary approach to boosting efficiency is to optimize light absorption and suppress carrier recombination. Recent advancements have focused on modifying the energy bands of these materials. Creating new photovoltaic materials with precise band alignment remains a major challenge and a hot topic in research.
A research team led by Dr. Huang Fuqiang from the Shanghai Institute of Ceramics, Chinese Academy of Sciences, and Peking University’s Department of Chemistry has made significant progress. They introduced tin (Sn) into the In/Ga sites of chalcopyrite materials such as CuInS₂ and CuGaS₂. This innovative approach successfully created a half-filled intermediate band within the bandgap. For example, Sn-doped CuGaS₂ reduced its band gap to 1.8 eV, extending light absorption into the near-infrared region (down to 1.0 eV). Similarly, Sn-doped CuInS₂ thin films achieved a band gap as low as 1.0 eV. This intermediate band serves as a bridge for low-energy photons, broadening the solar spectrum response and enabling three distinct excitation channels: valence band to conduction band, valence band to intermediate band, and intermediate band to conduction band. As a result, the photocurrent significantly increases, offering great potential for enhancing solar cell efficiency.
Another breakthrough came from the development of a novel narrow-bandgap ferroelectric photovoltaic material: KBiFe₂O₅. By manipulating the ion coordination field, the research team successfully narrowed the bandgap to 1.59 eV, making it the smallest bandgap among known high-temperature multiferroic materials. The material features a three-dimensional framework structure with FeO₄ tetrahedra connected by Bi₂O₂ chains. Due to its intrinsic polarization field, the recombination of photogenerated carriers is effectively suppressed. This leads to a strong photovoltaic response, with an open-circuit voltage reaching 8.8 V and a photocurrent density of 15 mA/cm²—exceeding the performance of existing ferroelectric photovoltaic materials.
This research marks a significant step forward. On one hand, it introduces a new intermediate-band solar cell material that achieves wide spectral response and enhanced photocurrent. On the other hand, it demonstrates effective control over the bandgap in ferroelectric photovoltaics, offering new insights for developing next-generation solar cells with improved efficiency and controllable microstructures.
The study was supported by several funding bodies, including the National Natural Science Foundation of China, the National 863 Program, and the Chinese Academy of Sciences' Innovation and Class B Pilot Projects. The findings were published in *Nature Scientific Reports* in 2013 (Vol. 3, pp. 1265; Vol. 3, pp. 1286).
Toilet Tank
A toilet tank, also known as a hidden cistern, is a modern plumbing fixture used in bathrooms and toilets. It is designed to hide the flushing mechanism behind a wall or inside a piece of furniture, providing a sleek and minimalist look to the bathroom space.
The main purpose of a concealed flush tank is to save space and create a clean aesthetic by concealing the unsightly plumbing components typically associated with traditional exposed cisterns. By integrating the flush tank within the wall or furniture, only the flush buttons or plates are visible to the user.
Concealed cisterns come in various designs and sizes to accommodate different installation requirements. They are usually made of durable materials such as ABS plastic or stainless steel to ensure longevity and resistance to water damage. The tanks are equipped with a water inlet valve, a flushing mechanism, and an outlet pipe connected to the toilet bowl.
In addition to the aesthetic benefits, installation systems also offer practical advantages. They are typically equipped with dual-flush mechanisms, allowing users to choose between a full flush for solid waste and a partial flush for liquid waste. This dual-flush feature helps in conserving water by reducing the amount used for each flush, contributing to water efficiency and environmental sustainability.
Installation of a concealed cistern requires professional plumbing expertise, as it involves cutting into the wall and connecting the tank to the toilet bowl. However, once properly installed, the maintenance and upkeep of a concealed toilet tank are relatively straightforward.
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