The potential of solar cells to tackle energy and environmental challenges by replacing traditional fossil fuels is gaining more recognition and support globally. However, the current photoelectric conversion efficiency of solar cells remains relatively low. Three main factors limit this efficiency: light absorption, separation and transport of photogenerated electron-hole pairs, and charge collection.
Photovoltaic materials play a crucial role in determining the performance of solar cells. Therefore, the primary approach to improving efficiency lies in enhancing light absorption and minimizing carrier recombination. Research in these areas focuses heavily on manipulating the material’s energy band structure. Developing new photovoltaic materials with optimal band alignment remains a challenging and highly active area of research.
Recently, a research team led by Professor Huang Fuqiang from the Shanghai Institute of Ceramics, Chinese Academy of Sciences, and Peking University's Department of Chemistry, introduced a novel strategy. They incorporated tin (Sn) into the In/Ga sites of chalcopyrite-based materials such as CuInSâ‚‚ and CuGaSâ‚‚. This process successfully created a half-filled intermediate band within the bandgap. For example, Sn-doped CuGaSâ‚‚ reduced its bandgap to 1.8 eV, extending the absorption range into the near-infrared region (down to 1.0 eV). Similarly, Sn-doped CuInSâ‚‚ thin films showed a bandgap reduction as low as 1.0 eV. This intermediate band acts as a bridge for low-energy photon transitions, overcoming the limitations imposed by the optical bandgap and enabling three excitation channels: VBM-CBM, VBM-IB, and IB-CBM. As a result, the material covers a much broader portion of the solar spectrum, significantly increasing photocurrent and potentially boosting the overall conversion efficiency.
In addition, the team explored a new type of narrow-bandgap ferroelectric photovoltaic material called KBiFe₂O₅. By adjusting the coordination field around the central ions, they managed to reduce the bandgap effectively. The material has a unique three-dimensional framework structure, composed of FeO₄ tetrahedra connected by Bi₂O₂ chains. With a bandgap of 1.59 eV, it represents the narrowest bandgap among known high-temperature multiferroic materials. Due to the intrinsic polarization field, the recombination of photogenerated carriers is suppressed, leading to a strong photovoltaic response. The sample achieved a remarkable open-circuit voltage of 8.8 V and a photocurrent density of 15 mA/cm²—significantly surpassing existing ferroelectric photovoltaic materials.
This research marks an important step forward in the development of next-generation solar cells. It not only introduces a new intermediate-band material with broad spectral response and enhanced photocurrent but also demonstrates how structural design can be used to control the bandgap in ferroelectric photovoltaics. These findings offer fresh insights into creating high-efficiency solar cells with precisely engineered microstructures.
The study was supported by several key programs, including the National Natural Science Foundation of China, the National 863 Program, and the Innovation Project of the Chinese Academy of Sciences. The results 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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