A new semiconductor nanofiber could significantly increase the efficiency of solar cells

A team from the Polytechnic University of Hong Kong (PolyU) has developed a new nanostructure integrated with a semiconductor nanofiber offering exceptional conductivity. Nanocomposite is a key inhibitor of conductivity that can improve a wide range of applications, from batteries to solar cells, to air purification devices.

Although semiconductors are widely used, their efficiency has been limited by the natural process of photo-generated electrons by recombining with "holes", or potential resting points for electrons. This reduces the moving current of electrons generated by the light or external power supply and, therefore, reduces the efficiency of the device. PolyU's mechanical engineering department has designed a composite nanofiber that essentially provides a super-dedicated highway for electron transport once they are generated, thus eliminating the problem of electron-hole recombination.

The innovation received the gold medal with congratulations from the jury at the 45th International Exhibition of Inventions of Geneva in 2017.

The team avoided recombination by inserting a highly conductive nanostructure composed of carbon nanotubes and graphene into a titanium dioxide (TiO 2).₂) composite nanofiber. Electrons and charges can be transported efficiently into the graphene nucleus as soon as they are generated, before recombining with the "holes" of the nanofiber. Under the direction of Wallace Leung, the team tested the effectiveness of nanocomposite in solar cells and photocatalysts for air purification.

They integrated the nanocomposite into the TiO₂ component of dye sensitized and perovskite-based solar cells, which are being studied as alternatives to conventional silicon-based solar cells. Nanocomposite has increased energy conversion rates of solar cells by 40 to 66%.

TiO₂ Nanoparticles are the most commonly used photocatalyst material in commercially available air purifying or disinfecting devices. However, TiO₂ can only be activated by ultraviolet light, which makes it much less effective inside. It is also inefficient to convert nitric oxide (NO) to nitrogen dioxide (NO₂), at a rate of less than 10%.

When the PolyU nanostructure was incorporated into a photocatalyst, it provided a fast graphene pathway that allowed electrons to move faster to generate super anions to oxidize pollutants, bacteria, and viruses that were absorbed. The graphene core also dramatically increased the area exposed to light absorption and trapping of harmful molecules. It also collected more light energy at all wavelengths. The semiconductor nanofiber has converted about 70% of NO to NO₂, seven times more than a simple TiO₂ nanoparticles.

They also tested the ability of their nanostructure to break down formaldehyde, an uncomfortable volatile organic compound that is commonly found in new or renovated buildings and in new cars. PolyU's embedded graphene photocatalyst has once again been able to break down three times more formaldehyde than TiO₂ nanoparticles without the added nanostructure.

The new nanocomposite has a wide range of potential applications, such as water-splitting hydrogen generation, enhanced speed and sensitivity biochemical sensors, and reduced impedance and increased storage lithium batteries.

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