Hybrids and related materials - Page 8

A team of researchers from Italy has created hybrid perovskite-graphene solar cells that show good stability upon exposure to sunlight, while still maintaining an impressive efficiency of over 18% - the highest reported efficiency of graphene perovskite hybrid solar cells to date.

Despite tremendous progress in Perovskite PV performance, the stability of these devices is still questionable. In particular, air and humidity degrade cell performance, as do continued exposure to sunlight and heat, setting back the advantages over other types of solar cells. Graphene and graphene-related materials (GRMs) have properties that make them shine in applications like protective layers, andso arise as natural candidates to protect PSCs from atmospheric degradation.

Researchers from Karlsruhe Institute of Technology (KIT), ZSW and IMEC presented at the PSCO international conference a prototype of the new solar module using thin-film technology. According to the researchers, an efficiency of 17.8% has been achieved in this prototype of a perovskite/CIGS tandem thin-film solar module, exceeding the efficiency of individual perovskite and CIGS solar modules for the very first time.

To create the new solar module, the researchers used a stack module. By merging both perovskite and CIGS into one module, the new structure could benefit from the advantages of both technologies. The upper semitransparent layer of the model is made of perovskite, which absorbs high solar energy. Meanwhile, the lower CIGS layer is responsible for infrared conversion. Having an area of 3.67 square meters, the stacked perovskite/CIGS model is also designed to meet industrial needs. It features a monolithic interconnection scheme using 4 and 7 module cell stripes. Unlike other small-scale solar cells, the new stacked solar module can be interconnected for several square meters through laser processing.

Solar-Tectic, a thin-film specialist with patented technology primary focused on developing highly textured, single crystal semiconductor films on glass or other inexpensive substrates, presented a paper at the "Fifth International Symposium on Energy Challenges and Mechanics (ECM5) - working on small scales" in Inverness, Scotland, making public for the first time details of its perovskite/crystalline silicon thin-film tandem solar cell technology for highly efficient and inexpensive solar cells.

While reports of perovskite/silicon tandem solar cells are common, it would seem that there have been much less mentions of perovskite/thin-film silicon. Crystalline thin-film silicon promises to be less expensive than silicon wafer technology due to low temperature processing and less material use. Also, the entire process is non-toxic since tin (Sn) is used in the perovskite material, rather than lead (Pb).

Researchers at the Hong Kong Polytechnic University (PolyU) have reported reaching 25.5% efficiency with a perovskite-silicon tandem solar cell. In the tandem cell, a perovskite solar cell is placed on top so that it can harvest the short wavelength photons, while the bottom layer coated with silicon absorbs the long wavelength photons. To further increase the conversion efficiency, the research team has applied three innovative approaches, involving the use of low-temperature annealing, a tri-layer of molybdenum trioxide/gold/molybdenum trioxide, and a haze film.

The PolyU team believes that the cost of solar energy can drop significantly thanks to that concept, as compared to silicon cells available in the market. The PolyU research team will continue to work on further increasing the efficiency as well as the performance of large-scale fabrication of perovskite-silicon solar cells.

Researchers at the University of Toronto in Canada and ShangaiTech University in China have succeeded in using colloidal quantum dots in a high-mobility perovskite matrix to make a near-infrared (NIR) light-emitting diode (LED) with a record electroluminescence power conversion efficiency of nearly 5% for this type of device. The NIR LED could find use in applications such as night vision devices, biomedical imaging, optical communications and computing.

The researchers say that they may have found a way to overcome the known problem of low power conversion efficiencies (PCEs) of CQD-based LEDs, by embedding CQDs in a high-mobility mixed-halide perovskite matrix. The new composite allows for radiative recombination in the quantum dots by preventing charge carriers from becoming trapped in defects as they travel through the material, and this without increasing the turn-on voltage in a device. By carefully engineering the composition of the mixed halide matrix, the researchers made bright NIR CQD LEDs with electroluminescence PCEs of 4.9%. This value is said to be more than twice that of previously reported values for devices made from these materials, which means that with same amount of electricity it is possible to get twice as much NIR light power out.

A team coordinated by the Centre Suisse d'Electronique et de Microtechnique (CSEM) will work on a €5 million, three-year project to produce solar cells based on perovskite at a size of at least 15x15 cm, while maintaining a conversion efficiency of at least 14%.

In addition to this up-scaling, the research team will develop high-performance cells. Such tandem cells can harvest a broader spectrum of light than a single cell, which should lead to an increase in their efficiency further, approaching the 30% range. The team states that, in the longer term, existing manufacturing methods used to make silicon cells may require only minor modification before being used to produce tandem cells, as the perovskite layer would simply be added on top of the conventional cell to act as an 'efficiency booster'.

Researchers from the Universitat Jaume I and the Universitat de València have studied the interaction of two materials, halide perovskite and quantum dots, revealing significant potential for the development of advanced LEDs and more efficient solar cells.

The researchers quantified the "exciplex state" resulting from the coupling of halide perovskites and colloidal quantum dots. Both known separately for their optoelectronic properties, but when combined, these materials yield longer wavelengths than can be achieved by either material alone, plus easy tuning properties that together have the potential to introduce important changes in LED and solar technologies.

Researchers at EPFL have designed an ultra-sensitive carbon nanotube-based photodetector, sensitized with perovskite nanowires which make it highly responsive.

While carbon nanotubes are often used in photovoltaic and optoelectronic devices, light detection with pristine carbon-nanotube field-effect phototransistors is currently limited to the range of 10% quantum efficiency (the responsivity of the best carbon nanotube devices is around 0.1 A/W). Using perovskites, EPFL scientists have now fabricated a carbon-nanotube photodetector with responsivity as high as 7.7×105 A/W.

Researchers from an Oxford-Berlin (Helmholtz-Zentrum) collaboration reported that an ultimate efficiency of 30% should be attainable with perovskite-silicon tandem solar cells. They discovered a structurally stable perovskite composition with its band gap tuned to an optimum value of 1.75 eV.

Tandem solar cells work by absorbing the high energy photons (visible light) in a top cell which generates a high voltage, and the lower energy photons (Infra red) in a rear cell, which generates a lower voltage. This increases the theoretical maximum efficiency by about 50% in comparison to a standalone silicon cell. To maximize efficiency, the amount of light absorbed in the top cell has to precisely match the light absorbed in the rear cell. However, the band gap of ~1.6eV of the standard perovskite material is too small to fully exploit the efficiency potential of this technology.

Researchers at the Swiss materials science and technology research institute, Empa, have discovered a new way to produce thin film tandem solar cells using perovskite crystals. This discovery is a major milestone on the path to produce high-efficiency solar cells with low cost procedures.

In tandem solar cells, energy is harvested in two stages, which results in the conversion of sunlight into electricity becoming much more efficient. The top cell is semi-transparent and allows efficient conversion of large energy photons into electricity and the bottom cell converts the remaining transmitted low energy photons in an optimum manner. The tandem solar cells provide 20.5% efficiency when converting light to electricity and the researchers said that this can be increased to 30%. Empa researchers have further emphasized that it has a lot of potential to provide better conversion of solar spectrum into electricity.