November 2015

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.

Dyesol, the Australia-based Perovskite Solar Cell (PSC) technology developer, aims to raise up to AUD 10 million (USD 7.25 million/EUR 6.8 million) by selling shares to shareholders and investors.

A share purchase plan (SPP) opened on November 19, allowing existing shareholders from Australia or New Zealand to subscribe to new shares priced at AUD 0.26 a piece. The SPP targets AUD 6 million in proceeds, to support Dyesol's Technology Development and Business Activity plans and working capital. The SPP is expected to close on December 4.

Florida State researchers have developed a cheaper, more efficient LED, or light-emitting diode, using perovskites.

The researchers spent months using synthetic chemistry to fine-tune the materials in the lab, creating a perovskite material capable of emitting a staggering 10,000 candelas per square meter when powered by 12 volts. The scientists say that such exceptional brightness owes, to a large extent, to the inherent high luminescent efficiency of this surface-treated, highly crystalline nanomaterial.

Researchers from Helmholtz-Zentrum Berlin (HZB) and the university École polytechnique fédérale de Lausanne(EPFL) in Switzerland have combined a silicon heterojunction solar cell with a perovskite solar cell monolithically into a tandem device and reached a record efficiency of 18%, stating it has the potential to reach 30% after additional modifications.

Designing such silicon-perovskite tandem cells can be challenging, as perovskite cells tend to require coating onto titanium dioxide layers, which must first be sintered at around 500 °C. The amorphous silicon layers that cover the crystalline silicon wafer in silicon heterojunction degrade at this temperature. Now the team from EPFL and HZB has managed to overcome hurdles and manufacture this kind of monolithic tandem cell, by depositing a layer of tin dioxide at low temperatures instead of using titanium dioxide. A thin layer of perovskite could then be spin-coated onto this intermediate layer and covered with hole-conductor material. The team also used a transparent protective layer to avoid the metal oxides sputtering and consequently destroying the perovskite layer and hole-conductor material.

A research team from Japan's National Institute for Materials Science (NIMS) has developed a new method of fabricating high-quality perovskite materials, capable of utilizing longer-wavelength sunlight of 800 nm or longer. The method may mark a new approach to enhance the efficiency of perovskite solar cells.

Perovskite solar cells currently possess optical absorption spectra that lean toward shorter wavelengths. To improve the energy conversion efficiency of these cells, it is crucial to develop perovskite materials with optical absorption spectra expanded to include longer wavelengths. This is why several research institutes are developing perovskite materials that include two types of cations, MA and FA, capable of absorbing light in the longer wavelength region. However, these cations are not without issues - mainly that their mixing ratio and crystallization temperature are difficult to control. Moreover, due to their tendency to form a mixed crystal phase, there had been no effective method established to fabricate high-purity, single-crystalline perovskite materials.

Researchers at the Swiss EPFL are working on developing a perovskite-based material that can convert light and X-rays into electricity and holds great potential for use in photovoltaics as well as space exploration.

The scientists have chosen to use methylammonium lead iodide (CH3NH3PbI3), a material already used in conventional perovskite solar cells, where it harvests visible-light photons that are then converted into electricity. They fabricated single crystals of methylammonium lead iodide and tested them on photocurrent generation while irradiating them with X-rays, where they found 75% charge-collection efficiency in millimeter-sized crystals. This high-efficiency current conversion for X-ray radiation also matched the material's high X-ray absorption coefficient.

Scientists at the National Institute for Materials Science (NIMS) announced the improvement of power conversion efficiency (PCE) of perovskite solar cells to over 16% while employing cells that were greater than 1 cm2. The high efficiency cells also passed the durability test (exposure to AM 1.5G 100 mW/cm2 sunlight for 1,000 hours), which is considered to be a basic criterion for practical use. These achievements were made by replacing the conventional organic materials with inorganic materials as the electron and hole extraction layers of the solar cells.

The researchers replaced the conventional organic materials with robust inorganic materials for use in electron and hole extraction layers. Since these layers have high electrical resistance, it was necessary to reduce the thickness of the layers to several nanometers. However, as the area of these thin layers increases, the occurrence of defects called pinholes also increases, leading to decreased PCEs. To deal with this problem, the researchers increased the electrical conductivity of these layers by more than 10 times through heavily doping both electron and hole extraction layers. In this way, they fabricated layers that have fewer pinholes over wide areas and are applicable at thicknesses of up to 10 to 20 nm. Using these layers, a PCE of 16% was repeatedly attained while employing cells that were greater than 1 cm2. The use of inorganic materials also contributed to PCE reduction within 10% even after undergoing 1,000 hours of continuous exposure to sunlight at an intensity of 1 sun, demonstrating outstanding reliability.

A team of Swiss, Chinese and Japanese researchers has found a way to scale up perovskite solar cells without a loss of stability. Instead of changing the perovskite, the researchers added a new element to the device, a thin film light collector that is placed over the cells.

The film was constructed in two layers, one a positively charged cubic rocksalt semiconductor, the other a sheet of negatively charged titanium oxide. Arriving light causes the perovskite layer to be excited, which results in freed electrons moving through the titanium oxide layer on one side of the film while holes are transported through the other. The result is a protective film covering that actually increases conductivity of the device.

Researchers at the National Renewable Energy Laboratory (NREL) announced that they have figured out a pathway for dealing with the heat loss problem by deploying hot-carrier technology in perovskite solar cells. Hot carrier solar cells offer simplicity of design, low cost, and high efficiency, but are a long way from being commercialized, as one big challenge is revving up the kinetic energy transfer in order to prevent energy loss.

This recent study provides a pathway for pushing perovskite levels upwards, possibly as high as 66%. It determines that charge carriers created by absorbing sunlight by the perovskite cells encounter a bottleneck where phonons (heat carrying particles) that are emitted while the charge carriers cool cannot decay quickly enough. Instead, the phonons re-heat the charge carriers, thereby drastically slowing the cooling process and allowing the carriers to retain much more of their initial energy for much longer periods of time. This potentially allows this extra energy to be tapped off in a hot-carrier solar cell.