Energy Materials

At the Laboratory for Energy Materials (LEM)  we are interested in making and testing complex materials necessary for energy conversion and storage using low cost and innovative methods.

Currently our research is focused on the preparation and characterization of p-type semiconductor absorber layers for use in thin film solar cells. Its main scientific goal is to understand how to convert a simple precursor layer into single phase high quality semiconductor material.

  • Precursor layers are synthesized with two techniques (I) electrodeposition and (II) spin coating nano particles.
  • High temperature electrodeposition allows the direct deposition of p-type semiconductors.
  • Precursor layers are converted into semiconductor thin films by the application of energy using either heat or light irradiation. The Laboratory for Energy Materials studies whether annealing is possible within 1 second.
  • A quality assessment of semiconductors using photo-electrochemistry allows the discriminiation of suitable layers for devices.
  • LEM researchers try to understand the growth processes in terms of structural, thermodynamic and kinetic parameters. 

The Laboratory for Energy Materials is headed by Prof Phillip Dale.

 

JOB ANNOUNCEMENT

 

We have funding for a new project in semi-transparent photovoltaics (STPV) for use in buildings. The use of glass in buildings is increasing and there is an opportunity to create devices which utilize some of the light for photovoltaic power generation, and some of it for illuminating the interior of the building. Contrary to other approaches, our STPV design should allow a continuous view, and a natural daylight spectrum, whilst still generating renewable energy. The project is in collaboration with the International Iberian Nanotechnology Laboratory  based in Portugal, with plenty of exchange visits expected. We are looking for one post doc.

The post doc will be responsible for mini module design, optical and electrical simulation, and fabrication. The ideal candidate would thus demonstrate their ability to simulate and fabricate semiconductor  devices. The candidate should have a Ph.D or previous post doctoral background in solid state device physics with some familiarity of materials characterization. The candidate should have an excellent publication track record. The candidate must have a strong command of English. The ideal candidate would have worked with photovoltaic devices previously. The candidate should be prepared to travel between Luxembourg and Portugal to carry out a strong collaboration. Please contact phillip.dale@uni.lu directly.

 

RECENT NEWS

  • April 2018 : Synthesis, theoretical and experimental characterisation of thin film Cu2 Sn1-x Gex S3 ternary alloys (x = 0 to 1): Homogeneous intermixing of Sn and Ge

If solar cells could be made from widely abundant materials then there would be no reason why they could not be installed on a massive scale. Dr Erika Robert has been researching a new semiconductor, Cu2 SnS3 , which can be used to absorb light inside of a solar cell to start the process of generating electricity. In her latest paper in the journal Acta Materialia, she describes the synthesis and characterisation of thin film Cu2 Sn1-x Gex S3 ternary alloys (x = 0 to 1). The alloying of the novel p-type semiconductor Cu2 SnS3 with germanium Ge appears to improve solar cell light to electrical power conversion efficiencies up to around 6%. However, despite first satisfactory devices, the basic properties of these alloys, such as their crystallographic structure and bandgap, were prior to this work scarcely studied. In order to assess the alloys properties over a wider range, a library of samples over the whole composition range were produced.

The synthesized thin film compounds appear to form a solid solution over the entire compositional range (x = 0 to 1). Le Bail analysis of the X-ray diffractograms confirmed the monoclinic crystal structure of all the alloys and enabled the extraction of all lattice parameters, which decreased linearly with increasing Ge content. Conversely photoluminescence measurements showed the band gap increasing linearly with increasing Ge. Raman modes for the alloys were also calculated and showed fair comparison to experimental spectra, with newly reported peaks between 50 and 250 cm-1 . The manuscript also presents electrical measurements, showing a constant and high doping density, which requires reduction for future device applications.

 Caption for the picture: Conventional monoclinic unit cells of Cu2 SnS3 (left) and Cu2 GeS3 (right), and evolution of lattice parameter, doping density and bandgap energy as function of x in Cu2Sn1-xGexS3.

 Link for journal article

  • February 2018 : Article published in Nature Communications

Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers

Photovoltaic solar panels convert sunlight into electricity. For this to happen, sunlight must be absorbed by an active component called the absorber. In absorber materials, the incident light is able to excite electrons. One type of absorbers is made of many small grains packed into a thin layer (typically one hundred times thinner than a hair). The grains contain several chemical elements (such as copper, indium gallium and selenium). In the type of absorber investigated here, the depth distribution of these elements is designed to direct the flow of electrons excited by the sunlight, so that the maximum electricity power can be generated.

In simple terms, this work shows that if the absorber is made of only one grain, adding a small amount of sodium helps to homogenize the distribution of the elements. This is very surprising, because more than 20 years of previous research have consistently shown the opposite effect on absorbers made of many grains. Thanks to these results, we can now conclude that sodium has a dual effect: it homogenizes the elements inside each grain but it slows down homogenization from grain to grain.

You can freely download the article here

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