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 are currently recruiting for a new post doc in the field of micro-solar cells. The position is for two years with an extendable contract. The post doc will also have the opportunity to help co-ordinate the research of a doctoral training unit in advanced photovoltaic concepts also involving tandem solar cells. For more details please contact Phillip Dale.

 

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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