Tagged: Kesterite

Beginner’s guide to kesterite (CZTS) solar cells

Life was comfortable back in 2007. While starting to work on quaternary semiconductors for thin-film solar cells, there was very little literature. It was possible to read all of the papers in the field. Since the report of a 10% efficient solar cell made from Cu2ZnSn(S,Se)4 in 2010, interest in the field exploded and there now stands over 1000 publications. I feel sorry for any new graduate student beginning a project…

CZTSFrom a Web of Science search for “Kesterite OR CZTS solar cell” with 1155 results – 28th May 2015

From reading quite a few of these papers and attending conferences and workshops over the years, here is a decent reading list to get started:

1. Development of CZTS-based thin film solar cells (Thin Solid Films, 2009) – An important historical overview of the development of the field. Like many technologies, it all started in Japan.

2. New routes to sustainable photovoltaics: evaluation of Cu2ZnSnS4 as an alternative absorber material (Physica Status Solidi B, 2008) – An important paper from Jonathan Scragg (whose PhD thesis turned into the first book on kesterite solar cells) with layers made by electrodeposition.

3. The crystal structure of kesterite type compounds: A neutron and X-ray diffraction study (Solar Energy Materials and Solar Cells, 2011) – X-ray diffraction has trouble distinguishing between Cu and Zn. Neutron diffraction confirms the ground-state crystal structure (not stannite) and the tendency for cation disorder.

4. Kesterite Thin-Film Solar Cells: Advances in Materials Modelling of Cu2ZnSnS4 (Advanced Energy Materials, 2012) – The complexity of these materials has provided a fertile ground for theory and simulation, with early efforts reviewed here on structure, defects and band energies.

5. 8.6% Efficient CZTSSe Solar Cells Sprayed from Water–Ethanol CZTS Colloidal Solutions (Journal of Physical Chemistry Letters, 2014) – simple, clean and easy to scale up, with more recent reports of reproducible 10% efficiency from this approach.

6. Device Characteristics of CZTSSe Thin-Film Solar Cells with 12.6% Efficiency (Advanced Energy Materials, 2014) – The current record device with 12.6% efficiency. The one to beat!

7. Influence of compositionally induced defects on the vibrational properties of device grade CuZnSnSe absorbers for kesterite based solar cells (Applied Physics Letters, 2015) – Precision Raman spectroscopy is becoming increasingly useful for identifying secondary phases and quantifying structural disorder in kesterites. The team at IREC are leading the way.

8. Suns-VOC characteristics of high performance kesterite solar cells (Journal of Applied Physics, 2014) – What is limiting performance to less than 20%? This is one of several important detailed charactertisation papers that point to issues with the back contact.

2012 (Part Three)

Spring is the time for the best research ideas; summer is the time for writing up the work; autumn is the time for peer-review and winter is time to reap the rewards. The bounty of the last few months:

The first publication written by my first PhD student (an iconic moment). Lee has spent a year making sense of both experiment and theory of tin sulfides towards applications in solar cells. One of his early findings was that the recently reported zinc-blende phase cannot exist (based on thermodynamic, crystallographic, computational and chemical grounds).

Attending the recent European Kesterite Workshop was inspiring: many groups across the continent working towards the common goal of low cost and sustainable solar energy.  The defect chemistry of the quaternary semiconductor Cu2ZnSnS4 (CZTS) is epic; in the latest chapter we have identified a number of defect complexes that are likely to impact the performance in CZTS solar cells.

When my long-time collaborator Russ Egdell visited Bath for a seminar last summer, we sat down to discuss our on-going projects. One issue he had was understanding why the material CuCrO2 adopted a peculiar orientation (015) when grown on Al2O3 substrates. With the aid of  crystal structure visualisation and a few back-of-the-envelope calculations we were able to explain it in a few hours. This nice paper is the result!

The first publication written by my second PhD student (another iconic moment). A first step towards systematically tuning the electronic properties of metal organic frameworks. From screening 24 compounds, five potential hybrid semiconductors were identified.