19 05 2014

Another question – ‘I was wondering if you could possibly do an example of an example of calculating Pmax for a solar cell please‘.

This one needs a bit more explanation than a one liner – so here goes.  Starting with the circuit schematic for the solar cell with a load resistor, which can be found in figure 11.3



Hence, the current through the load resistor is the photo-current (IL) and a reverse direction p-n junction, which is described by Shockleys equation (see the second year notes!).  This gives equation 11.1.


From this, it is possible to calculate the short circuit current, by setting the voltage term in Shockley’s equation to zero, giving equation 11.3 – but realise that a lot of the terms at the front of the equation are in fact Is – the saturation current!


You can also balance the two currents (IL and the p-n junction) to get Voc (i.e. the voltage when no current flows) and so this gives equation 11.2


Having got all this, the last step is to look at the maximum power.  Because you get zero power at Isc (because V=0) and at Voc (because I=0) there is a voltage and current at which the maximum occurs and this is given by Voc x Isc x FF.  Here the fill factor (FF) is an experimentally extracted value (quoted to you if required)


SiC Movie Stars!

30 01 2013

Tomorrow sees the official launch of the UK’s first silicon carbide foundry. Raytheon Uk have been busy updating their facilities to offer a complete foundry service for 4″ SiC wafers. This is running alongside their development of SiC CMOS, a project leading the realisation of 400C CMOS strcutures, from amplifiers to digital circuits.
As part of this big launch, two of our colleagues from Raytheon have found themselves on YouTube explaining the benefits from the use of SiC in high temperature electronics. The video of Robin and Ewan can be found here.

First MoS2 results

28 01 2013

This is the first of the spectra from our MoS2 experiment last week. Having peeled our layer until it was only just visible, we transferred it over on to a SiO2 covered wafer and after a quick look under the microscope we went to our Raman system. The microscope image is the inset to the image, showing the flakes we examined with Raman. The spectra shown in for the large flake in the upper centre of the image

Raman MoS2 spectra

Raman Spectra of a MoS2 flake

The peak shape is interesting, unlike previously published results, we see a higher intensity for the A1g peak in comparison to the E1g peak. As an example, the left hand hand inset is from S. Najmaei et al, (Applied Physics Letters, 100, 013106). Their work details the expected separation between the two Raman peaks and enables the determination of the number of layers. Our separation of 25.6cm-1 indicates that we have bulk material, so it would appear that in addition to enhancing the lateral dimensions of the flakes, we need to continue peeling for longer!

Annual Research Conference – The Highlights

28 01 2013

Last weeks internal research conference was a great success. Not only was it the first time that I haven’t been dragged into the organisation, but we made a good job of winning the prizes …

Sandip narrowly beat Neal to the poster prize with his work on the development of gas sensor arrays, following on from Ben Furnival.

SiC gas array high temperature

The winning poster

Neal took second with his work on amplifier structures for hostile environments, an area which will support a lot of our other work in sensor development.

SiC amplifier hostile environment

SiC Amplifier structures

On top of this, Lucy won the best presentation award, beating Karthik into second place. Her presentation used Prezi, which was something new to me and judging by the comments in the audience was new to most of us. She then went on to win the second best paper prize, making it a good day out for us all.

Research Conference

24 01 2013

Today saw the start of the internal research conference and I’ve been persuaded to give a talk tomorrow. The topic of which is our recent interest, Molybdenum Disulphide. Having spent the afternoon in the cleanroom playing with Scotch tape and trying to make an atomic layer, this is something for the future ?ARC Talk


22 01 2013

As promised, here is the update for the exciting news in 2013.

At the end of 2012, we joined the space exploration project being run by JP Aerospace in California and launched some pongsats with our local scouts. We flew all kinds of stuff, from bouncy balls to a troll (don’t ask) in our balls, but perhaps the most interesting was the six axis solar intensity monitor. This was built by a work experience student, who managed to make it onto the BBC local news back in October. This was so successful, we got the bug and when we saw the ‘Ideas Take Flight‘ strapline for the upcoming British Science Festival, the thought was ‘how high?’

This has resulted in a big project, with some twenty teams developing cubesats to launch up to around 100,000 feet sometime in June

British Science Festival space cubesat ideas

Ideas Take Flight … to the Edge of Space

So far, we have held a big kick off event in the Discovery Museum and followed this up with visits to schools and this last week, schools visiting us. Next step, is that we need to think carefully about the circuitry before we all meet up again to squeeze it all in to a 2″ cube.

The last update for today, is that I received my new toy in the post yesterday. Molybdenum Disulphide, potentially the next graphene, is being touted as the next wonder material. A trip to the clean room tomorrow and hopefully we should be up and running in this exciting field by this time next week.

MoS2 Molybdenum Disulphide crystal 2D electronics

Natural Molybdenum Disulphide Crystals

An experiment …

2 01 2013

More of a social experiment than the usual sparks and destruction fest which can be found in the lab. I’ve been having a bit of a play with the Mendeley desktop over Christmas. I’ve been really impressed with the flexibility of how you can grab and drop pdf files of journal articles (and anything else) and the sync feature means I have my reading list on both computers and iPad. At last, something worthwhile to read in meetings (although – I have been playing with the NASA app and the the NASA visual app in meetings for a while now)
As part of my playing with Mendeley, I have decided to try creating a group with a view to gauging the level of interest for research into Molybdenum Disulphide. This miracle material offers some significant advantages over graphene (a bandgap for example) and recent results from EPFL have demonstrated some pretty decent transistor characteristics. Hopefully, this new group (called Molybdenum Disulphide – original I know) will attract enough interested parties and then we can take it from there and branch out into other areas of our research.