Perovskite - the new photovoltaic on the block

Move over graphene – there’s a new kid on the photovoltaics block – and it can be spray-painted. Spray-painting has been used to produce solar cells using organic semiconductors, but this is the first time perovskite has been used – with promising results. “There is a lot of excitement around perovskite based photovoltaics,” said lead researcher Professor David Lidzey from the University of Sheffield. “Remarkably, this class of material offers the potential to combine the high performance of mature solar cell technologies with the low embedded energy costs of production of organic photovoltaics.” “The perovskite devices we have created still use similar structures to organic cells,” Lidzey added. “What we have done is replace key light absorbing layer – the organic layer – with spray painted perovskite. Using a perovskite absorber instead of an organic absorber gives a significant boost in terms of efficiency.” [caption id="attachment_39366" align="alignright" width="200"] The two spray heads, plus the gantry it moves on at the top (it can move in both x and y directions whilst spraying so can do any pattern you want). The substrates are placed on a hot plate (just visible in the bottom of the photo) and the head scans across them whilst spraying. We can program the head to spray just once, or to do multiple passes at different speeds, heights etc. Copyright: Alex Barrows.[/caption] Spray painting wastes very little of the perovskite and the technique can be scaled up to high volume manufacturing using similar methods to those employed in spraying cars. But implementing the technique wasn’t easy. “We had to do quite a lot of optimisation of the process in order to get the perovskite material to form a reasonably uniform, smooth layer without many gaps in it. This is essential for getting the best efficiencies from a solar cell,” PhD student Alex Burrows told Laboratory News. “By controlling the temperature of the glass that we were spraying onto, the speed of the spray-head and the solvents we were spraying the materials from we've managed to find a method whereby this can be achieved.” The technique allowed researchers to make prototype solar cells with an efficiency of up to 11%. “There are still significant improvements to be made – at the moment the layers we're spraying cover about 85% of the surface beneath them, leaving a number of small gaps or pinholes in the layer,” added Burrows. “We're currently experimenting with a number of new methods in order to try to improve that, which would give us greater light absorption and reduce other losses of potentially useful energy in the device.” [caption id="attachment_39367" align="alignleft" width="200"] Diagram illustrating how the spraying works. Copyright: Jon Griffin.[/caption] “There are still significant improvements to be made – at the moment the layers we're spraying cover about 85% of the surface beneath them, leaving a number of small gaps or pinholes in the layer,” added Burrows. “We're currently experimenting with a number of new methods in order to try to improve that, which would give us greater light absorption and reduce other losses of potentially useful energy in the device.” “I believe that new thin-film photovoltaic techniques are going to have an important role to play in driving the uptake of solar-energy, and that perovskite based cells are emerging as likely thin-film candidates,” added Lidzey.