Perovskites

 

There is a new buzzword in the photovoltaic market – Perovskite. It may be the holy grail that the solar power industry has been seeking. 90% of the photovoltaic cells today are Silicon based and they have already reached the theoretical maximum efficiency postulated by the Shockley – Quiesser limit.

Recently, Oxford PV, a start-up spawned by Oxford University, announced a record efficiency of 29.5% for a solar cell, compared to 15-25% for today’s commercial solar cells. The researchers achieved this incredible success by coating Silicon cells with a thin film of Perovskite.

Perovskite was originally a mineral discovered in the Ural Mountains of Russia in 1839 and named after the Russian mineralogist, Lev Perovski. Today it is synthesised in the laboratories and refers to a class of materials that have the same crystal structure as Calcium Titanate, the original mineral. A typical Perovskite structure is ABX₃, where A is an organic cation, B is a metal (usually lead) and X is a halide anion.

Oxford PV is boosting the cell efficiency by capturing more of the energy available in solar radiation. The thin Perovskite layer absorbs shorter wavelengths and Silicon absorbs the longer ones.

Perovskite has many other advantages. It is more tolerant of defects unlike silicon which is required in very high purity. Also it is needed in much smaller quantities. The Perovskite solar cell is thus likely to be much cheaper.

There are question marks on the stability of Perovskites in hot and saline environments and also their environmental compatibility. Besides Oxford PV, at least a dozen other start-ups are working on the Perovskite technology. Commercial rollout is likely in 2022.