Henry Snaith comments of the status of perovskite pv in Nature Materials

The comment article by Henry Snaith provides an overview of the rapid development of Perovskite Photovoltaics that has taken place. Since 2012 when metal halide perovskite were first used their power conversion efficiency is already approaching 23% for a single junction cells.

Improving long-term stability - about 25 years - requires further understanding of the optoelectronic properties of metal halide perovskite devices and how they can be controlled with further chemistry and device architecture optimisation.

Moving beyond single-junction solar cells will a be achieved adopting advanced concepts. These include multi-exciton generation, single fission, hot-carrier collection and even intermediate band-gap cells

A near-term option to improve efficiencies is to use multi-junction concepts, in which perovskite films are combined with silicon or other materials to expand the absorption spectral range.

Perovskite compounds are largely held together through ionic bonding, a likely factor for the high tolerance to crystalline defects and the ease at which highly crystalline films can be formed at low temperature. However, this also results in lower decomposition temperatures making the materials intrinsically less thermally stable than silicon. A few potential routes have emerged to stabilise these frameworks with inorganic ions. More work is required to confirm if these or other approaches can lead to long term stable inorganic perovskites.

The rise of efficient metal halide PV cells has seen creased interest in discovering new materials. Driven by the desire to replace lead. At present the partial replacement of lead with tin is the only route to reduce the band-gap to below 1.5eV - essential for multi-junction cells.

As perovskite research advances there has been an increase in patenting activities as companies and research institutions seek to protect their innovations. The top ten assignees show the truly global nature of research and development on Perovskite photovotlaic technologies with patents are being filed by commercial organisations and academic institutions in Europe, Japan, Korea, China, USA and Australia.

Current initiatives to support perovskite development lack ambition and scale. This may be due to perovksite pv technologies being a relatively young technology and due to the inherent inertia and time lag in strategic investments decisions. Although there has been 3,000 academic papers published on perovskite PV these have mainly been funded from small grants rather than large ambitious multilateral projects.

Barriers to commercialisation do exist. The most significant ones are probably not technical, but commercial - specifically raising finance. The amount of investment required to move from promising research results to manufacturing ready technology requires an order of magnitude in investments. The failure of past PV technology investments made during the early 2000s has made current investors cautious in making a commitment to perovskite pv. Perovskite PV holds great promise as a source of energy generation and is unlikely to replaced any time soon.

Investors should recalibrate their perspective on PV in light of the overall progress being made and the long-term potential that perovskite PV technologies offers.

In conclusion, Henry Snaith said that there has been tremendous research activity in metal halide perovskites for PV applications over the past six years, which has resulted in many discoveries and advances. Although expanding upon the lead halide material set has proven challenging, improving the quality and stability of the lead halide perovskites and devices has brought the technology tangibly close to commercial readiness.

There is now growing industrial momentum and it is likely that real PV applications employing metal halide perovskites will be demonstrated over the next few years, which will represent a second phase, or era, for this research community.