Prof Henry Snaith FRS

Abstract:

Nanomaterials with different morphologies were placed in discrete layers through the thickness of a negative electrode for a Li ion battery to exploit effectively the intrinsic energy storage capabilities of each nanomaterial morphology and to improve the overall dynamics of Li ion diffusion. The two layer electrode showed a combination of high volumetric capacity and rate capability that surpassed the performance of conventional randomly blended electrodes comprising the same nanomaterials. Local Li ion concentrations were measured through the electrode thickness and clearly showed the benefits of the layered structure over the alternatives. The two layer electrode was fabricated by a flexible and scalable suspension atomization and spray deposition technique with generic potential for improved layered electrodes in a wide range of applications.

Abstract:

Since the first reports of solar cells with power conversion efficiencies around 10% in 2012, the science and technology of perovskite photovoltaics has been progressing at an unprecedented rate. The current certified record efficiency of 22.1% makes perovskites the first solutionprocessable technology to outperform multicrystalline and thin-film silicon. For this technology to be deployed on a large scale, the two main challenges that need to be addressed are the material stability and the toxicity of lead. In particular, while lead is allowed in photovoltaic modules, it would be desirable to find alternatives which retained the unique optoelectronic properties of lead halide perovskites. Here we offer our perspective on the most exciting developments in the materials science of new halide perovskites, with an emphasis on alternatives to lead. After surveying recent developments of new perovskites and perovskite-related materials, we highlight the potential of halide double perovskites. This new family of compounds constitutes uncharted territory, and may offer a broad materials library for solar energy applications.

Abstract:

Optoelectronic devices based on hybrid halide perovskites have shown remarkable progress to high performance. However, despite their apparent success, there remain many open questions about their intrinsic properties. Single crystals are often seen as the ideal platform for understanding the limits of crystalline materials, and recent reports of rapid, high-temperature crystallization of single crystals should enable a variety of studies. Here we explore the mechanism of this crystallization and find that it is due to reversible changes in the solution where breaking up of colloids, and a change in the solvent strength, leads to supersaturation and subsequent crystallization. We use this knowledge to demonstrate a broader range of processing parameters and show that these can lead to improved crystal quality. Our findings are therefore of central importance to enable the continued advancement of perovskite optoelectronics and to the improved reproducibility through a better understanding of factors influencing and controlling crystallization.

Abstract:

Multi-junction solar photovoltaics are proven to deliver the highest performance of any solar cell architecture, making them ideally suited for deployment in an increasingly efficiency driven solar industry. Conventional multi-junction cells reach up to 45% efficiency, but are so costly to manufacture that they are only currently useful for space and solar concentrator photovoltaics. Here, we demonstrate the first four and two-terminal perovskite-perovskite tandem solar cells with ideally matched bandgaps. We develop an infrared absorbing 1.2eV bandgap perovskite, FA0.75Cs0.25Sn0.5Pb0.5I3, which is capable of delivering 13.6% efficiency. By combining this material with a wider bandgap FA0.83Cs0.17Pb(I0.5Br0.5)3 material, we reach initial monolithic two terminal tandem efficiencies of 14.0 % with over 1.75 V open circuitvoltage. We also make mechanically stacked four terminal tandem cells and obtain 18.1 % efficiency for small cells, and 16.0 % efficiency for 1cm^2 cells. Crucially, we find that our infrared absorbing perovskite cells exhibit excellent thermal and atmospheric stability, unprecedented for Sn based perovskites. This device architecture and materials set will enable “all perovskite” thin film solar cells to reach the highest efficiencies in the long term at the lowest costs, delivering a viable photovoltaic technology to supplant fossil fuels.