Researchers from the Los Alamos National Laboratory have found a way to produce perovskite thin films, using a low-cost, scalable technique
Perovskites are the latest buzzword in solar power. Named after a Russian mineralogist called Lev Perovski, their crystal structure – similar to that of CaTiO3 – along with their optical and electrical properties, have seen them touted for use in a number of optoelectronic applications. Originally suggested for use in printed, thin-film solar cells in 2009, their power conversion efficiency has increased from below 5% to over 20%, and progress shows no sign of slowing.
With techniques such as spin-coating being used to produce these crystalline films, they’ve so far been limited to small-area proof of principle devices. But a paper published in a recent issue of Applied Materials Today [DOI: 10.1016/j.apmt.2016.03.0021], showed that doctor blading (also known as knife coating) could be used to reliably grow large-area perovskite films.
Doctor blading is a process whereby a coating is applied using a moving blade set at a fixed height from a surface. Already widely used in roll-to-roll processing, it is a straightforward way to control the thickness of a film. To investigate the effect of the process on perovskite crystal growth, the Los Alamos team varied substrate temperature, solution volume and blade speed. They found that the size of the perovskite ‘islands’ that formed in the film was strongly correlated to the temperature of the substrate, with the largest grown at 165°C. A high blade speed (up to 60mm/s) was found to increase both the thickness and the roughness of the final film, and the larger the volume of solution used, the larger the eventual islands were.
A film that optimised these characteristics was then used to produce perovskite solar cells, and their performance was analysed. At 7.23%, the maximum power conversion efficiency is lower than others in the literature, but these cells show none of the current-voltage hysteresis that other perovskite cells suffer from. This makes them considerably more reliable over the long term. In addition, across batches of these cells, the performance was consistent (the standard deviation of the efficiencies was just 0.42%), suggesting that their approach to producing large-island thin films is highly reproducible. Work is ongoing, but the team are confident – they believe that these results could “pave the way to achieve large-scale production of highly efficient perovskite solar modules.”
— This article first appeared on the Materials Today site on 20th April 2016. You can read it there by following this link: http://www.materialstoday.com/energy/news/printable-perovskite-solar-cells/
— Original research paper: A.T. Mallajosyula, K. Fernando, S. Bhatt, A. Singh, B.W. Alphenaar, J-C. Blancon, W. Nie, G. Gupta, A.D. Mohite, “Large-area hysteresis-free perovskite solar cells via temperature controlled doctor blading under ambient environment”, Applied Materials Today 3 (2016) 96–102. DOI: 10.1016/j.apmt.2016.03.002