Perovskite and organic photovoltaics

Tin oxide (SnOx) electron-extraction layers are fabricated via a reactive electron-beam evaporation process from a metal source under a partial pressure of oxygen. These are then used in standard (n-i-p) architecture perovskite solar cells and achieve power conversion efficiencies up to 19.3%.

The SnOx deposition process is performed onto substrates maintained at low temperature compared to similar techniques, with films not requiring any subsequent high-temperature post-deposition annealing. This demonstrates the potential compatibility of reactive electron-beam evaporation with roll-to-roll processing onto flexible polymeric substrates.

Ultrasonic spray coating is used to fabricate OSC devices based on a blend of the polymer PM6 with the Y-series acceptor DTY6. Using the non-halogenated solvent o-xylene, devices with PCEs of up to 14.1% are obtained. Wet film drying dynamics are controlled using an air-knife; a technique that has been demonstrated to be industrially scalable and has been used to “gas-quench” hybrid lead halide perovskite films in spray-coated cells and to assist drying in blade-coated OSCs.

Ultrasonic spray coating is used to fabricate perovskite solar cells (PSCs) over rigid, nonplanar surfaces without problems caused by solution dewetting and subsequent “run-off”. We fabricate devices over a convex glass substrate, with devices having a maximum power conversion efficiency of 12.5%. To our best knowledge, this study represents the first demonstration of a rigid, curved perovskite solar cell. 

Carbazole-based self-assembled monolayers are becoming a dominant hole-transporting layer in p-i-n perovskite solar cells, combining stability, efficiency, and low-cost. In article number 2104848 by David G. Lidzey and co-workers, spray coating and airbrush pen coating of MeO-2PACz is used to fabricate high-quality transport layers. This is combined with gas-quenched spray-coated perovskite layers, to realise solar cells with power conversion efficiencies in excess of 20%.

Work described in this paper demonstrates that the shelf-life of high-performing perovskite precursors can be greatly improved by storing solutions at low-temperature without the need to alter chemical composition. The front cover of ChemSusChem (shown above) shows a futuristic view of large-scale perovskite solar cell (PSC) manufacture. This includes a high-volume roll-to-roll printing facility and cold-storage of PSC precursor solutions in large industrial fridges.

A look toward the future of spray-coating perovskite photovoltaics. Our spotlight on applications discusses developments made over the last six years that have enabled the fabrication of increasingly high-performance spray-coated perovskite solar cells.

In particular, the various approaches adopted to spray-cast perovskite films (one-step vs. two-step processes) ware charted and the development of sophisticated techniques used to control thin-film crystallinity is described. Finally, remaining research challenges are discussed that - once solved -may allow the mass deployment of low-cost solar energy.

In conjunction with Power Roll Ltd, EPMM have developed flexible, back-contact perovskite-based photovoltaic devices utilising a new, patented V-groove architecture. These devices are in principle easy to manufacture and do not include any rare-earth metals.

This perspective summarises the developments in spray-cast perovskite solar cells made over the past few years, with particular attention paid to strategies employed to control the crystallisation of the perovskite. Steady progress has now been made with spray-cast perovskite PV devices recently demonstrated having a power conversion efficiency of 18.3%. We highlight trends within the research field and discuss challenges that will be necessary to drive such techniques toward practical application.