The lab-scale highly efficient perovskite solar cells (PSC) are outperforming many conventional alternatives due to their outstanding optoelectronic properties; however, lab scale fabrication still suffers from high material wastage and scaling challenges [1]. Along with high efficiency perovskite photovoltaics are solution processable and therefore have the potential commercially relevant high-volume manufacture through printing processes.

Scaling up of PSC layers has been demonstrated in recent years through a variety of printing methods yet Roll-to-Roll coating with the slot die coating method shows the greatest promise. Slot-die coating is a cost-effective coating method that allows significant control in coating and can deposit layers with little material wastage, high control on film thickness, and flexibility to coat layers with 2-dimensional patterning. The transition of PSC from lab scale spin coating to industrial scale slot die coating is not trivial with consideration of solution compatibility, rheology and process modelling needed for individual layers [2]. Combining these methods roll to roll slot die coating of active layers including HTL, Perovskite and ETL in combination has resulted in device performances of 12.2% [3] at pilot scale under ambient atmosphere processing.

However, unlocking the potential of industrial scale, high volume, and continuous manufacture of perovskite solar cells requires all layers to be sequentially coated, including the back electrode instead of the high value evaporated metal contacts employed as a post process.

Recently, we demonstrated the Roll-to-Roll slot-die coating of a full n-i-p device stack completed with a sequentially slot die coated carbon electrode [4]. Two developments were critical in achieving this world’s first, formulation of carbon ink electrode and introduction of a low temperature stable interlayer. The formulation of the carbon ink was through two stages, the compatible, non-toxic, low boiling point solvent system was proved through stencil coating on spin coated samples. The carbon ink was then re-formulated for slot die coating before the full stack was sequentially coated. The low-temperature curing PEDOT interlayer between perovskite and carbon electrode analysed by EIS and PL measurements overcomes interlayer incompatibilities and recombination losses achieving 13-14% at small scale retaining over 80% efficiency over 1000hrs stability testing. XPS elemental lead mapping and EL emission photography of R2R coated SnO2/MAPI/PEDOT are also indicate that the coverage is effective and covers high points so as to prevent pinhole/shorting defects. Our work introduces the fabrication pathway, challenges, and achievements of the very first all-printed Roll-to-Roll perovskite device achieving over 10% efficiency, a game-changer in the commercialization of this generation of solar cells.

Keyword: Roll-to-Roll, carbon electrode, perovskite, PEDOT