Large-area transparent conductors – thin films of optically transparent and electrically conductive material – are important components in a number of applications including thin-film solar cells, traditional liquid-crystal displays and organic light-emitting diodes. With EU funding of the project OHMIO, researchers worked on a new sustainable flexible conducting polymeric material with high transparency that can be used to make cheaper and more efficient organic solar cells amongst others electronic devices. Work was undertaken by SME Intenanomat S.L. that was founded in 2010 from the Institute of Materials Sciences of the University of Valencia. The company’s new product, Ohmidot™, is a highly flexible, transparent polymeric material that efficiently conducts electricity and overcomes problems related to other materials existing in the market. The barrier to perovskite solar cell commercialisation Perovskite solar cells have significantly improved in power conversion efficiency since their advent. However, further improvement relies on optimising hole-transport materials – their incorporation in perovskite solar cells is crucial to improve device performance and operational stability. “Such materials play a key role because they selectively improve hole transport efficiency, block electron transfer to the anode, and avoid degradation at the metal-perovskite interface,” explains Pedro Rodríguez Cantó, responsible for research and development at Intenanomat. Typical hole-transport layers include a polymer mixture of two ionomers called PEDOT:PSS. Due to its unique combination of excellent conductivity, transparency, ductility, and ease of processing, it has become a benchmark material in thin-film photovoltaics. On the downside, commercial PEDOT:PSS formulations can be highly acidic, such that humidity can significantly increase the corrosion rate of adjacent layers in the device. This limits the shelf-life of the perovskite solar cell, making its trajectory to the commercial stage significantly more difficult. Skirting limitations Project researchers managed to get past these limitations. This should raise a cheer as the perovskite solar cell industry received the much needed boost. “OHMIO’s technology is a disruptive innovation with a strong impact on the manufacturing cost, lifetime and performance of the latest-generation flexible electronic devices,” notes Rodríguez Cantó. Ohmid™ is formulated in liquid with selective additives and eco-friendly solvents. The formula eliminates the use of water as this would degrade adjacent layers, reduce the useful life of the device, and cause poor film forming. This also allows manufacturers to coat and print transparent conductive polymers on different types of substrates more efficiently using common coating and printing technologies. In addition, the formula does not contain acids or other elements that cause corrosion problems. Application areas Ohmidot™ can be formulated to adapt to any perovskite solar cell architecture. Its ability to improve solar cell efficiency is related to its high transparency to the visible but especially the near-infrared which is 30 % higher compared to that of industry standard material PEDOT:PSS. Rodríguez Cantó further explains, “Ohmidot™ significantly reduces production costs of solar cells as substrates no longer need surface activation before being coated. Moreover, it is formulated in solution with selected additives and solvents, being suitable for the majority of common coating and printing techniques. What’s more, film thickness can be adjusted up to 10 nm, bringing savings of up to 200 % in raw materials.” Besides its use as a hole-transport material for photovoltaics, OHMIO’s new patented technology opens up a fascinating array of applications. In particular, it can be used to make transparent electrodes or antistatic coatings, enhance hole-injection layers in organic light-emitting diode displays and lighting, and serve as inks in printed electronics. Other applications include their use in windows, photographic films, construction materials, polymer capacitors and gas sensors.
OHMIO, transparent, perovskite solar cell, organic, flexible, Ohmidot, PEDOT:PSS, hole-transport, Intenanomat, conductive polymer