One thing in common with most of the emerging optoelectronic technologies is the requirement of highly transparent, conductive and flexible substrates. Emerging low-cost solar cell technologies, OLED screens, and wearable devices mainly use conductive oxides (ITO or FTO) with lower conductivity than metals. This significantly obstruct their efficiency (or increase their energetic consumption) due to the high substrate resistance that appears when the devices are scaled-up.
Metals with ultra-thin thickness (less than 10 nm), enough to allow light transmittance while keeping suitable conductivity, have been proposed as a promising technology to achieve flexible and transparent conductive substrates. Under this research line, researchers at the Gwangju Institute of Science and Technology in South Korea, have created an ultra-thin Ag film sandwiched between two polymers with outstanding properties, such as a bending radius <1 mm, a visible-range transmittance higher than 95 % and a sheet resistance lower than 10 Ω /sq. Polymer solar cells that incorporate the new electrode exhibit a high power conversion efficiency of 10 % and a fabricated polymer light-emitting diode outperform those based on existing transparent conducting oxides.
Metals with ultra-thin thickness (less than 10 nm), enough to allow light transmittance while keeping suitable conductivity, have been proposed as a promising technology to achieve flexible and transparent conductive substrates. Under this research line, researchers at the Gwangju Institute of Science and Technology in South Korea, have created an ultra-thin Ag film sandwiched between two polymers with outstanding properties, such as a bending radius <1 mm, a visible-range transmittance higher than 95 % and a sheet resistance lower than 10 Ω /sq. Polymer solar cells that incorporate the new electrode exhibit a high power conversion efficiency of 10 % and a fabricated polymer light-emitting diode outperform those based on existing transparent conducting oxides.
(Layered structure, nucleation concept and effect of the antireflecting PEDOT:PSS layer. Picture from Nature.)
The key idea to achieve this new electrodes is a novel method to produce uniform and strong metallisation points on the plastic substrates in which the nucleation centres are densely distributed over atomic-scale distances. In this way, Ag droplets were fixed on functional amine groups of a solution-processed non-conjugated polymer (polyethyleneimine). This method allows a more suitable growth of the metallic film, which previously grew forming separated islands and hence required larger thickness to interconnect them and effectively conduct electricity, which reduced the optical transmittance.
To complete the electrode, a PEDOT:PSS conducting polymer is deposited on top of the Ag film acting as anti-reflection layer, minimising the light reflection induced by the metallic Ag layer. More detailed information can be read in the article published in Nature Communications.
