Ultrathin Transparent Au Electrodes for Organic Photovoltaics Fabricated Using a Mixed Mono‐Molecular Nucleation Layer

Abstract

A rapid, solvent free method for the fabrication of highly transparent ultrathin (∼8 nm) Au films on glass has been developed. This is achieved by derivatizing the glass surface with a mixed monolayer of 3‐mercaptopropyl(trim­ethoxysilane) and 3‐aminopropyl(trimethoxysilane) via co‐deposition from the vapor phase, prior to Au deposition by thermal evaporation. The mixed mono­layer modifies the growth kinetics, producing highly conductive films (∼11 Ω per square) with a remarkably low root‐mean‐square roughness (∼0.4 nm) that are exceptionally robust towards UV/O3 treatment and ultrasonic agitation in a range of common solvents. As such, they are potentially widely applicable for a variety of large area applications, particularly where stable, chemically well‐defined, ultrasmooth substrate electrodes are required, such as in organic optoelectronics and the emerging fields of nanoelectronics and nanophotonics. By integrating microsphere lithography into the fabrication process, we also demonstrate a means of tuning the transparency by incorporating a random array of circular apertures into the film. The application of these nanostructured Au electrodes is demonstrated in efficient organic photovoltaic devices where it offers a compelling alternative to indium tin oxide coated glass.

An Electrode Design Rule for Organic Photovoltaics Elucidated Using Molecular Nanolayers

“…The root-mean-square (rms) roughness of ITO glass derivatized with FPS measured using an Atomic Force Microscope (AFM) was identical to that of untreated ITO ( ∼ 3.5 nm), evidence that polymerization of FPS does not occur to any signifi cant extent using the vapor phase deposition method. This conclusion is in agreement with Aswal et al [ 34 ] and Stec et al [ 35 ] who used vapor phase deposition of trimethoxysilane nanolayers to immobilize incident Au atoms on silicon and glass substrates respectively, and is corroborated by the absence of ion fragments in the ule-SIMS spectra assigned to Si-O-Si linkages. Figure 1 (b) also shows evolution of the ϕ of UV/O 3 treated ITO glass as a function of time exposed to CPS vapor, from which it is evident that the optimal exposure time is also > 20 hrs and the ϕ of CPS derivatized ITO glass saturates at ∼ 5.25 eV.…”

Transparent electrodes for organic optoelectronic devices: a review

“…3(b)]. 103 Although there have been a few studies aimed toward increasing the electrical conductivity without sacrificing the optical transparency, 46,108,109 such as applying a seed layer to improve the continuity of thin metal layers, 110 the relatively low optical transparency of thin metals is still one of the limitations in achieving high-performance devices with them.…”

Electrohydrodynamic NanoDrip Printing of High Aspect Ratio Metal Grid Transparent Electrodes

“…Moreover, the brittleness of the ceramic ITO fi lms can present a bottleneck in the fabrication of highly fl exible devices. [ 5 ] These disadvantages have motivated recent research efforts toward alternative material systems such as carbon nanotube [ 6 ] or silver nanowire (AgNW) networks, [ 7,8 ] metallized electrospun nanowires, [ 9,10 ] graphene layers, [ 11 ] ultrathin metal fi lms, [ 12 ] self-forming [ 13 ] or patterned metal grids. [14][15][16][17][18][19][20] Ideally, besides having very good electrical and optical performance, the new system should be low cost, fl exible and include direct patterning.…”