Fabrication of Copper Window Electrodes with ≈10⁸ Apertures cm⁻² for Organic Photovoltaics

Abstract

A powerful approach to increasing the far-field transparency of copper film window electrodes which simultaneously reduces intraband absorption losses for wavelengths <550 nm and suppresses reflective losses for wavelengths >550 nm is reported. The approach is based on incorporation of a random array of ≈100 million circular apertures per cm 2 into an optically thin copper film, with a mean aperture diameter of ≈500 nm. A method for the fabrication of these electrodes is described that exploits a binary polymer blend mask that self-organizes at room temperature from a single solution, and so is simple to implement. Additionally all of the materials used in electrode fabrication are low cost, low toxicity, and widely available. It is shown that these nanostructured copper electrodes offer an average far-field transparency of ≥80% and sheet resistance of ≤10 Ω sq −1 when used in conjunction with a conventional solution processed ZnO electron transport layer and their utility in inverted organic photovoltaic devices is demonstrated.

An Electrode Design Rule for Organic Photovoltaics Elucidated Using a Low Surface Area Electrode

“…Many high performance OPVs use selective charge transport layers with conductivity substantially higher than that of MoO3-x, which enables their thickness to be increased so they can also serve as optical spacers [21] . The most widely used electron-selective layer is ZnO which is typically used with a thickness in the range 30-70 nm [22] . When deposited from a colloidal solution with low temperature annealing, as in this case, the conductivity of ZnO is at least an order of magnitude higher than evaporated MoO3-x, although is still very resistive [23] , as is evident from the current map in Figure 7a recorded using a c-AFM.…”

Enhanced Oxidation Stability of Transparent Copper Films Using a Hybrid Organic‐Inorganic Nucleation Layer

“…[11][12][13] It has also been shown that the higher optical losses in Cu, as compared to Ag, can be mitigated by electrode and/or device design, including using a metal oxide overlayer to increase transparency. [14][15][16] Due to the high surface energy of Cu and Ag these metals interact only weakly with glass and other technologically important transparent plastic substrates, such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), and so the formation of robust and continuous films of these metals with thickness < 10 nm is notoriously difficult to achieve using thermal evaporation. [3,17] Metal atoms condensing on the substrate diffuse over the surface and aggregate into particles which only form a continuous network for nominal thicknesses > 10 nm.…”

“…In recent years copper (Cu) has received growing attention as a low cost alternative to Ag for window electrode applications because it has an electrical conductivity comparable to Ag at ∼1% of the cost . It has also been shown that the higher optical losses in Cu, as compared to Ag, can be mitigated by electrode and/or device design, including using a metal oxide overlayer to increase transparency …”

Development of Highly Bendable Transparent Window Electrodes Based on MoOx, SnO2, and Au Dielectric/Metal/Dielectric Stacks: Application to Indium Tin Oxide (ITO)-Free Perovskite Solar Cells

“…Attractive alternatives to conventional TCOs are represented by metallic nanostructures in the form of ultrathin films (Stec et al, 2011;Zhang et al, 2017;Pereira et al, 2018) or multilayered structural configurations, such as dielectric/metal/dielectric (D/M/D), organic/metal/organic and polymer/metal/polymer architectures (Cattin et al, 2013;Della Gaspera et al, 2015;Guo et al, 2015;Aleksandrova et al, 2016;Kao et al, 2018;Liang et al, 2018). D/M/D are excellent candidates as transparent conductors (Bi et al, 2019): in general stacks based on Ag ultrathin films show the best optoelectrical properties (T = 80-90%, R s = 10-20 /sq) (Guo et al, 2012;Wang et al, 2014;Behrendt et al, 2015), but multilayers based on Au should be preferred for application in PSCs, due to their higher stability.…”