Transparent, mixed proton/electron conducting Nafion-PEDOT:PSS composite for tandem microwire array solar water splitting devices

Abstract

One proposed integrated solar water splitting device involves two ion-exchange membrane-embedded, semiconducting micro-/nanowire arrays elec. connected as a tandem. Such an elec. connection must be optically transparent, ion permeable, and adhere to each membrane-embedded array. A composite Nafion-Poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) film possesses excellent adhesion and charge transport properties while being more transparent than PEDOT:PSS alone. Understanding the phase-sepn. behavior between conductive and non-conductive domains via PeakForce Tunneling Atomic Force Microscopy (PF-TUNA) enables insight towards the Nafion-PEDOT interactions that explain bulk elec. properties. A percolative network of conductive PEDOT domains held by a Nafion/PSS bulk enable electron conduction while maintaining the mech. stability and proton conducting properties of Nafion. Addn. of DMSO reduces these domain sizes from mm to nm scale, producing a dramatic >10^4 fold increase in lateral cond. Nanoscale current-voltage sweeps probe the spatial variations of ohmic behavior that lead to macroscale contact resistance at composite/p-Si interfaces. The measured composite properties are input into a sensitivity anal. that guides device design via load-line anal. of a model tandem water splitting device.