Tuning, optimization, and perovskite solar cell device integration of ultrathin poly(3,4-ethylene dioxythiophene) films via a single-step all-dry process.

For semicrystalline poly(3,4-ethylene dioxythiophene) (PEDOT), oxidative chemical vapor deposition (oCVD) enables systematic control over the b-axis lattice parameter (π-π stacking distance). Decreasing the b-axis lattice parameter increases the charge transfer integral, thus enhancing intracrystallite mobility. To reduce the barrier to intercrystallite transport, oCVD conditions were tailored to produce pure face-on crystallite orientation rather than the more common edge-on orientation. The face-on oriented oCVD PEDOT with the lowest b-axis lattice parameter displayed the highest in-plane electrical conductivity (σdc = 2800 S/cm), largest optical bandgap (2.9 eV), and lowest degree of disorder as characterized by the Urbach band edge energy. With the single step oCVD process at growth conditions compatible with direct deposition onto flexible plastic substrates, the ratio σdc/σop reached 50. As compared to spun-cast PEDOT:polystyrene sulfonate, integration of oCVD PEDOT as a hole transport layer (HTL) improved both the power conversion efficiency (PCE) and shelf-life stability of inverted perovskite solar cells (PSC).

An Electrochemical Reaction-Diffusion Model of the Photocatalytic Effect of Photosystem I Multilayer Films.

The photosynthetic protein, photosystem I (PSI), has been used as a photoactive species within a host of biohybrid photoelectrochemical systems. PSI multilayer films at electrode surfaces provide greatly improved solar energy conversion relative to homologous monolayer films. While the photocatalytic effect of PSI multilayers has been theorized as an electrolyte-mediated mechanism, no comprehensive, first-principles modeling study has been presented. In this work, we develop and optimize an electrochemical reaction-diffusion model to replicate the significant electrochemical, physicochemical, and transport processes that underpin photocurrent development of a PSI multilayer film. We use this model to provide strong evidence that PSI's terminal cofactors rapidly exchange electrons with diffusible mediators and stimulate photocurrent principally due to alteration of mediator concentrations at a solution-electrode interface as governed by Butler-Volmer kinetics. Our fitted model accurately replicates photocurrent trends under a variety of conditions, including variable applied bias and PSI multilayer film thickness.