Electrochemical polymerization of PEDOT on catalyst-free patterned GaAs nanopillars for high efficiency hybrid photovoltaics 37th IEEE photovoltaic specialists conference

In this work, we present hybrid nanostructured core-shell solar cells based on patterned GaAs nanopillars grown by MOCVD, coated with electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT) polymer. The patterns are photolithographically defined and center-to-center pitch, hole size and mask arrangement can be precisely predetermined at nanometric resolution. Our inherently catalyst-free growth mode eliminates any metal (i.e. Au) diffusion into the nanopillars that could hinder the electron-hole pair extraction, paramount in photovoltaics. Hybrid devices [1-3] are normally obtained by spin-coating conjugated polymers on top of inorganic semiconducting surfaces. Spin-coating techniques allow to achieve only non-conformal thin films on planar substrates, yet it offers scarce controllability for 3-D structures where the polymer needs to be coated uniformly along the sides of the nanostructures too. Electrolytic deposition approaches, on the other hand, offer a simple, versatile route to high quality, conformal coatings to conductive surfaces regardless of the device structure. In addition, it possesses exquisite selectivity over the deposition position and precise control of the coating thickness and morphology, representing an attractive technique for fabricating core-shell inorganic-organic structured devices. This study demonstrates the rational design of a hybrid photovoltaic device through the careful tuning of the thickness, morphology, and physical/chemical properties of the polymer layer by electrodeposition, in conjunction with the manipulation over the size and properties of the patterned GaAs nanopillar arrays via MOCVD, in order to achieve optimized device configuration and performance. Device characterization is carried out in terms of photocurrent density-voltage (J-V) characteristics (under dark and standard AM 1.5 conditions), external quantum efficiency (EQE), and transient open-circuit voltage decay (TOCVD), standard figures of merit in the photovoltaic field.