The ability to pattern porous materials with functional polymeric coatings is important for the fabrication of next-generation microfluidic platforms, membranes, tissue scaffolds, and optical devices. Here, we demonstrate for the first time that solventless initiated chemical vapor deposition (iCVD) can be used for three-dimensional patterning of porous substrates. The individual fibers of hydrophilic chromatography paper were uniformly coated with a thin layer of hydrophobic photoresponsive poly(o-nitrobenzyl methacrylate) (PoNBMA). X-Ray photoelectron spectroscopy and contact angle measurements confirmed that the PoNBMA coating penetrated the entire depth of the paper and scanning electron microscope images confirmed that the porosity and hierarchical structure of the paper were retained during the coating process. The PoNBMA coating was then patterned through the entire depth of the paper by exposure to ultraviolet light followed by rinsing in biologically compatible buffer. We demonstrated the utility of our patterning process by fabricating three-dimensional hydrophilic and hydrophobic regions into the chromatography paper for use as paper-based microfluidic devices. Our patterning process represents an environmentally friendly method to pattern three-dimensional materials since no organic solvents are used during the polymerization process or patterning step.

This paper demonstrates the ability to control the location of polymer deposition onto porous substrates using vapor phase polymerization in combination with metal salt inhibitors. Functional polymers such as hydrophobic poly(1H,1H,2H,2H-perfluorodecyl acrylate), click-active poly(pentafluorophenyl methacrylate), and light-responsive poly(ortho-nitrobenzyl methacrylate) were patterned onto porous hydrophilic substrates using metal salts. A combinatorial screening approach was used to determine the effects of different transition metal salts and reaction parameters on the patterning process. It was found that CuCl2 and Cu(NO3)2 were effective at uniformly inhibiting the deposition of all three polymers through the depth of the porous substrate and along the entire cross section. This study offers a new and convenient method to selectively deposit a wide variety of functional polymers onto porous materials and will enable the production of next-generation multifunctional paper-based microfluidic devices, polymeric photonic crystals, and filtration membranes.

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A wide variety of photovoltaic cell technologies have shown dramatic performance improvements over the past decade, yet the prospect of a practical module capable of 50% efficiency remains remote. Experimentally achieved singlecell devices have achieved a record efficiency of 28.8% [1], which is close to the theoretical limit of 33.8% for such devices [2]. However, the single-cell limit is far below the fundamental efficiency limit for solar energy conversion of 74.0% for global illumination and 92.8% for direct [2] because a single pn junction can only efficiently convert photons with energy close to the value of its energy bandgap. The best single junction cell will lose more than 40% of the energy in the incident light to transmission of subbandgap photons and thermalization of carriers with photon energy in excess of the bandgap [3]. Spectrum splitting, which divides the solar spectrum into spectral bands of different energy and directs the bands onto multiple subcells with bandgap values matched to the energy of their photon allocation, is a necessary feature of any photovoltaic design capable of achieving >33.8% efficiency. The use of multiple subcells to increase conversion efficiency is well known. In these designs, the subcells are grown monolithically in a stacked configuration and are electrically in series. The incident spectrum is divided among the subcells by sequential absorption, with the top subcells absorbing and converting high energy photons

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