Surface recombination represents a handicap for high-efficiency solar cells. This is especially important for nanowire array solar cells, where the surface-to-volume ratio is greatly enhanced. Here, the effect of different passivation materials on the effective recombination and on the device performance is experimentally analyzed. Our solar cells are large area top-down axial n-p junction silicon nanowires fabricated by means of Near-Field Phase-Shift Lithography (NF-PSL). We report an efficiency of 9.9% for the best cell, passivated with a SiO 2 /SiN x stack. The impact of the presence of a surface fixed charge density at the silicon/oxide interface is studied.

The growth of compound semiconductor nanowires on the silicon platform has opened many new perspectives in the area of electronics, optoelectronics and photovoltaics. We have grown a 1 × 1 mm 2 array of InAs nanowires on p-type silicon for the fabrication of a solar cell. Even though the nanowires are spaced by a distance of 800 nm with a 3.3% filling volume, they absorb most of the incoming light resulting in an efficiency of 1.4%. Due to the unfavourable band alignment, carrier separation at the junction is poor. Photocurrent increases sharply at the surrounding edge with the silicon, where the nanowires do not absorb anymore. This is further proof of the enhanced absorption of semiconductors in nanowire form. This work brings further elements in the design of nanowire-based solar cells.

We report on the impact of the doping concentration design on the performance of silicon microwire arrays as photovoltaic devices. We have fabricated arrays with different p-and ndoping profiles and thicknesses, obtaining mean efficiencies as high as 9.7% under AM 1.5G solar illumination. The results reveal the importance of scaling the microwire diameter with the depletion width resulting from doping concentrations. The doping of the core should be kept low in order to reduce bulk recombination. Furthermore, the thickness of the n-shell should be kept as thin as possible to limit the emitter losses.

Semiconductor nanowires are currently at the forefront of research in the areas of nanoelectronics and energy conversion. In all these studies, realising electrical contacts and statistically relevant measurements is a key issue. We propose a method that enables to contact hundreds of nanowires on a single wafer in an extremely fast electron beam lithography session. The method is applied to nanowire-based radial GaAs p-i-n junction. Currentvoltage characteristics are shown, along with scanning photocurrent mapping.

3958 wileyonlinelibrary.com conformal manner. [ 8 ] Conductive oxides such as ZnO or ITO are one attractive possibility. However, while ITO can be deposited in a relatively conformal manner on nanowires, the scarcity of indium in the earth crust has led researchers to seek alternative solutions. Such alternatives include graphene, [ 9 ] carbon nanotubes, [ 10,11 ] conductive polymers, [ 12,13 ] nanocellulose fi ber papers [ 14 ] or metal nanowire mesh. [15][16][17][18] While metal nanoarchitectures are potentially interesting electrode materials, their application on complex surfaces, such as, e.g., 3D structured solar cells, is a challenge. This contribution presents a scalable process that allows to fabricate silicon microwire-based solar cells modifi ed with a highly conformal silver or gold nanoparticle fi lm. It will be shown that these metal nanoparticle coatings perform a dual function and not only act as a conductive electrode layer but also enhance light capture due to the fact that the metal nanoparticles behave as plasmonic scattering elements. [19][20][21] The proposed process is outlined in Figure 1 and uses an ultrathin coating consisting of densely grafted polymer chains, which are tethered with one chain end to the surface, to guide the formation of a metal nanoparticle-based electrode layer. These surface-grafted polymer fi lms are often colloquially referred to as "polymer brushes." Polymer brush coatings can be fabricated in a bottom-up fashion via surface-initiated polymerization [ 22 ] and have already been successfully used as templates for the fabrication of thin inorganic [23][24][25][26] and metallic fi lms. [ 27 ] Surfaceinitiated polymerizations are attractive in that they allow to control the thickness of the metal nanoparticle fi lm by controlling the polymer brush thickness and are also compatible with photopatterning strategies, which potentially could allow access to microstructured metal nanoparticle coatings. Furthermore, being a bottom-up strategy, surface-initiated polymerizations also allow facile and controlled deposition of thin, conformal polymer coatings on complex, 3D structured substrates, such as, e.g., nano-or microwires or nano-or microporous materials, which is challenging to achieve using more conventional polymer fi lm forming methods such as spin-or drop-casting. The fabrication of the metal nanoparticle-based electrodes starts with modifi cation of the solar cell surface with an appropriate polymerization initiator, followed by surface-initiated polymerization to generate a thin polymer brush fi lm (Figure 1 ). In the present work, atom transfer radical polymerization (ATRP) was used to grow the polymer brushes. After that, the polymer This report explores the use of sacrifi cial thin polymer fi lms prepared by surface-initiated polymerization as a template for the fabrication of highly conformal metal nanoparticle solar cell electrodes. As a fi rst proof-of-principle, the use of this method is demonstrated to prepare top electrodes on planar and microwire-based ...