http://depts.washington.edu/solgel/documents/pub_docs/journal_docs/2011/Nanostructured%20carbon%20for%20energy%20storage%20and%20conversion.pdf

Nanostructured carbon for energy storage and conversion

Transparent conducting films (TCFs) are a critical component in many personal electronic devices. Transparent and conductive doped metal oxides are widely used in industry due to their excellent optoelectronic properties as well as the mature understanding of their production and handling. However, they are not compatible with future flexible electronics developments where large-scale production will likely involve roll-to-roll manufacturing. Recent studies have shown that carbon nanotubes provide unique chemical, physical, and optoelectronic properties, making them an important alternative to doped metal oxides. This Review provides a comprehensive analysis of carbon nanotube transparent conductive films covering detailed fabrication methods including patterning of the films, chemical doping effects, and hybridization with other materials. There is a focus on optoelectronic properties of the films and potential in applications such as photovoltaics, touch panels, liquid crystal displays, and organic light-emitting diodes in conjunction with a critical analysis of both the merits and shortcomings of carbon nanotube transparent conductive films.

Recent Development of Carbon Nanotube Transparent Conductive Films

Schottky junction solar cells are assembled by directly coating graphene films on n-type silicon nanowire (SiNW) arrays. The graphene/SiNW junction shows enhanced light trapping and faster carrier transport compared to the graphene/planar Si structure. With chemical doping, the SiNW-based solar cells showed energy conversion efficiencies of up to 2.86% at AM1.5 condition, opening a possibility of using graphene/semiconductor nanostructures in photovoltaic application.

Graphene/Silicon Nanowire Schottky Junction for Enhanced Light Harvesting

Carrier transport characteristics in high-efficiency single-walled carbon nanotubes (SWNTs)/silicon (Si) hybrid solar cells are presented. The solar cells were fabricated by depositing intrinsic p-type SWNT thin-films on n-type Si wafers without involving any high-temperature process for p–n junction formation. The optimized cells showed a device ideality factor close to unity and a record-high power-conversion-efficiency of >11%. By investigating the dark forward current density characteristics with varying temperature, we have identified that the temperature-dependent current rectification originates from the thermally activated band-to-band transition of carriers in Si, and the role of the SWNT thin films is to establish a built-in potential for carrier separation/collection. We have also established that the dominant carrier transport mechanism is diffusion, with minimal interface recombination. This is further supported by the observation of a long minority carrier lifetime of ∼34 μs, determined by t...

Record High Efficiency Single-Walled Carbon Nanotube/Silicon p-n Junction Solar Cells

A facile chemical approach has been developed to produce nanohybrids with ultrathin Co oxides nanowall arrays on reduced graphene oxide (rGO) sheets. The Co oxides exhibited porous structure. The porosity of the Co oxide/rGO nanohybrids and the grain size of the Co oxides could be tailored by varying the annealing temperature, which directly affected their performance as Li-ion battery electrodes. When tested as anode materials for Li-ion batteries, these Co oxide/rGO nanohybrids showed structural-process-dependent performances. For example, Co3O4/rGO hybrids obtained by annealing α-Co(OH)2/rGO at 350 °C showed a high specific capacity of 673 mAh g−1 after 100 cycles at a discharge current density of 180 mA g−1 (0.2 C), which was better than Co3O4/rGO samples obtained at other annealing temperatures. Similarly, CoO/rGO hybrids obtained by pyrolysis of α-Co(OH)2/rGO at 350 °C showed optimum performance, as compared to that of CoO/rGO samples obtained at other annealing temperatures, with a capacity of 732 ...

Cobalt Oxide Nanowall Arrays on Reduced Graphene Oxide Sheets with Controlled Phase, Grain Size, and Porosity for Li-Ion Battery Electrodes

We report a metal-insulator-semiconductor heterojunction solar cell by depositing a carbon nanotube film onto silicon substrate, followed by acid oxidation of the Si surface to form a thin oxide layer at the junction interface. The nanotube-oxide-Si solar cells with polymer encapsulation show stable efficiencies of above 10%, owing to enhanced photon absorption, inhibited charge recombination, and reduced internal resistance. Parallel and series connections without sacrificing cell efficiencies were demonstrated.

Encapsulated carbon nanotube-oxide-silicon solar cells with stable 10% efficiency

Efficient energy conversion of nanotube/nanowire-based solar cells

A novel method of combining photolithography, wet chemical etching and oxidation process was proposed to fabricate large area of silicon microwire (SiMW) arrays. The dimensions of the SiMWs can be easily controlled by photomask and etching conditions. Solar cells based on the heterojunction between SiMW and double-walled carbon nanotubes (DWNTs) were constructed. The initial test on the DWNT/SiMW shows efficiency (η) of 0.59%. By adding a few drops of HBr/B2 electrolyte, the efficiency was improved to 1.96% with Jsc=19.2 mA/cm2 and Voc=0.35 V, FF=29.2%, showing the potential of SiMWs in photovoltaic applications.

Fabrication of silicon microwire arrays for photovoltaic applications

High-efficiency micro core–shell solar cell (μ-CSSC) arrays are fabricated from Si wafer by using traditional lithography and phosphorus diffusion. The p–n junction depth is around 450 nm, indicating that it forms core–shell structure in micropillars by using phosphorus diffusion. The μ-CSSC arrays have high minority carrier lifetime of 23 μs and long diffusion length of ∼150 μm. The best power efficiency of the μ-CSSC reaches to 9.2%. It is a convenient method for fabricating Si μ-CSSC arrays in wafer scale for future applications.

High-efficiency core-shell solar cell array from Si wafer

The invention discloses a phosphorus-doped core-shell type structural solar cell based on silicon line arrays and a fabrication method thereof, belonging to the technical field of application of silicon material devices, micron materials and solar cells. The core-shell type solar cell comprises silicon line arrays, wherein the side length or the diameter and the height of the silicon line arrays are in micron dimensions, and the space between silicon lines is adjustable and controllable; each silicon line array has the advantages of regular appearance, smooth surface, even height, better light absorption efficiency, and the like. In the silicon line array, a core-shell type structure with an outer surface of a phosphorus-doped silicon layer (in an N type) and a core of a P type silicon layer is prepared from P type silicon through a phosphorus-doped technology to realize the structure that one million of micron solar cells are distributed on an area of 1*2cm in parallel. In the phosphorus-doped technology, the thickness of the phosphorus-doped layer is controlled by controlling a volume ratio of blasted nitrogen to blasted oxygen, phosphorus-doped temperature, phosphorus-doped time, and the like; and the cell conversion efficiency reaches 9.22 percent.

Ying Xu

Papers

Encapsulated carbon nanotube-oxide-silicon solar cells with stable 10% efficiency

Efficient energy conversion of nanotube/nanowire-based solar cells

Fabrication of silicon microwire arrays for photovoltaic applications

High-efficiency core-shell solar cell array from Si wafer

Phosphorus-doped core-shell type structural solar cell based on silicon line arrays and fabrication method thereof