Hare Ram Aryal

Silicon nanowire array/polymer hybrid solar cell incorporating carbon nanotubes

Here we present a simple and novel approach of fabricating three dimensional (3D) n-Si nanowires (NWs) and poly(3-octylthiophene) hybrid solar cells incorporating carbon nanotubes (CNTs). Vertically aligned n-Si NWs arrays were fabricated by electroless chemical etching of a n-Si [1?1?1] wafer. n-Si NWs/poly(3-octylthiophene) hybrid solar cells were fabricated with and without functionalized CNTs incorporation. Fabricated solar cells incorporating CNTs show open circuit voltage (Voc), short circuit current density (Jsc) fill factor (FF) and conversion efficiency as 0.353, 7.85?mA?cm?2, 22% and 0.61%, respectively. In fabricated devices n-Si NWs arrays form multiple heterojunctions with the polymer and provide efficient electron collection and transportation, whereas CNTs provide efficient hole transportation.

Improving photovoltaic properties by incorporating both single walled carbon nanotubes and functionalized multiwalled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) and functionalized multiwalled carbon nanotubes (f-MWCNTs) are introduced together for photovoltaic application in a poly(3-octylthiophene)/n-Si heterojunction solar cell. The performance of the device was improved by manyfold by the incorporation of both SWCNTs and f-MWCNTs. The open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF), and power conversion efficiency (η) were 0.44 V, 6.16 mA/cm2, 36%, and 0.98%, respectively. Here, we expect that SWCNTs help in exciton dissociation and provide percolation paths for electron transfer, whereas f-MWCNTs provide efficient hole transportation. CNT incorporation yields better carrier mobility, easy exciton splitting, and suppression of charge recombination, thereby improving photovoltaic action.

Fullerene (C60) decoration in oxygen plasma treated multiwalled carbon nanotubes for photovoltaic application

Multiwalled carbon nanotubes (MWNTs) were functionalized by oxygen plasma treatment. Photoelectron spectroscopy study of oxygen plasma treated MWNTs (O-MWNTs) shows surface modification with hydroxyl and carboxyl groups. C60 decoration of MWNTs were carried out by thermal evaporation and more dense distribution of C60 was achieved on O-MWNTs. C60 decorated MWNTs were combined with poly(3-octylthiophene) for photovoltaic device fabrication. The device with C60 decorated O-MWNTs shows short circuit current density (Jsc), open circuit voltage (Voc), fill factor, and power conversion efficiency (η) as 1.68mA∕cm2, 0.245V, 27%, and 0.11%, respectively. It is expected that C60 provide large surface area for photoexcitons dissociation and efficient electron transportation, whereas MWNTs provide efficient hole transportation.

Cutting carbon nanotubes for solar cell application

This paper presents the application of cutting multiwalled carbon nanotubes (cut-MWNTs) in solar cell. Cutting of MWNTs is performed by plasma fluorination and followed by defluorination. Cut-MWNTs with lengths of 50–200nm are incorporated in a poly(3-octylthiophene)∕n-Si heterojunction solar cell. We found that a device fabricated with cut-MWNTs shows much better performance than that of a device with pristine MWNTs. The device with cut-MWNTs shows short circuit current density, open circuit voltage, fill factor, and power conversion efficiency as 7.65mA∕cm2, 0.23V, 31%, and 0.54%, respectively. Here, we proposed that cut-MWNTs provide efficient hole transportation having a few nanometer transportation path, hence suppressing recombination. Cut-MWNTs can be the solution to the shorting and shunting effects generally observed in the MWNT solar cell.

Few layers isolated graphene domains grown on copper foils by microwave surface wave plasma CVD using camphor as a precursor

Few layers isolated graphene domains were grown by microwave surface wave plasma CVD technique using camphor at low temperature. Graphene nucleation centers were suppressed on pre-annealed copper foils by supplying low dissociation energy. Scanning electron microscopy study of time dependent growth reveals that graphene nucleation centers were preciously suppressed, which indicates the possibility of controlled growth of large area single crystal graphene domains by plasma processing. Raman spectroscopy revealed that the graphene domains are few layered which consist of relatively low defects.

Some aspects of nitrogen doped amorphous carbon thin films

Optical, structural and photovoltaic properties of amorphous carbon (a-C) thin films deposited on p-type silicon (p-Si) and quartz substrates by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD) were analyzed in this paper. Argon (Ar: 200 sccm) was used as carrier gas while acetylene (C2H2: 20 sccm) and nitrogen (N: 0 and 10 sccm) were used as plasma source. Analytical methods such as X-ray photoelectron spectroscopy (XPS), Raman and UV-visible spectroscopy were employed to investigate the structural and optical properties of the a-C thin films respectively. The optical gaps of the films were tailored from 1.2 eV to 0.9 eV with nitrogen doping. Nitrogen doped a-C (a-C:N) thin film showed the photoconductivity action under white light illumination and hence Au/a-C:N/p-Si/Au heterojunction solar cell was fabricated with 0.23 V open circuit voltage, fill factor 25 and efficiency 5.7* 10−3 %.

Photovoltaic Properties of a-C:N/p-Si Heterojunction Solar Cell Synthesized by Microwave Surface Wave Plasma CVD

Amorphous carbon (a-C) thin films have been synthesized by microwave surface wave plasma chemical vapor deposition at low temperature (<100 degC). The influence of nitrogen doping on the properties a-C films is reported. Argon, acetylene and nitrogen (N) were used as a carrier, source and dopant gases. Analytical methods such as X-ray photoelectron spectroscopy (XPS), Nanopics 2100/NPX200 surface profiler, JASCO V-570 UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and Solar simulator were employed to investigate chemical, optical, structural and electrical properties of the films. Successfully nitrogen incorporated (29.37 at. %) into the film was found. The optical band gaps decreased from 2.7 to 1.7 eV. The photovoltaic measurements of a-C:N/p-Si structure show that the open-circuit voltage (Voc) of 4.7 mV and a short-circuit current density (Jsc) of 19.6 muA/cm2 under light illumination (AM 1.5 100 mW/cm2). The energy conversion efficiency and fill factor of the solar cell were found to be 2.24times10-4 % and 0.24 respectively

Compositional and structural variations of nitrogen doped amorphous carbon films grown by surface-wave mode microwave plasma CVD

In this paper, we report the effect of acetylene (C<inf>2</inf>H<inf>2</inf>) flow rates (5 to 20 sccm) on the compositional and structural variations of nitrogen doped amorphous carbon (a-C:N) thin films grown by surface-wave mode microwave plasma chemical vapor deposition at low temperature (≪100 °C). Argon was used as the main plasma source gas. The films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV/VIS/NIR spectroscopy and Fourier transform infrared spectroscopy (FTIR) measurements. The deposition rate of the films was typically 10 nm/min. The Tauc optical band gap of the films was in the range 1.6–1.8 eV. The XPS results show successful doping of nitrogen in the films, whereas N atomic concentration (at.%) into the films varied in the range of 23 to 35%. The N at.% in the films did not correlate with the increase of C<inf>2</inf>H<inf>2</inf> flow rate (i.e. decrease of nitrogen gas concentration). The maximum percentage of nitrogen take up was observed in the film grown at C<inf>2</inf>H<inf>2</inf> flow rate of 10 sccm. The FTIR results show enhanced contribution of C=C sp² and C-N sp³ bonds with increasing C<inf>2</inf>H<inf>2</inf> flow rate. The increase of C-H vibration mode around 3300 cm⁻¹ indicates the increase of sp³-bonded carbon in the films. The amorphous nature of the films was qualitatively understood from the Raman results.

Carbon nano materials (CNMs) for photovoltaic device application

Here, we present application of functionalized multiwalled carbon nanotubes (MWNTs) in hetrojunction photovoltaic devices. Functionalization of MWNTs were achieved by Surface wave microwave (SW-MW) plasma treatment. MWNTs were treated with nitrogen (N2) plasma in order to functionalize covalently their side walls with nitrogen functional groups. Functionalized CNTs were incorporated in heterojunction photovoltaic device along with poly-(3-octylthiophene) (P3OT). Fabricated device incorporating MWNTs, with the structure Au/P3OT+MWNTs/n-Si shows power conversion efficiency (η) of 0.086%. Functionalized MWNTs were incorporated in fullerene (C60)/P3OT heterojunction solar cell. It was observed that with incorporation of MWNTs there are significant improvement of device performance. With incorporation of functionalized MWNTs there can be easy exciton dissociation as well as better hole transportation along the length of nanotubes.

Effect of process parameters on the properties of diamond like carbon films deposition by microwave surface-wave plasma CVD

Diamond like carbon (DLC) thin films were deposited on various substrates, such as, silicon, quartz and ITO substrates at low temperature (≪100 °C) by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD), for solar cell application. The methane (CH4), ethylene (C2H4) and acetylene (C2H2) were used as carbon precursors, while argon was used as carrier gas. Nitrogen is used as dopant. The deposited DLC films were characterized by UV/VIS/NIR spectrophotometer, Raman, FT-IR and XPS measurements. In this paper, we report some experimental results of the optical and structural properties of the films; the results suggested that it is possible to control film growth rate and optical band gap, and consequently improve photoconductivity by proper selection of deposition parameters, optimizing dopants and appropriate deposition temperature. Our research work can be realize cheap, reasonably environmentally friendly and high efficiency solar cell.