Takaaki Chiba

Direct and Dry Deposited Single-Walled Carbon Nanotube Films Doped with MoOx as Electron-Blocking Transparent Electrodes for Flexible Organic Solar Cells

UNLABELLED Organic solar cells have been regarded as a promising electrical energy source. Transparent and conductive carbon nanotube film offers an alternative to commonly used ITO in photovoltaics with superior flexibility. This communication reports carbon nanotube-based indium-free organic solar cells and their flexible application. Direct and dry deposited carbon nanotube film doped with MoO(x) functions as an electron-blocking transparent electrode, and its performance is enhanced further by overcoating with PEDOT PSS. The single-walled carbon nanotube organic solar cell in this work shows a power conversion efficiency of 6.04%. This value is 83% of the leading ITO-based device performance (7.48%). Flexible application shows 3.91% efficiency and is capable of withstanding a severe cyclic flex test.

Air-stable high-efficiency solar cells with dry-transferred single-walled carbon nanotube films

By using the excellent optical and electrical properties of pristine SWNTs with long bundle lengths, we present single-walled carbon nanotube–silicon (SWNT/Si) solar cells of 11% power conversion efficiency (PCE), prepared without doping. The PCEs of the fabricated solar cells even increased slightly after 10 months of exposure to ambient conditions, without any external protection. The open-circuit voltage of the SWNT/Si solar cells under low light intensities, down to 10 mW cm−2, demonstrated the characteristics of the ideal p–n junction model. The mechanism was discussed, taking into account the effect of varying the interfacial oxide layer thickness between the SWNTs and Si on the solar cell’s performance. The high efficiency and stability demonstrated in this study make SWNT/Si solar cells one of practical choices for next generation energy system.

SELF-ORGANIZED MICRO-HONEYCOMB NETWORK STRUCTURE OF SINGLE-WALLED CARBON NANOTUBES FOR PHOTOVOLTAIC DEVICES

Single-walled carbon nanotubes (SWNTs) are expected to be a promising nanomaterial because of their outstanding electronic, mechanical, and thermal properties. For macroscopic device applications, an assembly of SWNTs is a critical issue. We propose a self-organized micro-honeycomb network structure of SWNTs obtained by water vapor treatment of as-synthesized vertically-aligned SWNTs (VA-SWNT) for solar cell devices with higher performance. The micro-honeycomb structure was realized by simply exposing VA-SWNT to water vapor and drying in ambient condition. Honeycomb cell walls consist of capillary-aggregated vertically aligned SWNTs with heavily bundled top part. Within each cell, collapsed spaghetti-like SWNTs make contact to the substrate. The SWNT/n-Si heterojunction solar cell was built by placing the micro-honeycomb SWNTs network film on top of the substrate which has a 3 mm × 3 mm bare n-type silicon contact window in the center. The contact window is surrounded by SiO2 as insulating layer and Pt as electrode. Our preliminary tests showed that optimal photovoltaic conversion efficiency (PCE) under AM1.5 was 5.91%, with the fill factor of 72%. The open-circuit voltage and short-circuit current are 0.53V and 15.5 mA/cm2, respectively. This showed a substantial improvement compared with heterojunction solar cells using spaghetti-like SWNTs. Furthermore, the superior performance of dye-sensitized solar cells with the micro-honeycomb SWNTs was demonstrated.Copyright