Stable ultrathin surfactant-free surface-engineered silicon nanocrystal solar cells deposited at room temperature

We present a scalable technology at room temperature for the fabrication of ultrathin films based on surfactant-free surface-engineered silicon nanocrystals (SiNCs). Environmentally friendly pulsed fsec laser induced surface engineering of SiNCs and vacuum low-angle spray deposition is used to produce ultrathin films. Surface engineering of SiNCs improved stability and dispersibility of SiNCs by allowing thin (30 nm thickness) and exceptionally smooth (mean square roughness corresponds to 0.32 nm) film deposition at room temperature. The quality of the SiNC thin films is confirmed by ultrafast photoluminescence measurements and by applying such films for solar cells. We demonstrate that films produced with this approach yield good and stable devices. The methodology developed here is highly relevant for a very wide range of applications where the formation of high-quality ultrathin films of quantum dots with controllable thickness and smoothness is required

Structural modifications of zinc phthalocyanine thin films for organic photovoltaic applications

Zinc phthalocyanine (ZnPc) thin films are vacuum-evaporated on bare indium-tin-oxide (ITO) coated glass by varying substrate temperature and growth rate. The samples are characterized by atomic force microscopy, x-ray diffraction, and infrared spectroscopy. The temperature does not play a clear role in the crystalline growth of ZnPc possibly due to the significant structural defects on ITO surface, while it strongly influences the surface morphology and molecular alignment. The relationships between growth characteristics and performances of photovoltaics with planar heterojunction are discussed in detail. Increasing temperature or growth rate leads to a rougher surface morphology, which enables more donor/accepter interface area for photocurrent generation. Moreover, at elevated temperature, more molecules adopt standing-up geometry, resulting in a reduction in overall efficiency. The results imply that low-temperature process in order to control the molecular alignment is preferred for efficient organic photovoltaics. By simply increasing the growth rate of ZnPc up to 0.40 Å/s at room temperature, ZnPc/C60 planar heterojunction shows an efficiency of 1.66, compared to 1.24 for the cell when ZnPc is prepared at 0.10 Å/s. © 2012 American Institute of Physics

"Phase separation of co-evaporated ZnPc:C

We demonstrate phase separation of co-evaporated zinc phthalocyanine (ZnPc) and fullerene (C 60) for efficient organic photovoltaic cells. With introducing a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film and a crystalline copper iodide film on indium tin oxide, 20-nm-thick ZnPc film adopts a lying-down crystalline geometry with grain sizes of about 50 nm. This surface distributed with strong interaction areas and weak interaction areas enables the selective growth of ZnPc and C 60 molecules during following co-evaporation, which not only results in a phase separation but also improve the crystalline growth of C 60. This blend film greatly enhances the efficiencies in photocurrent generation and carrier transport, resulting in a high power conversion efficiency of 4.56 under 1 sun. © 2012 American Institute of Physics

Stability of silicon–tin alloyed nanocrystals with high tin concentration synthesized by femtosecond laser plasma in liquid media

Nanocrystals have a great potential for future materials with tunable bandgap, due to their optical properties that are related with the material used, their sizes and their surface termination. Here, we concentrate on the silicon–tin alloy for photovoltaic applications due to their bandgap, lower than bulk Si, and also the possibility to activate direct band to band transition for high tin concentration. We synthesized silicon–tin alloy nanocrystals (SiSn-NCs) with diameter of about 2–3 nm by confined plasma technique employing a femtosecond laser irradiation on amorphous silicon–tin substrate submerged in liquid media. The tin concentration is estimated to be ∼ 17 % , being the highest Sn concentration for SiSn-NCs reported so far. Our SiSn-NCs have a well-defined zinc-blend structure and, contrary to pure tin NCs, also an excellent thermal stability comparable to highly stable silicon NCs. We demonstrate by means of high resolution synchrotron XRD analysis (SPring 8) that the SiSn-NCs remain stable from room temperature up to 400∘C, with a relatively small expansion of the crystal lattice. The high thermal stability observed experimentally is rationalized by means of first-principle calculations

<Chapter 14> Does Green Supply Chain Management enhance environmental management capacity? A case of the machinery industry in Japan and China (Part V: Hybrid systems in environmental governance)

Edited by Akihisa Mor