In this paper, we report a first hand study of plasmon-enhanced photocurrent observed in hybrid nanostructures based heterojunction solar cell. The heterojunction solar cell was fabricated, using chemically synthesized narrow gap, IV-VI group semiconductor nanoparticles (PbS) of 3∼6nm diameter, wide gap semiconductor ZnO nanowires of 500nm∼1 μm length and ∼50nm diameter, and gold nanoparticles (∼5nm to 30nm), by spin-coating (∼20cycles) onto FTO glasses, in ambient conditions (25°C, 1atm). The synthesized nanostructures were characterized by XRD, UV-VIS absorption, SEM, TEM, solar simulator, etc. Nanostructures of variant sizes were integrated in to the heterojunction devices to study the effects on photocurrent and solar cell performance. The sizes, lengths, thickness of nanostructures were optimized to have best solar cell devices. The effects of fabrication conditions (such as growth temperature, growth time, anneal temperature, ligand treatments, in air or in N2, etc.) on device performance were also studied. The architecture of film stack, i.e., the positions of Au nanoparticles and PbS nanoparticles were also studied. It was confirmed that introducing Au nanopartiles with proper size would lead to the increase of photocurrent. The key challenges were to minimize the trap states and optimize the interface of nanostructures.

In order to collect the hot electrons, light trapping using cylindrical quartz substrates for ultra-thin a-Si:H photovoltaic cells with no doped layers is introduced. The photovoltaic cell has the structure of 2 nm MoOx (hole collection layer) – 10 nm intrinsic a-Si:H (photoactive layer) – 1.5 nm LiF / 300 nm Al (electron collection layer and back electrode), all deposited in that order onto a cylindrical quartz substrate covered with a 100 nm ITO layer, which is acting as the transparent front electrode for the cell. By rotating the cell with respect to the incoming light, the angle of incidence of the incoming light for which the cell efficiency is at its highest value, is determined.

Enhancing the light absorption and improving the charge collection are considered as two major prerequisite for achieving highly efficient bulk heterojunction organic solar cells (BHJ OSCs). In the present study, we have explored Ga doped ZnO as an electron transport layer for improving the charge collection in one of the promising donor: acceptor system comprised of Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b’]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th):phenyl-C71-butyric acid methyl ester (PC70BM). With the inverted geometry having a configuration of ITO/GZO (40nm)/PTB7-Th: PC70BM (100nm)/MoO3 (10nm)/Ag (100nm), maximum power conversion efficiency (PCE) of 7.24% has been achieved, while it is limited at 6.89% for devices with undoped ZnO.It was found that PCE can be further improved to 8.35 % after V-grooved textured PDMS films were attached to the backside of OSC substrates. We attribute this performance enhancement in OSCs is due to increased total optical path length of the incident light within the device.

We show that superlattice (SL) of PbS quantum dots (QD) can be easily prepared by drop casting of colloidal QD solution onto glass substrate and the ordering level can be controlled by the substrate temperature. A QD solution was dropped on glass and dried at 25, 40, 70 and 100°C resulting in formation of different SL structures. X-ray diffractograms (XRD) of deposited films show a set of sharp and intense peaks that are higher order satellites of a unique peak at 1.8 degrees (two theta), which corresponds, using the Bragg’s Law, to an interplanar spacing of 5.3 nm. The mean particles diameter, calculated through the broadening of the (111) peak of PbS using the Scherrer’s formula, were in agreement with the interplanar spacing. Transmission electron microscopy (TEM) measurements were also used to study the SL structure, which showed mainly a face centered cubic (FCC) arrangement of the QD. The photoluminescence (PL) spectrum of QD in the SL showed a shift toward lower energy compared to one in solution. It can be attributed to the fluorescence resonant energy transfer (FRET) between neighbors QD´s. Moreover, we observed greater redshift of PL peak for film with lower drying temperature, suggesting that it has a more organized structure.

Graphene is a 2-D carbon material showing considerable prominence in a wide range of optoelectronics, energy storage, thermal and mechanical applications. However, due to its unique features which are typically associated with difficulty in handling (ultra-thin thickness and hydrophobic surface, to name a few), synthesis and subsequent deposition processes are thus critical to the material properties of the prepared graphene films. While existing synthesis approaches such as chemical vapor deposition and epitaxial growth can grow graphene with high degree of order, the costly high temperature and/or high vacuum process prohibit the widespread usage, and the subsequent graphene transfer from the growth substrates for deposition proves to be challenging. Herein, a low-cost one-step synthesis and deposition approach for preparing few-layer graphene (FLG) on flexible copper substrates based on dry ball-free milling of graphite powder is proposed. Different from previous reports, copper substrates are inserted into the milling crucible, thus accomplishing simultaneous synthesis and deposition of FLG and eliminating further deposition step. Furthermore, while all previously reported high energy milling processes involve using balls of various sizes, we adopt a ball-free milling process relying only on centrifugal forces, which significantly reduces the surface damage of the deposition substrates. Sample characterization indicates that the process yields FLG deposited uniformly across all tested specimens. Consequently, this work takes graphene synthesis and deposition a step closer to full automation with simple and low-cost process.

In this work, the integration of ZnO-CuO core-shell nanostructures shows improvement in the conversion efficiency of ZnO-based dye-sensitized solar cells (DSSCs). This is due to CuO acting as a secondary absorption layer that allows the absorption of near-infrared (NIR) light increasing the generated photocurrent in the device, and as a blocking layer that reduces electron-hole recombination. The ZnO core and encapsulating CuO shell are synthesized through chemical vapor deposition (CVD), and thermal oxidation of a Cu seed layer, respectively. The crystallinity of the synthesized ZnO and CuO is analyzed by X-ray diffraction (XRD). Scanning electron microscope (SEM) images show the change in morphology through the steps of Cu seed layer deposition and thermal oxidation of this layer. To determine optical properties of CuO on ZnO nanorods, UV-Vis-NIR photospectrocopy is used. The comparison of conversion efficiency of DSSCs using two different photoelectrodes (i.e. ZnO nanorods versus ZnO-CuO core-shell nanostructure) is performed by I-V measurements.

An ultra-thin LiF layer in conjunction with an Al layer is employed as the electron collector for the a-Si:H based single-junction thin film photovoltaic cell. The cell has the structure of boron doped μ-SiOx (hole collector) - intrinsic a-Si:H (photoactive layer) - LiF / Al (electron collector and back electrode). The substrate used is U type Asahi glass, which is also acting as the transparent front electrode. For the cell with the 1.5 nm thick LiF layer, annealed at 120°C, the open current voltage (VOC) of 0.936 V, the short current density (JSC) of 13.598 mA/cm2, and the fill factor (FF) of 0.690 are achieved. The JSC and VOC values are comparable to the values measured for the a-Si:H based p-i-n reference cell, but the FF value is found to be lower, which is attributed to the losses due to recombination at the intrinsic a-Si:H / LiF / Al junction. The current versus voltage measurements are carried out under the standard test conditions. The JSC values are corrected according to the external quantum efficiency measurements of the cells in the AM1.5 spectrum region between 270 nm and 800 nm.

This work describes the electrical behavior of dye sensitized solar cells manufactured with TiO2-nanocrystalline semiconductor sensitized with diverse natural tints. A number of natural sensitizers have been tested, including red fruits as blackberries, hibiscus and beet in order to comprehend the relationship between anthocyanin and electron transfer and green vegetables as spinach and grass, as well as for known the relationship between chlorophyll and electron transfer. The nanocrystalline semiconductor was characterized by XRD, FTIR and SEM. The bands observed at 931, 667 and 514 cmˉ1 in the FTIR spectrum confirmed the presence of Ti-O-Ti bonds. From DRX analysis it is confirmed the presence of TiO2 in its anatase form. This study confirms the great potential of the use of organic dyes for sensitized the TiO2-semiconductor. Principally, in blackberries it has reached values around 300 mV owing to high concentrations of purple pigment due to the molecule called anthocyanin and the anchoring properties of the anthocyanin with the TiO2-nanocrystalline semiconductor.