Increase In Photoconversion Efficiency Research Articles

Highly efficient visible-light-driven CdS-loaded ZnO-GaN nanowire photoanode fabricated on Si for H2 evolution

GaN nanowires (NWs) are considered promising photoelectrode materials owing to their direct bandgap, which a high-efficiency photon absorption. Additionally, their conduction and valence bands straddle the water redox level, making them ideal candidates for solar water splitting without external biasing. Moreover, they have a large reactive surface area, which promotes charge separation. However, their practical applicability is limited because of their poor stability and low solar-to-hydrogen conversion efficiency, which can be mitigated by loading a passivation layer and cocatalyst onto the GaN NW surfaces. In this study, CdS/ZnO/GaN NW photoanodes were fabricated on Si substrates for photoelectrochemical water splitting. Vapor–liquid–solid GaN NWs were used as the core material on a Si substrate passivated with a ZnO conformal layer, and CdS was adopted as a cocatalyst. Compared to a ZnO/GaN NW photoanode, the CdS/ZnO/GaN NW photoanode showed a 10-fold increase in photocurrent density and a 47-fold increase in photoconversion efficiency under 1-Sun illumination. We propose that ZnO and CdS inhibit the photocorrosion of bare GaN NWs and thus reduce the surface defects, thereby lowering the photogenerated charge recombination rate. As a result, the stability of GaN NWs in a high pH electrolyte increases, leading to an efficient H2 evolution.

A Review of the Impact of Zinc Oxide Nanostructure Morphology on Perovskite Solar Cell Performance

Zinc oxide (ZnO) has been widely studied over the last decade for its remarkable properties in optoelectronic and photovoltaic devices because of its high electron mobility and excitonic properties. It has probably the broadest range of nanostructured forms that are also easy and cheap to synthesize using a wide variety of methods. The volume of recent work on ZnO nanostructures and their devices can potentially overshadow significant developments in the field. Therefore, there is a need for a concise description of the most recent advances in the field. In this review, we focus on the effect of ZnO nanostructure morphologies on the performance of ZnO-based solar cells sensitized using methylammonium lead iodide perovskite. We present an exhaustive discussion of the synthesis routes for different morphologies of the ZnO nanostructure, ways of controlling the morphology, and the impact of morphology on the photoconversion efficiency of a given perovskite solar cell (PSC). We find that although the ZnO nanostructures are empirically similar, one-dimensional structures appear to offer the most promise to increasing photoconversion efficiency (PCE) by their proclivity to align and form vertically stacked layers. This is thought to favor electron hopping, charge mobility, and conductivity by allowing multiple charge conduction pathways and increasing the effective junction cross-sectional area. The combined effect is a net increase in PCE due to the reduced surface reflection, and improved light absorption.

Effect of wettability of substrate on metal halide perovskite growth

In the last decade, inorganic–organic hybrid perovskites have demonstrated a dramatic increase in photoconversion efficiency by engineering the perovskite composition, as well as adjusting the properties of the charge transporting materials. The nucleation and growth of the perovskite layer are governed by the surface properties of the substrate and depend on its wetting properties defined by the roughness and the species adsorbed. Fixing all fabrication conditions of a PSC but only changing the wettability of the substrate is practically difficult because varying the surface hydrophilicity can contribute side effects such as chemical identity change or adsorption of new species on the surface. Herein, we studied a double-layered TiO2/SnO2 ETL for perovskite deposition and we changed the hydrophilicity of the samples using hydrophobic recovery after UV exposure. Thus, the effect of wettability of the substrate on nucleation and growth of the perovskite layer was elucidated under minimized interference. It was found that the influence of the wetting properties of the substrate on the growth of perovskite can be exaggerated in the literature since the increase in the grain size of the perovskite layer is just 14% bigger if the water contact angle of the substrate increases from 3° to 72°.

High efficient hybrid bulk hetero junction thin-film solar cell embedded with kesterite Cu2ZnSnS4 quantum dots

The photovoltaic performance of kesterite Cu 2 ZnSnS 4 (CZTS) quantum dot (QD) incorporated poly(3-hexylthiophene-2,5-diyl) (Alvarado et al., 1998; Alvarado et al., 1998) [6,6]: phenyl-C61butyric acid hexyl ester (P3HT:PCBH) polymer matrix based organic hybrid heterojunction solar cell configuration is investigated. The inorganic filler material CZTS QDs with P3HT:PCBH matrix, forms double bulk hetero junction (BHJ) throughout in the active layer, which facilitates rapid exciton dissocitaion process at P3HT:PCBH and CZTS:PCBH interfaces that results effective charge carrier separation. The prepared active layer material has been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), Raman and fourier transform infra red (FTIR). The enhanced optical absorbance of prepared hybrid structure has been verified by UV–Visible analysis. It has been observed that the improvement in photo conversion efficiency (PCE) from 2.36% for the solar cell device P3HT:PCBH to 4.12% for CZTS QD based P3HT:PCBH hybrid organic solar cell device. This dramtaic increase in PCE, is mainly due to the significant enhancement in short-circuit current density (J sc ) from 7.6 mA/cm 2 to 11.2 mA/cm 2 . That suggests, the incorporation of p-type kesterite CZTS QDs into P3HT:PCBH polymer matrix enhances the effective exciton dissociation at interfaces resulting charge separation and their fast extraction to electrodes inhibiting e − /h + pair recombination. Furthermore, the hybrid solar cell shows remarkable time stability retaining 80% of original PCE measured after 30 days under ambient environment conditions. The hybrid organic solar cell device shows thermal stability by retaining 95.6% of its intial efficiency measured which has been tested in the temperature range 20–80 °C. • Photovoltaic performance of CZTS QDs:P3HT:PCBH hybrid thin film solar cell is investigated. • PCE of hybrid device has been observed to enhance from 2.36% to 4.12%. • It shows time and thermal stability retaining 80% and 95.6% efficiency.

Enhancing the Photovoltaic Performance of Dye-Sensitized Solar Cells with Rare-Earth Metal Oxide Nanoparticles

Doping titania with rare-earth metals improves the photoconversion efficiency (PCE) of dye sensitized solar cells (DSSCs). In most reported cases, the overall cell quality is not optimal, making it unclear what role the rare earth oxide metal plays in the improvement, if any. Here we incorporate <100 nm diameter nanoparticles of neodymium and erbium oxide into titania films and test their performance in high quality DSSCs. The doping level for optimized cells is 2.0% and 1.0% for neodymium oxide and erbium oxide by weight, respectively. This results in a 5 to 10% increase in PCE for the rare earth oxide doped DSSCs relative to undoped DSSCs, with erbium oxide being the best. The rare-earth metal-doped films exhibit a 20–25% larger dye loading and the loading was maximum at the same doping levels where the PCE was maximum, showing this is a big contributor to the improvement. The surface area is larger with rare-earth doped titania as determined by atomic force microscopy and BET analysis, explaining the higher dye loading. The cell impedance is lower with rare-earth doped samples, showing that the rare-earth metal oxide also facilitates electron transport through the mesoporous titania, improving the collection efficiency of the photoexcited electrons.

Band edge movement and structural modifications in transition metal doped TiO2 nanocrystals for the application of DSSC

Nanocrystalline undoped and transition metal ion doped (TM:Cu2+, Mn2+ and Fe3+) TiO2 nanoparticles, with 1 mol% were synthesized by a simple and cost effective modified co-precipitation method at room temperature and were successfully used as photoanode for dye sensitized solar cell (DSSC). The effect of transition metal ions into TiO2 nano crystalline powder has been systematically investigated using x-ray diffraction (XRD), UV–Vis spectroscope, scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive x-ray spectroscopy (EDX). The results of XRD confirm nanocrystalline anatase tetragonal structure of prepared undoped and TM doped TiO2 semiconductor. The influence of doping on band edge movement has been estimated using UV–visible spectroscopy. The SEM results indicate that microscopic effect of doping on morphology of the TiO2. The peaks of EDX signify incorporation of transition metal cations into TiO2 lattice. The effect of doping on flat band potential was estimated using interpolation on Mott-Schottky plot. The performances of DSSCs of undoped and doped TiO2 photoelectrodes were investigated under light illumination. In comparison with undoped and (Cu2+, Fe3+) doped TiO2 photoanodes we found that incorporation of Mn2+ into TiO2 exhibits improvement in photoconversion efficiency (η). There is increase in photoconversion efficiency of DSSCs with Mn2+ doped TiO2 by 6% as compared to that of undoped TiO2 photoanode.

Tuning flat band potential of TiO2 using an electrolyte additive to enhance open circuit voltage and minimize current loss in dye sensitized solar cells

Electrolyte is an important component of dye sensitised solar cells (DSSC). Its composition, in particular, additives controls the energetic at the TiO2/dye/electrolyte interface, influencing the performance of dye solar cell. We report here for the first time the use of 8-Hydroxyquinoline (8HQ) as an electrolyte additive to replace costly, volatile 4-tert-butyl pyridine (TBP). Due to its unique structural feature containing hydroxyl and amine group, 8HQ results in remarkable difference in the energy band alignment at the TiO2/dye/electrolyte interface with respect to that of TBP, as revealed by photocurrent density and Mott-Schottky analysis. Apart from this band shift, 8HQ is very effective in suppressing back electron transfer resulting in enhancement in open circuit voltage. Compared to TBP, additive 8HQ resulted in ∼22% increase in Jsc, with minor loss in Voc (∼5.8%) and 15% increase in photoconversion efficiency with N3 dye. Overall, we found that 8HQ is a highly effective additive in tailoring the TiO2/dye/electrolyte interface which results in superior performance of dye sensitized solar solar cells as compared to cells with TBP as the additive.

Three-dimensional scanning near field optical microscopy (3D-SNOM) imaging of random arrays of copper nanoparticles: implications for plasmonic solar cell enhancement.

In order to investigate the suitability of random arrays of nanoparticles for plasmonic enhancement in the visible-near infrared range, we introduced three-dimensional scanning near-field optical microscopy (3D-SNOM) imaging as a useful technique to probe the intensity of near-field radiation scattered by random systems of nanoparticles at heights up to several hundred nm from their surface. We demonstrated our technique using random arrays of copper nanoparticles (Cu-NPs) at different particle diameter and concentration. Bright regions in the 3D-SNOM images, corresponding to constructive interference of forward-scattered plasmonic waves, were obtained at heights Δz ≥ 220 nm from the surface for random arrays of Cu-NPs of ∼ 60-100 nm in diameter. These heights are too large to use Cu-NPs in contact of the active layer for light harvesting in thin organic solar cells, which are typically no thicker than 200 nm. Using a 200 nm transparent spacer between the system of Cu-NPs and the solar cell active layer, we demonstrate that forward-scattered light can be conveyed in 200 nm thin film solar cells. This architecture increases the solar cell photoconversion efficiency by a factor of 3. Our 3D-SNOM technique is general enough to be suitable for a large number of other applications in nanoplasmonics.

Active Layer-Incorporated, Spectrally Tuned Au/SiO2 Core/Shell Nanorod-Based Light Trapping for Organic Photovoltaics

We demonstrate that incorporation of octadecyltrimethoxysilane (OTMS)-functionalized, spectrally tuned, gold/silica (Au/SiO2) core/shell nanospheres and nanorods into the active layer of an organic photovoltaic (OPV) device led to an increase in photoconversion efficiency (PCE). A silica shell layer was added onto Au core nanospheres and nanorods in order to provide an electrically insulating surface that does not interfere with carrier generation and transport inside the active layer. Functionalization of the Au/SiO2 core/shell nanoparticles with the OTMS organic ligand was then necessary to transfer the Au/SiO2 core/shell nanoparticles from an ethanol solution into an OPV polymer-compatible solvent, such as dichlorobenzene. The OTMS-functionalized Au/SiO2 core/shell nanorods and nanospheres were then incorporated into the active layers of two OPV polymer systems: a poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCB60M) OPV device and a poly[2,6-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,4-b]dithiophene-alt-5-dibutyloctyl-3,6-bis(5-bromothiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione] (PBDTT-DPP:PC60BM) OPV device. For the P3HT:PC60BM polymer with a band edge of ~700 nm, the addition of the core/shell nanorods with an aspect ratio (AR) of ~2.5 (extinction peak ~670 nm) resulted in a 7.1% improvement in PCE, while for the PBDTT-DPP:PC60BM polymer with a band edge of ~860 nm, the addition of core/shell nanorods with an AR of ~4 (extinction peak ~830 nm) resulted in a 14.4% improvement in PCE. The addition of Au/SiO2 core/shell nanospheres to the P3HT:PC60BM polymer resulted in a 2.7% improvement in PCE, while their addition to a PBDTT-DPP:PC60BM polymer resulted in a 9.1% improvement. The PCE and Jsc enhancements were consistent with external quantum efficiency (EQE) measurements, and the EQE enhancements spectrally matched the extinction spectra of Au/SiO2 nanospheres and nanorods in both OPV polymer systems.