Low-Cost, Air-Processed Quantum Dot Solar Cells via Diffusion-Controlled Synthesis.

Despite significant advances in the development of high-efficiency and stable quantum dot (QD) solar cells (QDSCs), recent synthetic and fabrication routes still require improvements to render QDSCs commercially feasible. Here, we describe a low-cost, industrially viable fabrication method of QDSCs under an ambient atmosphere (humid air and room temperature) using stable, high-quality, and small-sized PbS QDs prepared with low-cost, greener precursors [i.e., thioacetamide (TAA)] compared to the widely used bis(trimethylsilyl)sulfide [(TMS)2S], at low temperatures without requiring any stringent conditions. The low reaction temperature, medium reactivity of TAA, and diffusion-controlled particle growth adopted in this approach provide an opportunity to synthesize ultrasmall (emission peak ∼700 nm) to larger PbS QDs (emission peak ∼1050 nm). This also enables well-controlled large-scale (multigram) synthesis with a rough estimated production cost of PbS of 8.11 $ per gram (based on materials cost), which is the lowest among the available PbS QDs produced using wet chemistry routes. QDSCs fabricated using 3.25 nm PbS QDs (bandgap 1.29 eV) under ambient conditions yield a high circuit current density (Jsc) of 32.4 mA/cm2 (one of the highest values of Jsc ever reported) with a power conversion efficiency of 7.8% under 1 sun simulated sunlight at AM 1.5 G (100 mW/cm2). These devices exhibit better photovoltaic performance compared to devices fabricated with more traditional PbS QDs synthesized with (TMS)2S under an ambient atmosphere, confirming the quality of PbS QDs produced with our method. The diffusion-controlled TAA-based synthetic route developed herein is found to be very promising for synthesizing size-tunable PbS QDs for photovoltaic and other optoelectronic applications.

Synergistic Effect of Plasmonic Gold Nanoparticles Decorated Carbon Nanotubes in Quantum Dots/TiO2 for Optoelectronic Devices.

Here, a facile approach to enhance the performance of solar-driven photoelectrochemical (PEC) water splitting is described by means of the synergistic effects of a hybrid network of plasmonic Au nanoparticles (NPs) decorated on multiwalled carbon nanotubes (CNTs). The device based on TiO2-Au:CNTs hybrid network sensitized with colloidal CdSe/(CdSe x S1- x )5/(CdS)1 core/alloyed shell quantum dots (QDs) yields a saturated photocurrent density of 16.10 ± 0.10 mA cm-2 [at 1.0 V vs reversible hydrogen electrode (RHE)] under 1 sun illumination (AM 1.5G, 100 mW cm-2), which is ≈26% higher than the control device. The in-depth mechanism behind this significant improvement is revealed through a combined experimental and theoretical analysis for QDs/TiO2-Au:CNTs hybrid network and demonstrates the multifaceted impact of plasmonic Au NPs and CNTs: i) hot-electron injection from Au NPs into CNTs and TiO2; ii) near-field enhancement of the QDs absorption and carrier generation/separation processes by the plasmonic Au NPs; iii) enhanced photoinjected electron transport due to the highly directional pathways offered by CNTs. These results provide fundamental insights on the properties of QDs/TiO2-Au:CNTs hybrid network, and highlights the possibility to improve the performance of other solar technologies.

A colloidal heterostructured quantum dot sensitized carbon nanotube-TiO2 hybrid photoanode for high efficiency hydrogen generation.

Solar-driven photoelectrochemical (PEC) hydrogen (H2) generation is a promising approach to harvest solar energy for the production of a clean chemical fuel. However, the low photon-to-fuel conversion efficiency and long-term stability of PEC devices are major challenges to be addressed to enable large-scale commercialization. Here we report a simple, fast and cost-effective approach to fabricate high efficiency and stable PEC devices for H2 generation, by fabricating a hybrid photoanode obtained by incorporating small amounts of multiwall carbon nanotubes (MWCNTs) into a TiO2 mesoporous film and sensitizing with colloidal heterostructured CdSe/(CdSexS1-x)5/(CdS)2 quantum dots (QDs). The latter were specially designed to accelerate the exciton separation through a band engineering approach. The PEC devices based on the TiO2/QD-MWCNT (T/Q-M) hybrid photoanode with an optimized amount of MWCNTs (0.015 wt%) yield a saturated photocurrent density of 15.90 mA cm-2 (at 1.0 VRHE) under one sun illumination (AM 1.5G, 100 mW cm-2), which is 40% higher than that of the reference device based on TiO2/QD (T/Q) photoanodes. This is attributed to a synergistic effect of the promising optoelectronic properties of the colloidal heterostructured QDs and improved electron transport (reduced charge transfer resistance) within the TiO2-MWCNT hybrid anodes enabled by the directional path of MWCNTs for the photo-injected electrons towards FTO. Furthermore, the PEC device based on the T/Q-M hybrid photoanode is more stable (∼19% loss of its initial photocurrent density) when compared with the T/Q photoanode (∼35% loss) after two hours of continuous one sun illumination. Our results provide fundamental insights and a different approach to improve the efficiency and long-term stability of PEC devices and represent an essential step towards the commercialization of this emerging solar-to-fuel conversion technology.

Towards Long-Term Thermal Stability of Dye-Sensitized Solar Cells Using Multiwalled Carbon Nanotubes.

In this study, the effect of incorporating multiwalled carbon nanotubes (MWCNTs) on the thermal stability of dye-sensitized solar cells (DSSCs) was investigated. Under identical measurement conditions (aging at 80 °C for 240 h), DSSCs based on a bare TiO2 anode presented a significant loss in photoconversion efficiency (PCE), dropping to 59 % of their initial value, whereas the DSSCs based on a TiO2 -MWCNT nanocomposite anode attained a promising thermal stability with only 20 % loss of PCE. This degradation of cell performance is mainly associated with a dramatic reduction in the short-circuit current density (Jsc ). To understand the mechanisms that underpin these changes in device performance under thermal stress, both types of cells were investigated using various techniques. The incorporation of MWCNTs could eliminate the formation of cracks and improve electron charge transfer. The results of this study indicate a promising new method to enhance the thermal stability of DSSCs using a nanocomposite anode made of one-dimensional carbon materials.