High-performance solution-processable ZnO thin films for use as electron-transporting layers (ETLs) of inverted-structured polymer solar cells (I-PSCs) are developed via a low-temperature annealing (<200 C) sol-gel process. The properties of the low-temperature-annealed ZnO (L-ZnO) thin films (used as ETLs) are optimized based on the evaluation of the roles of the internal nanocrystal (NC) orientation and filmsurface morphology in charge transport/transfer in I-PSCs. The low-temperature annealing conditions (dynamic annealing or static annealing) could be successfully manipulated to alter the NC orientation of the L-ZnO films, whereas tactical control of the precursor-coating conditions enabled the embedding of nanoripples on the film surfaces. Suppression of the preferential (002) plane NC orientation of the L-ZnO layers is beneficial for charge transport in I-PSCs; these devices should be evaluated in a manner different from field-effect transistors (FETs). The performance of ETLs is further enhanced by the development of nanoripple-embedded L-ZnO film surfaces, which furnish an increased area for contact with the active layers. The I-PSCs fabricated using the optimized L-ZnO films display a >20% higher power-conversion efficiency (PCE) than those employing the conventional L-ZnO films for a range of active materials including poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PC 60 BM) and poly(thienothiophene-co-benzodithiophenes)7-F20 (PTB7-F20)/phenyl-C71-butyric acid methyl ester (PC 71 BM) blends. A PCE of 6.42% is achieved for the I-PSCs using the optimized L-ZnO films and PTB7-F20/PC 71 BM blends as the ETL and active materials, respectively. This study presents a universal method for optimizing sol-gel-driven ZnO-based ETLs, whilst the low-temperature processability and long-term stability of the developed ETLs are beneficial for the commercialization of I-PSCs.

In surface science, much effort has gone into obtaining a deeper understanding of the size-selectivity of nanocatalysts. In this article, electronic and chemical properties of various model catalysts consisting of Au are reported. Au supported by oxide surfaces becomes inert towards chemisorption and oxidation as the particle size became smaller than a critical size (2-3 nm). The inertness of these small Au nanoparticles is due to the electron-deficient nature of smaller Au nanoparticles, which is a result of metal-substrate charge transfer. Properties of Au clusters smaller than ∼20 atoms were shown to be non-scalable, i.e., every atom can drastically change the chemical properties of the clusters. Moreover, clusters with the same size can show dissimilar properties on various substrates. These recent endeavours show that the activity of a catalyst can be tuned by varying the substrate or by varying the cluster size on an atom-by-atom basis.

Toxic doping gases are usually used to produce hydrogenated amorphous silicon (a-Si:H) layers in thin-film solar cells (TFSCs). Hence, an alternative structure that avoids the use of toxic gases is desirable. In this work, we replaced both the p-type-a-Si:H and n-type-a-Si:H layers simultaneously in a normal TFSC to form a structure that is dopant-free. Molybdenum oxide (MoO3) and lithium fluoride were used as the p-type and n-type layers, respectively. The effects of the deposition method and the thickness of the MoO3 layer on the device performance were investigated. The power-conversion efficiency of the optimized hybrid solar cell reached a maximum of 7.08%, which is remarkable considering the novel structure of the dopant-free devices. The light stability of the devices with and without MoO3 was also compared: the light stability of the device with MoO3 was found to be much better than that of the device without MoO3 and with p-i-n Si layers. This was ascribed to the insignificant number of defect sites generated by the nondoping elements, which led to a less contaminated, more compact, and smoother oxide surface, resulting in an increase in the electron lifetime and improved light stability. This work opens up a new direction toward the development of a truly dopant-free device that does not involve the use of toxic gases during fabrication and provides the potential for further enhancement of the efficiency of future dopant-free solar cells.

A facile electrodeposition technique was utilized to deposit single-walled carbon nanotubes (SWNTs) with cadmium telluride (CdTe) with well-controlled size, density, surface morphology, and composition. By controlling the applied charge, the morphology of these hybrid nanostructures was altered from CdTe nanoparticles on SWNTs to SWNT/CdTe core/shell nanostructures and the composition of the CdTe nanoparticles was altered from Te-rich (29 at% Cd) to Cd-rich (79 at% Cd) CdTe by adjusting the deposition potential. The electrical and optoelectrical properties of these hybrid nanostructures showed that photo-induced current can be tuned by tailoring the conductivity type (n-type or p-type), morphology, and size of the CdTe nanostructures, with a maximum photosensitivity (ΔI/I(0)) of about 30% for SWNT/Cd-rich CdTe (n-type) core/shell nanostructures. This work demonstrates a novel approach for synthesizing metal chalcogenide/SWNT hybrid nanostructures for various electrical and optoelectrical applications.

Both polar and non-polar Cu2O thin films were electrodeposited in electrolytes of different pH, and their photoelectrochemical activities in water were analyzed. The surface morphology of these tailored-polarity Cu2O films was analyzed by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD), and their photoactivity was characterized through photoluminescence and Mott–Schottky measurement of the defect structure, diffusion length, carrier concentration, and charge separation. Through this, the tetrahedral surface morphology of a polar Cu2O thin film was found to exhibit a higher photocurrent in the visible spectrum than the pyramidal surface morphology of a non-polar Cu2O film. Furthermore, the higher flat-band potential and carrier concentration identified in the polar Cu2O by Mott–Schottky analysis was found to result in a higher charge separation.