Solvents induced ZnO nanoparticles aggregation associated with their interfacial effect on organic solar cells

Role of the ZnO electron transport layer in PbS colloidal quantum dot solar cell yield

The development of lead sulfide (PbS) colloidal quantum dot (CQD) solar cells has led to significant power conversion efficiency (PCE) improvements in recent years, with record efficiencies now over 15%. Many of the recent advances in improving PCE have focused on improving the interface between the PbS CQD active layer and the zinc oxide (ZnO) electron transport layer (ETL). Proper optimization of the ZnO ETL also increases yield, or the percentage of functioning devices per fabrication run. Simultaneous improvements in both PCE and yield will be critical as the field approaches commercialization. This review highlights recent advances in the synthesis of ZnO ETLs and discusses the impact and critical role of ZnO synthesis conditions on the PCE and yield of PbS CQD solar cells.

Nanocrystals as performance-boosting materials for solar cells

Nanocrystals (NCs) have been widely studied owing to their distinctive properties and promising application in new-generation photoelectric devices. In photovoltaic devices, semiconductor NCs can act as efficient light harvesters for high-performance solar cells. Besides light absorption, NCs have shown great significance as functional layers for charge (hole and electron) transport and interface modification to improve the power conversion efficiency and stability of solar cells. NC-based functional layers can boost hole/electron transport ability, adjust energy level alignment between a light absorbing layer and charge transport layer, broaden the absorption range of an active layer, enhance intrinsic stability, and reduce fabrication cost. In this review, recent advances in NCs as a hole transport layer, electron transport layer, and interfacial layer are discussed. Additionally, NC additives to improve the performance of solar cells are demonstrated. Finally, a summary and future prospects of NC-based functional materials in solar cells are presented, addressing their limitations and suggesting potential solutions.

Simultaneous Improvement of Efficiency and Stability of Organic Photovoltaic Cells by using a Cross-Linkable Fullerene Derivative

Improving power conversion efficiencies (PCEs) and stability are two main tasks for organic photovoltaic (OPV) cells. In the past few years, although the PCE of the OPV cells has been considerably improved, the research on device stability is limited. Herein, a cross-linkable material, cross-linked [6,6]-phenyl-C61-butyric styryl dendron ester (c-PCBSD), is applied as an interfacial modification layer on the surface of zinc oxide and as the third component into the PBDB-TF:Y6-based OPV cells to enhance photovoltaic performance and long-term stability. The PCE of the OPV cells that underwent the two-step modification increased from 15.1 to 16.1%. In particular, such OPV cells exhibited much better stability under both thermal and air conditions because of the decreased number of interfacial defects and stable interfacial and active layer morphologies. The results demonstrated that the introduction of a cross-linkable fullerene derivative into the interfacial and active layers is a feasible method to improve the PCE and stability of OPV cells.

Imaging of Neurotransmitters and Small Molecules in Brain Tissues Using Laser Desorption/Ionization Mass Spectrometry Assisted with Zinc Oxide Nanoparticles

Inorganic nanostructured materials such as silicon, carbon, metals, and metal oxides have been explored as matrices of low-background signals to assist the laser desorption/ionization (LDI) mass spectrometric (MS) analysis of small molecules, but their applications for imaging of small molecules in biological tissues remain limited in the literature. Titanium dioxide is one of the known nanoparticles (NP) that can effectively assist LDI MS imaging of low molecular weight molecules (LMWM). TiO₂ NP is commercially available as dispersions, which can be applied using a chemical solution sprayer. However, aggregation of NP can occur in the dispersions, and the aggregated NP can slowly clog the sprayer nozzle. In this work, the use of zinc oxide (ZnO) NP for LDI MS imaging is investigated as a superior alternative due to its dissolution in acidic pH. ZnO NP was found to deliver similar or better results in the imaging of LMWM in comparison to TiO₂ NP. The regular acid washes were effective in minimizing clogging and maintaining high reproducibility. High-quality images of mouse sagittal and rat coronal tissue sections were obtained. Ions were detected predominately as Na⁺ or K⁺ adducts in the positive ion mode. The number of LMWM detected with ZnO NP was similar to that obtained with TiO₂ NP, and only a small degree of specificity was observed.

High colloidal stability ZnO nanoparticles independent on solvent polarity and their application in polymer solar cells

Significant aggregation between ZnO nanoparticles (ZnO NPs) dispersed in polar and nonpolar solvents hinders the formation of high quality thin film for the device application and impedes their excellent electron transporting ability. Herein a bifunctional coordination complex, titanium diisopropoxide bis(acetylacetonate) (Ti(acac)2) is employed as efficient stabilizer to improve colloidal stability of ZnO NPs. Acetylacetonate functionalized ZnO exhibited long-term stability and maintained its superior optical and electrical properties for months aging under ambient atmospheric condition. The functionalized ZnO NPs were then incorporated into polymer solar cells with conventional structure as n-type buffer layer. The devices exhibited nearly identical power conversion efficiency regardless of the use of fresh and old (2 months aged) NPs. Our approach provides a simple and efficient route to boost colloidal stability of ZnO NPs in both polar and nonpolar solvents, which could enable structure-independent intense studies for efficient organic and hybrid optoelectronic devices.

Ultrafine Rh nanoparticles confined by nitrogen-rich covalent organic frameworks for methanolysis of ammonia borane

An Rh/PC-COF was synthesized using a metal–nitrogen coordination reduction strategy and was applied as a highly efficient catalyst for methanolysis of ammonia borane.

Silane-Capped ZnO Nanoparticles for Use as the Electron Transport Layer in Inverted Organic Solar Cells

Zinc oxide (ZnO) nanoparticles are widely used as electron- transport layer (ETL) materials in organic solar cells and are considered to be the candidate with the most potential for ETLs in roll-to-roll (R2R)-printed photovoltaics. However, the tendency of the nanoparticles to aggregate reduces the stability of the metal oxide inks and creates many surface defects, which is a major barrier to its printing application. With the aim of improving the stability of metal oxide nanoparticle dispersions and suppressing the formation of surface defects, we prepared 3-aminopropyltrimethoxysilane (APTMS)-capped ZnO (ZnO@APTMS) nanoparticles through surface ligand exchange. The ZnO@APTMS nanoparticles exhibited excellent dispersibility in ethanol, an environmentally friendly solvent, and remained stable in air for at least one year without any aggregation. The capping of the ZnO nanoparticles with APTMS also reduced the number of surface-adsorbed oxygen defects, improved the charge transfer efficiency, and suppressed the light-soaking effect. The thickness of the ZnO@APTMS ETL could reach 100 nm without an obvious decrease in the performance. Large-area APTMS-modified ZnO films were successfully fabricated through roll-to-roll microgravure printing and exhibited good performance in flexible organic solar cells. This work demonstrated the distinct advantages of this ZnO@APTMS ETL as a potential buffer layer for printed organic electronics.

Development of Annealing-Free, Solution-Processable Inverted Organic Solar Cells with N-Doped Graphene Electrodes using Zinc Oxide Nanoparticles

An annealing-free process is considered as a technological advancement for the development of flexible (or wearable) organic electronic devices, which can prevent the distortion of substrates and damage to the active components of the device and simplify the overall fabrication process to increase the industrial applications. Owing to its outstanding electrical, optical, and mechanical properties, graphene is seen as a promising material that could act as a transparent conductive electrode for flexible optoelectronic devices. Owing to their high transparency and electron mobility, zinc oxide nanoparticles (ZnO-NP) are attractive and promising for their application as charge transporting materials for low-temperature processes in organic solar cells (OSCs), particularly because most charge transporting materials require annealing treatments at elevated temperatures. In this study, graphene/annealing-free ZnO-NP hybrid materials were developed for inverted OSC by successfully integrating ZnO-NP on the hydrophobic surface of graphene, thus aiming to enhance the applicability of graphene as a transparent electrode in flexible OSC systems. Chemical, optical, electrical, and morphological analyses of ZnO-NPs showed that the annealing-free process generates similar results to those provided by the conventional annealing process. The approach was effectively applied to graphene-based inverted OSCs with notable power conversion efficiencies of 8.16% and 7.41% on the solid and flexible substrates, respectively, which promises the great feasibility of graphene for emerging optoelectronic device applications.

Interface passivation and electron transport improvement of polymer solar cells through embedding a polyfluorene layer

The TiO₂ cathode interface layer modified by a polyfluorene interlayer results in a considerable effect on polymer solar cells.

Enhanced electron extraction capability of polymer solar cells via modifying the cathode buffer layer with inorganic quantum dots

Inorganic quantum dots were employed to modify the electron transporting layer of PSCs, and a great enhancement of PCE was achieved.

In Situ Formation of ZnO in Graphene: A Facile Way To Produce a Smooth and Highly Conductive Electron Transport Layer for Polymer Solar Cells

A novel electron transport layer (ETL) based on zinc oxide@graphene:ethyl cellulose (ZnO@G:EC) nanocomposite is prepared by in situ formation of zinc oxide (ZnO) nanocrystals in a graphene matrix to improve the performance of polymer solar cells. Liquid ultrasound exfoliation by ethyl cellulose as stabilizer not only allows for uniform dispersion of graphene solution but also maintains an original structure of graphene gaining a high conductivity. The ZnO@G:EC ETL displays a quite smooth morphology and develops the energy-level alignment for the electron extraction and transportation. Subsequently, the device based on poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C61 butyric acid methyl ester (PC61BM) with the ZnO@G:EC as ETL obtains a power conversion efficiency (PCE) of 3.9%, exhibiting a ∼20% improvement compared to the familiar device with bare ZnO nanocrystals as ETL. Replacing the active layer with polythieno[3,4-b]thiophene/benzodithiophene (PTB7): (6,6)-phenyl-C71 butyric acid methyl ester (PC71BM), the PCE can be dramatically improved to 8.4%. This facile and fascinating method to produce a smooth and highly conductive electron transport layer provides an anticipated approach to obtain high performance polymer solar cells.