Increasing The Efficiency Of Organic Solar Cells Through Improving ZnO Conductivity

A power conversion efficiency (PCE) of over 13% has been accomplished for single-junction polymer solar cell (PSCs) through the preparation of novel donating materials and interfacial engineering (surface modification). The interfacial layer is essential for improving charge extraction to the electrodes, avoiding non-ohmic contact losses, suppressing recombination, and exaction quenching of the charge carrier at the interfaces.

However, due to the relatively low charge mobility, most devices with high performance are made by very thin interlayers (2-10 nm). This is a significant restriction in large-scale processing methods for flexible substrates. Among the n-type solution-processed metal oxides based interfacial materials used in inverted PSCs, zinc oxide (ZnO) is a promising candidate due to its well-adapted energy level for electron extraction from the fullerene derivatives. In addition to its physical and chemical stability and tunable optical properties. However, due to its relatively low conductivity, pure ZnO is not appropriate to form a thick layer, which is not applicable to large-scale roll-to-roll processing. So it is necessary to improve the conductivity of ZnO by various methods to obtain a thickness-insensitive ZnO cathode buffer layer.


Recently, professor Yiwang Chen and his collaborator prof. Licheng Tan, together with his Ph.D. candidate Miss Yilin Wang from Nanchang University, China reported the highly stable Al-Doped ZnO by ligand-free synthesis as general thickness-insensitive interlayers for organic solar cells.


One of the available methods is to prepare metallic element-doped ZnO with high conductivity by doping the main group elements, such as aluminum (Al), gallium (Ga) and indium (In). This can adjust the energy level, optical and electrical properties of ZnO, subsequently improving the corresponding device performance. The doping of the main group-III elements can effectively passivate ZnO surface traps since the doped elements can replace Zn sites and serve as n-type dopants to generate free electrons. The most extensive Al-doped ZnO (AZO) is easy to achieve and possesses higher conductivity, which can be utilized as thickness-insensitive ETLs in large-scale roll-to-roll production.

In this work, highly conductive and surfactant-stable AZO NPs have been prepared by a colloidal synthesis procedure at low temperature. This involves stabilization by surfactant-aid including ethanolamine (EA), ethylenediamine (EDA), diethylenetriamine (DETA) and triethylenetetramine (TETA). Due to strong intermolecular hydrogen-bonding interactions between AZO NPs and the amino groups from surfactants, the inevitable aggregation was suppressed and the surface defect sites were passivated. The existence of electron transfer from the nitrogen of the amino groups to the zinc of AZO led to a dramatically increased electrical conductivity.


A homogeneous current intensity value up to ~2200 pA for AZO tread by DETA was characterized by conductive atomic force microscopy (C-AFM). This was more superior than that of the reported sol-gel synthesized AZO with the assistance of EA surfactant (refer to 170.7 pA). An optimal power conversion efficiency of 8.6% was achieved with 35 nm AZO-DETA as an electron transporting layer in the inverted polymer solar cells based on PTB7-Th:PC71BM. The device maintained 8.2% efficiency with a thick interlayer over 80 nm and excellent storage stability. Furthermore, non-fullerenes solar cells based on PBDB-T:ITIC with AZO-DETA (80 nm) yielded the best device efficiency of 10.7% and kept up prominent PCE exceeding 10% even with a thicker interlayer (95 nm).

The highly conductive and surfactant-stable AZO NPs by colloidal synthesis at low temperature may open new opportunities for roll-to-roll fabrication of thickness-insensitive ETLs for inverted PSCs.

These findings are described in the article entitled Highly stable Al-doped ZnO by ligand-free synthesis as general thickness-insensitive interlayers for organic solar cells, published in the journal Science China Chemistry. This work was led by Licheng Tan & Yiwang ChenĀ from Nanchang University.



Sequence-Defined Molecules Can Be Used To Create 2D Nanomaterials

The unique sequence-defined property endows materials scientists with the ability to precisely tailor and adjust the combination of functional groups […]

8 Micronesian Islands Just Sank Into The Pacific

Global climate change represents what may be the single biggest threat to modern society and our way of life. Climate […]

Real-time Detection Of Toxic Copper In Environment Monitoring And Public Health

Copper is an essential element in the environment and human body, but at the same time, exposure to high concentrations […]

Comparison Of Dietary Fibre Composition Of Old & Modern Durum Wheat Genotypes

As the dominant staple crop in temperate regions of the world, wheat provides between 20% to 50% of the total […]

How Vulnerable Is European Seafood Production To Climate Warming?

The world population increases at a rate of 1% every year. Today, we are 7 billion, and the world population […]

An Army Of Mutant Cloned Crayfish Is Taking Over Europe

A species of crayfish is able to clone itself, producing biologically fertile offspring just from the eggs of the mother […]

Cancer Vaccine Found To Cure 97% Of Tumors In Mice: To Begin Human Testing

Cancer is a very large and costly, in terms of lives and money, problem that the world faces. Recently, a […]

Science Trends is a popular source of science news and education around the world. We cover everything from solar power cell technology to climate change to cancer research. We help hundreds of thousands of people every month learn about the world we live in and the latest scientific breakthroughs. Want to know more?