Dr. Theresa Kueckmann, Editor-in-Chief of Chemistry – An Asian Journal, talks to Professor Qichun Zhang, Nanyang Technological University, Singapore, about his article on electron-transport layer materials for perovskite solar cells, which was recently published.
Professor Zhang, you developed an azaacene derivative for electron transport in solar cells. What inspired you to pursue this topic?
Our group has been working on azaacene materials for more than six years and we know that these materials are excellent air-stable semiconductors with good electron mobility. We strongly believe that this type of material should find application as active layers in organic field-effect transistors or as electron-transport layers for semiconductor devices.
Recently, perovskite-based photovoltaics have started to be considered as possible next-generation solar cells for practical applications. The traditional-architecture perovskite photovoltaics (n-i-p type) have a sandwich-like structure with metal halide perovskites as active elements, metal oxides as the electron-transport layer, and organic materials as the hole-transport layer. While this type of solar cells shows good performance, high-temperature annealing is required for the preparation of metal oxides. This has become a bottleneck for the large-scale fabrication of solar cells for practical applications. To address this problem, inverted perovskite solar cells (PSCs, p-i-n type) without metal oxide layers are becoming the research focus due to their low-temperature and solution-based processing.
Despite the advantages of metal-oxide-free inverted perovskite solar cells, it is still very challenging to find suitable organic electron transport layer (ETL) candidates, which are easily synthesized at low cost and which can be easily solution-processed to achieve high-performance devices. Based on our research experience, we believe that azaacenes could be promising ETL candidates to boost the efficiency of inverted perovskite solar cells.
New materials for solar cells are a popular research topic at the moment. Why was your attention focused on azaacenes?
Although some n-type molecules, e.g., phenyl-C61-butyric acid methyl ester, known as PCBM, have been reported as ELTs in inverted perovskite solar cells, further modification of these materials to reach stable high performance is very difficult. Azaacenes are small molecules whose energy levels are very easy to tune by simple functionalization to match the band position of the light absorption layer. In addition, this type of material is cheap and easy to scale up for practical application.
Do you have any plans for future work extending from this study?
Our future work will focus on designing new azaacenes. This could allow us to engineer the interface between the perovskite layer and the ELT and dramatically improve the interfacial interaction between these two layers to achieve high-performance solution-processed metal-oxide-free perovskite solar cells.
Why did you choose this approach?
Azaacenes can be processed in solution, in contrast to the metal oxides that are conventionally used for electron transport in perovskite solar cells. This solution processing makes device fabrication much easier and more energy-efficient.
Which part of your work proved the most challenging?
The most challenging part in my research is designing suitable, stable, and solution-processable azaacenes, which can provide us more chances for interface engineering between ETLs and perovskite layers.
Thank you for the interview.
- An Azaacene Derivative as Promising Electron-Transport Layer for Inverted Perovskite Solar Cells,
Pei-Yang Gu, Ning Wang, Anyang Wu, Zilong Wang, Miaomiao Tian, Zhisheng Fu, Xiao Wei Sun, Qichun Zhang,
Chem. Asian J. 2016.