A new method could enable researchers to fabricate more efficient and longer lasting perovskite solar cells, LEDs and photodetectors.
By growing thin perovskite films on substrates with different compositions, engineers at the University of California San Diego have invented a way of fabricating perovskite single crystals with precisely deformed, or strained, structures.
The work was published Jan. 8 in Nature.
Engineering a small amount of strain in perovskites is of great interest because it provides a way to make significant changes in the material's properties, such as how it conducts electricity, absorbs and transmits light, or how stable it is.
"You can use strain engineering as a knob to tune existing functions or even install new functions in a material," said Sheng Xu, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering and the senior author of the study.
There are techniques that use heat to introduce strain in perovskite crystals, but that strain is typically short lived or uncontrollable in terms of its magnitude, which makes these strain-engineered perovskites impractical to use. Existing strain engineering techniques are also incompatible with device fabrication processes.
Xu and his team tackled these problems by carefully growing deformed perovskite single crystals. Their technique permanently embeds strain into the material's structure and allows them to tailor the amount of strain--the more deformed the crystal lattice, the higher the strain.
The type of perovskite investigated in this study is alpha-formamidinium lead iodide, which has been used to create the highest efficiency perovskite solar cells to date. The researchers grew crystals of the material on a series of perovskite substrates with varying compositions and lattice sizes--a process called heteroepitaxial growth.
As the material crystallized, it adopted the lattice size of its substrate, which essentially forced the alpha-formamidinium lead iodide crystals to grow differently than they normally do.
"Thus, the lattices in the material are deformed and strained to different degrees, depending on the lattice mismatch between material and substrate," explained Yimu Chen, a nanoengineering Ph.D. student in Xu's lab and co-first author of the study.
"Because we are introducing strain at the atomic level, we can precisely design the strain and control it," said Yusheng Lei, who is also a nanoengineering Ph.D. student in Xu's lab and the other co-first author of the study.
The researchers grew perovskite crystals with five different levels of strain ranging from 0 to -2.4%. They found that -1.2% strain produced samples with the best charge-carrier mobility.
The team also reported another interesting discovery: growing alpha-formamidinium lead iodide crystals with strain stabilized its photoactive alpha phase.
"In its strain-free form, alpha-formamidinium lead iodide undergoes a phase transition from a photoactive phase to a non-photoactive phase, which is bad for photovoltaic applications," Chen said. "With our growth method, we can lock the material's crystal structure with that of the substrate to prevent this phase transition and enhance its phase stability."
In future studies, the researchers will explore what new properties and functionalities they can strain engineer into perovskites using their method. They will also work on scaling up their process to grow large, single-crystalline thin films for industrial applications.
Paper title: "Strain engineering and epitaxial stabilization of halide perovskites." Co-authors include Yuheng Li, Yugang Yu, Jinze Cai, Yue Gu, Chunfeng Wang, Woojin Choi, Hongjie Hu, Chonghe Wang, Yang Li, Jiawei Song, Jingxin Zhang, Baiyan Qi, Muyang Lin, Zuorui Zhang, Shadi Dayeh, Kesong Yang and Yu-Hwa Lo, UC San Diego; Ming-Hui Chiu and Lain-Jong Li, King Abdullah University of Science and Technology, Kingdom of Saudi Arabia; and Rahul Rao, Ahmad E. Islam and Benji Maruyama, Air Force Research Laboratory, Wright Patterson Air Force Base.
This work was supported by UC San Diego startup funds. This work was performed in part at the San Diego Nanotechnology Infrastructure (SDNI) at UC San Diego, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (grant ECCS-1542148).
Liezel Labios | EurekAlert!
What's in your water?
29.01.2020 | Johns Hopkins University
MTU engineers examine lithium battery defects
27.01.2020 | Michigan Technological University
A multidisciplinary team of engineers and scientists has developed a new class of filtration membranes for a variety of applications, from water purification to small-molecule separations to contaminant-removal processes, that are faster to produce and higher performing than current technology. This could reduce energy consumption, operational costs and production time in industrial separations.
Led by Manish Kumar, associate professor in the Cockrell School of Engineering at The University of Texas at Austin, the research team describes their new...
Researchers from Dresden and Osaka present the first fully integrated flexible electronics made of magnetic sensors and organic circuits which opens the path towards the development of electronic skin.
Human skin is a fascinating and multifunctional organ with unique properties originating from its flexible and compliant nature. It allows for interfacing with...
Researchers of the Carl Gustav Carus University Hospital Dresden at the National Center for Tumor Diseases Dresden (NCT/UCC), together with an international...
A Duke University research team has identified a new function of a gene called huntingtin, a mutation of which underlies the progressive neurodegenerative...
For years, a new synthesis method has been developed at TU Wien (Vienna) to unlock the secrets of "strange metals". Now a breakthrough has been achieved. The results have been published in "Science".
Superconductors allow electrical current to flow without any resistance - but only below a certain critical temperature. Many materials have to be cooled down...
16.01.2020 | Event News
15.01.2020 | Event News
07.01.2020 | Event News
29.01.2020 | Earth Sciences
29.01.2020 | Power and Electrical Engineering
29.01.2020 | Agricultural and Forestry Science