International researchers led by Assoc Prof Chris McNeill’s group at Monash University have used an X-ray scattering at the Australian Synchrotron to understand how microstructure contributes to the performance of an organic solar cell made with a semiconducting polymer and fullerene thin film.

The investigators evaluated the performance, microstructure and photophysics of dual stack bulk heterojunction (BH) solar cells made with a low bandgap polymer and fullerene thin film in a study published in Advanced Energy Materials.

The research relied on a range of techniques including X-ray scattering, photoluminescence spectroscopy, ultrafast transient absorption spectroscopy and transient photovoltage measurements, to gain a better understanding of how the choice of fullerene acceptor influences microstructure,  photophysics and contribute to device performance.

A bulk heterojunction device is fabricated by coating a blend of two organic semiconductors between two electrodes. Thin films, which are usually less than 100 nanometres thick, offer production advantages for solar cells.

The close blending of materials is required for high performance because photo-generated excitons travel less than 10 nanometres before recombining, with photocurrent generation proceeding through via the dissociation of excitons a material interfaces. Efficient devices therefore require the blend to be optimally structured on the nanoscale.

2-dimensional X-ray scattering patterns of (a) PC61BM, (b) PC71BM and (c) ICBA. (d) line profiles integrated from 2D scattering patterns and (d) fitted parameters.

 

Advanced characterisation techniques are used to understand how microstructure, or morphology, contributes to power conversion efficiency.

Fullerenes act as electron acceptors in a device. Three novel compounds, PC71BM, PC61BM and ICBA were blended with a low band gap polymer, PBDTTT-EFT for the study.

The highest efficiency (9.4%) was found in the blend using the acceptor PC71BM, which also had the highest visible light absorption.

Prof Chris McNeill and collaborators used Synchrotron-based grazing incidence wide angle X-ray scattering (GIWAXS) to determine the molecular orientation of the polymer with respect to the substrate in the bulk of the thin film.  

The GIWAXS measurements provided information about the orientation of polymer crystallites in the bulk, with these crystallites needing to be properly aligned in order for charges to travel through the material more easily.

Resonant soft X-ray scattering was also carried out by co-author Dr Lars Thomsen at the Advanced Light Source at Lawrence Berkley National Laboratory in the US to clarify the structure and purity of domains.

Thomsen, a member the soft x-ray spectroscopy beamline team at the Synchrotron, has undertaken previous collaborations with the McNeill Group on organic electronics.

R-SoXS indicated that one of the blends, PBDTTT-EFT:PC71BM exhibited the largest domain size and highest domain purity, which was thought to facilitate charge separation and transport.

The scattering profiles also provided an indication of the roughness of the interfaces between the domains in the three compounds.

The R-SoXS and other methods suggested that the lower power conversion efficiency of the ICBA compound might be explained by rougher domain interfaces, lower crystallinity and smaller domain size.

Contributors include Dr Wenchao Huang and colleagues at Monash University, Dr Eliot Gann (now at Brookhaven National Lab), researchers from the University of California Los Angeles, the Indian Institute of Technology Bombay and Victoria University of Wellington.

A Monash-led group of geoscientists used the macromolecular crystallography beamline (MX2) Australian Synchrotron to help them determine the atomic structure of a new mineral discovered in a volcanic area of Far Eastern Russia. 

The research, which was published in American Mineralogist by Prof Joel Brugger of Monash and collaborators from Australia and Russia may provide insight into the processes responsible for the geochemical evolution of Earth. 

The authors reported that an analysis of Nataliyamalikite was challenging because of the small size of single crystals, composite nature of larger aggregates and the extreme light sensitivity of the mineral and the surrounding sulfur matrix. 

Nataliyamalikite grains could not be isolated using optical microscopy. 

X-ray powder diffraction measurements on microcrystals of Nataliyamalikite at 100 K indicated that  the structure was orthorhombic. 

The mineral which has only two atoms, thallium and iodide, in the asymmetrical unit cell, is considered to be a distorted version of rock salt.

The beam diameter was reduced to 7.5 nanometres by a collimator at the Australian Synchrotron MX2 micro-focus beamline to match the crystal size of the micro-aggregates of Nataliyamalikite, which were extracted from the amorphous sulfur matrix by focused ion beam scanning electron microscopy.

MX2 beamline scientist Dr Jason Price assisted in processing the beamline data, which was compared with a synthetic equivalent. 

Electron backscatter diffraction at Monash and in Russia confirmed an orthorhombic crystal lattice of the mineral at ambient conditions. 

The thallium-rich Nataliyamalikite forms in high temperature fumaroles, (thermal openings in areas surrounding a volcano) as a component of arsenic and sulfur-rich coating on lava and scoria around the vents.

In the paper, the authors also provided a description of the process that give rise to concentrations of thallium, leading to the formation of Nataliyamalikite.

Read more on the Monash website. 

 

More than 40 science and engineering graduate students, postdoctoral fellows and early career researchers from across the Asia-Oceania region attended the first Asia Oceania Forum (AOF) Synchrotron Radiation School in early June hosted by the ANSTO at the Australian Synchrotron and supported by the Australian Institute of Nuclear Science and Engineering (AINSE). 

The participants, who are interested in pursuing a career in synchrotron radiation-related fields, had the opportunity to attend a range of lectures and take part in practical sessions on six of the ten beamlines at the Australia Synchrotron.

Those who attended the week-long school came from China, Thailand, Japan, Korea, Taiwan, India, Singapore, New Zealand and within Australia to learn more about the theory and applications of synchrotron radiation for a wide range of science and technology research.

“We were greatly pleased by the level of interest in synchrotron technologies, which are proving to be invaluable across a range of applications and delighted to share Australian and international expertise with the group,” said Prof Richard Garrett, Senior Advisor, Strategic Projects, ANSTO, who was Co-Chair of the school with Dr Mike James, Head of Science at the Australian Synchrotron.

Guest lecturers travelled to Australia from South Korea and the US.

In addition to a general introduction to synchrotron radiation, light source, beamlines, and detectors, the curriculum included sessions on the techniques used on the Australian Synchrotron beamlines, such as medical imaging, powder X-ray diffraction, and micro fluorescence.

At the conclusion of the lectures and practical sessions, participants gave presentations based on their beamline investigations. 

“Actual hands on experience with the beamlines is invaluable for planning research projects and understanding the tremendous analytical capabilities of the instruments,” said Dr James.

The Asia Oceania Forum for Synchrotron Radiation Research (AOFSRR) is an association of the eight synchrotron operating and user nations in the Asian region: China, Thailand, Japan, Korea, Taiwan, India, Singapore and Australia,. Its mission is to strengthen regional cooperation in, and to promote the advancement of, synchrotron radiation research. Three additional countries are associate members: New Zealand, Malaysia and Vietnam.

ANSTO has had a close association with the AOFSRR since its inception in 2006, when it operated the Australian Synchrotron Research Program which joined the Forum as a foundation member representing Australia. Since 2012 ANSTO has served as financial manager of the AOFSRR, to facilitate the payment of membership fees by the eight full member nations.

The main activities of the AOFSRR are to organise an annual workshop and an annual synchrotron school. The Japanese SPring8 facility hosted the school, then known as the Cheiron School, from 2007 until 2015. This has now been replaced by the AOF Synchrotron School which will rotate among the 8 member countries. The next school will be held in South Korea, followed by Thailand.