Super thin photovoltaic devices underpin solar technology and gains in the efficiency of their production are therefore keenly sought. KAUST researchers have combined and rearranged different semiconductors to create so-called lateral p-n heterojunctions--a simpler process they hope will transform the fabrication of solar cells, self-powered nanoelectronics as well as ultrathin, transparent, flexible devices.
Two-dimensional semiconductor monolayers, such as graphene and transition-metal dichalcogenides like WSe2 and MoS2, have unique electrical and optical properties that make them potential alternatives to conventional silicon-based materials.
Recent advances in material growth and transfer techniques have allowed scientists to manipulate these monolayers. Specifically, vertical stacking has led to ultrathin photovoltaic devices but requires multiple complex transfer steps. These steps are hampered by various issues, such as the formation of contaminants and defects at the monolayer interface, which limit device quality.
"Devices obtained using these transfer techniques are usually unstable and vary from sample to sample," says lead researcher and former visiting student of Associate Professor, Jr-Hau He, Meng-Lin Tsai, who adds that transfer-related contaminants significantly affect device reliability. Electronic properties have also proven difficult to control by vertical stacking.
To fully harness the exceptional properties of these two-dimensional materials, Tsai's team, under the mentorship of He, created monolayers featuring lateral WSe2-MoS2 heterojunctions and incorporated them into solar cells. Under simulated sunlight, the cells achieved greater power conversion efficiency than their vertically stacked equivalents.
To do this, first the researchers synthesized the heterojunctions by consecutively depositing WSe2 and MoS2 on a sapphire substrate. Next, they transferred the materials onto a silicon-based surface for photovoltaic device fabrication.
High-resolution microscopy revealed that the lateral junction displayed a clear separation between the semiconductors at the interface. Also, the researchers detected no discernable height difference between semiconductor regions, consistent with an atomically thin interface.
These interfacial characteristics signaled success. "Our structures are cleaner and more ideal than vertically stacked assemblies because we didn't need the multi-step transfer procedure," explains Tsai.
Furthermore, the lateral heterojunctions mostly retained their efficiency despite changes to the orientation of the incident light. Being able to take light coming from any direction means expensive solar tracking systems will become redundant.
According to Tsai, the implementation of lateral heterojunctions in more complex circuits and interconnects may result in higher performance than in conventional solar cells and so the team is working on the next steps. "We are trying to understand the underlying kinetics and thermodynamics of these heterojunctions to design more efficient cells," he adds.
Carolyn Unck | EurekAlert!
From foam to bone: Plant cellulose can pave the way for healthy bone implants
19.03.2019 | University of British Columbia
Additive printing processes for flexible touchscreens: increased materials and cost efficiency
19.03.2019 | INM - Leibniz-Institut für Neue Materialien gGmbH
DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.
The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...
Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.
The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...
Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.
Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.
A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...
Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.
"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...
11.03.2019 | Event News
01.03.2019 | Event News
28.02.2019 | Event News
22.03.2019 | Life Sciences
22.03.2019 | Life Sciences
22.03.2019 | Information Technology