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Author: Andrew Myers, Stanford University

There is a race going on in the field of solar engineering to create thin and flexible solar panels that are almost impossible. Engineers imagine their use in mobile applications, from self-powered wearable devices and sensors to light aircraft and electric vehicles. In this context, Stanford University researchers have achieved record efficiencies in a group of promising photovoltaic materials.

Compared with other solar materials, the main advantage of these transition metal dichalcogenides (or TMDs) is that they absorb the extremely high levels of sunlight that hit their surfaces.

Koosha Nassiri Nazif, a PhD student in electrical engineering at Stanford University and co-lead author of the study, said: “Imagine an autonomous drone with a thinner than a piece of paper installed on the top of the wing. 15 times the solar array to power itself.” December 9th edition of Nature Communications. "This is TMD's promise."

The search for new materials is necessary because silicon, the king of solar materials, is too heavy, heavy and rigid for applications where flexibility, light weight and high power are particularly prominent, such as wearable devices and sensors or aerospace and electric vehicles.

"Silicon now accounts for 95% of the solar market, but it is far from perfect. We need new materials that are lightweight, bendable, and frankly, more environmentally friendly," said Krishna Saraswat, a professor of electrical engineering and senior author of the study. Paper.

Although TMD has a bright future, it has been difficult to convert more than 2% of the sunlight absorbed by them into electricity in research experiments so far. For silicon solar panels, this figure is close to 30%. To be widely used, TMD must close this gap.

The new Stanford prototype achieves a power conversion efficiency of 5.1%, but the author predicts that through optical and electrical optimization, they can actually achieve an efficiency of 27%. This number is comparable to the best solar panels on the market today, including silicon.

In addition, the prototype achieves 100 times the power-to-weight ratio of any undeveloped TMD. This ratio is important for mobile applications, such as drones, electric vehicles, and the ability to charge expeditionary equipment on the move. When looking at specific power (a measure of the electrical power output per unit weight of a solar cell), the prototype produced 4.4 watts per gram, a figure comparable to other thin-film solar cells today (including other experimental prototypes).

"We think we can increase this key ratio tenfold through optimization," Saraswat said, adding that they estimate that the actual limit of their TMD battery is 46 watts per gram.

However, their biggest advantage is their remarkable thinness, which not only minimizes material usage and cost, but also makes TMD solar cells light and flexible, and can be molded into irregular shapes-car roofs, Airplane wing or human body. The Stanford team was able to produce active arrays only a few hundred nanometers thick. The array includes photovoltaic TMD tungsten diselenide and gold contacts spanned by a layer of conductive graphene that is only a single atom thick. All of this is sandwiched between a soft skin-like polymer and an anti-reflective coating that improves light absorption.

When fully assembled, the TMD battery is less than 6 microns thick-roughly the thickness of a light office trash bag. It takes 15 layers to reach the thickness of a sheet of paper.

Although thinness, lightness, and flexibility are very desirable goals in themselves, TMD also has other engineering advantages. In the long run, they are stable and reliable. Unlike other challengers of thin-film crowns, TMD does not contain toxic chemicals. They are also biocompatible, so they can be used in wearable applications that require direct contact with human skin or tissue.

Many of the advantages of TMD are offset by certain disadvantages, mainly in the engineering complexity of mass production. The process of transferring the ultra-thin TMD layer to a flexible support material usually damages the TMD layer.

Alwin Daus is the co-lead author of the study with Nassiri Nazif, who designed the transfer process to fix the thin TMD solar cell array to the flexible substrate. He said that this technical challenge is considerable. Daus explained that one of the steps is to transfer an atomically thin layer of graphene to a flexible substrate that is only a few microns thick. He was a postdoctoral scholar in the Eric Pop research group at Stanford University when he was conducting this research. He is currently a senior researcher at Aachen University of Technology in Germany.

This complex process makes the TMD fully embedded in the flexible substrate, thereby improving durability. The researchers tested the flexibility and robustness of their devices by bending them around a metal cylinder less than a third of an inch thick.

"Strong, flexible and durable, TMD is a promising new direction for solar technology," Nassiri Nazif concludes.

Other Stanford University co-authors of this work include Stanford University electrical engineering faculty Eric Pop and Ada Poon; Mark Brogersma Materials Science and Engineering; visiting scholar Sam Vaziri; postdoctoral scholar Raisul Islam; and graduate students Jiho Hong, Nayeun Lee, and Aravindh Kumar , Frederick Nitta, Michelle E. Chen and Siavash Kananian. Further explore translucent and flexible solar cells made of atomic-level thin sheets. For more information: Koosha Nassiri Nazif et al., High specific power flexible transition metal dichalcogenide solar cells, Nature Communications (2021). DOI: 10.1038/s41467-021-27195-7 Journal information: Nature Communications

Stanford University provides a citation: Newly developed solar materials may usher in ultra-thin, lightweight solar panels (December 14, 2021) Retrieved on December 20, 2021 from https://techxplore.com/news/2021-12 -newly-solar-materials-usher -ultrathin.html This document is protected by copyright. Except for any fair transaction for private learning or research purposes, no part may be copied without written permission. The content is for reference only.

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