Semiconductor breakthrough paves way for “inexpensive and nearly invisible” solar panels

Scientists have achieved a breakthrough in organic solar panel technology that could allow the power source to become a ubiquitous presence in our lives, with the ability to be churned out cheaply by manufacturers and laminated to almost any surface you can think of.

Organic solar cells, while far cheaper than the more widespread inorganic equivalents that are most commonly seen in stores and rooftops today, have traditionally had very poor conductivity, meaning they can only generate small amounts of power.

However, engineers at the University of Michigan have changed that, by developing a way to make the electrons found in organic solar cells’ semiconductors travel far further, greatly improving their conductivity and thus their ability to generate power.

As a result, the breakthrough could make organic solar cells a viable alternative to inorganics for the first time, with the added benefit that they are far cheaper to manufacture, meaning they could see far more widespread use than is currently the case.

The research, which was published today in Nature, initially began as an experiment by Stephen Forrest, the Peter A. Franken Distinguished University Professor of Engineering and Paul G. Goebel Professor of Engineering at the University of Michigan, into organic solar architecture using a technique called vacuum thermal evaporation.

This involved Forrest and his team applying a thin film made up of 60 carbon atoms – known as a fullerene layer – over an organic cell’s power-producing later, where the sun’s photons displace electrons from their associated molecules, forming the basis of the power supply. On top of this they added another film of carbon atoms, which was designed to keep the electrons from escaping.

But this action produced a rather unexpected result. Instead of behaving as predicted, the electrons were moving at random through the material, even beyond the confines of the power-generating area, something that had never been observed in organic cells before.

This became the focus of their research, and after months of work they determined the cause: the layer of electrons was creating an area of low energy known as an energy well where negatively charged electrons could not recombine with the power-producing layer, and so moved far further than was normally the case.

“You can imagine an energy well as sort of a canyon–electrons fall into it and can’t get back out,” said Caleb Cobourn, a graduate researcher in the University of Michigan Department of Physics and an author on the study. “So they continue to move freely in the fullerene layer instead of recombining in the power-producing layer, as they normally would. It’s like a massive antenna that can collect an electron charge from anywhere in the device.”

said Quinn Burlingame, an electrical engineering and computer science graduate researcher and author on the study, with the original experiment. Image courtesy of Robert Coelius/Michigan Engineering, Communications & Marketing

While the research is still in the early stages, this breakthrough is hugely significant, and could be used to develop ultra-cheap, near-invisible solar panels in the future.

“This discovery essentially gives us a new knob to turn as we design organic solar cells and other organic semiconductor devices,” said Quinn Burlingame, an electrical engineering and computer science graduate researcher and author on the study. “The possibility of long-range electron transport opens up a lot of new possibilities in device architecture.”

It could even eventually play a vital role in the shift to renewable energy supplies.

“I believe that ubiquitous solar power is the key to powering our constantly warming and increasingly crowded planet, and that means putting solar cells on everyday objects like building facades and windows,” Forrest said. “Technology like this could help us produce power in a way that’s inexpensive and nearly invisible.”

Soviet report detailing lunar rover Lunokhod-2 released for first time

Russian space agency Roskosmos has released an unprecedented scientific report into the lunar rover Lunokhod-2 for the first time, revealing previously unknown details about the rover and how it was controlled back on Earth.

The report, written entirely in Russian, was originally penned in 1973 following the Lunokhod-2 mission, which was embarked upon in January of the same year. It had remained accessible to only a handful of experts at the space agency prior to its release today, to mark the 45th anniversary of the mission.

Bearing the names of some 55 engineers and scientists, the report details the systems that were used to both remotely control the lunar rover from a base on Earth, and capture images and data about the Moon’s surface and Lunokhod-2’s place on it. This information, and in particularly the carefully documented issues and solutions that the report carries, went on to be used in many later unmanned missions to other parts of the solar system.

As a result, it provides a unique insight into this era of space exploration and the technical challenges that scientists faced, such as the low-frame television system that functioned as the ‘eyes’ of the Earth-based rover operators.

A NASA depiction of the Lunokhod mission. Above: an image of the rover, courtesy of NASA, overlaid onto a panorama of the Moon taken by Lunokhod-2, courtesy of Ruslan Kasmin.

One detail that main be of particular interest to space enthusiasts and experts is the operation of a unique system called Seismas, which was tested for the first time in the world during the mission.

Designed to determine the precise location of the rover at any given time, the system involved transmitting information over lasers from ground-based telescopes, which was received by a photodetector onboard the lunar rover. When the laser was detected, this triggered the emission of a radio signal back to the Earth, which provided the rover’s coordinates.

Other details, while technical, also give some insight into the culture of the mission, such as the careful work to eliminate issues in the long-range radio communication system. One issue, for example, was worked on with such thoroughness that it resulted in one of the devices using more resources than it was allocated, a problem that was outlined in the report.

The document also provides insight into on-Earth technological capabilities of the time. While it is mostly typed, certain mathematical symbols have had to be written in by hand, and the report also features a number of diagrams and graphs that have been painstakingly hand-drawn.

A hand-drawn graph from the report, showing temperature changes during one of the monitoring sessions during the mission

Lunokhod-2 was the second of two unmanned lunar rovers to be landed on the Moon by the Soviet Union within the Lunokhod programme, having been delivered via a soft landing by the unmanned Luna 21 spacecraft in January 1973.

In operation between January and June of that year, the robot covered a distance of 39km, meaning it still holds the lunar distance record to this day.

One of only four rovers to be deployed on the lunar surface, Lunokhod-2 was the last rover to visit the Moon until December 2013, when Chinese lunar rover Yutu made its maiden visit.