Solar Research Trends 2012

Applications Research Top Solar Research Trends 2012
Cost cutting and negative operating results dominated the picture of PV manufacturing around the globe last year. Despite all cost pressure, or maybe even just because of it, research went on even in the difficult market environment of 2012, and has created a number of breakthroughs in many disciplines of PV manufacturing and performance. We looked at the top 10 most-read research articles on Solar Novus Today in 2012 to spot the important trends.

Flexible thin-film research

Despite all cost pressure, or maybe even just because of it, research went on even in the difficult market environment of 2012.

Despite on-going research in the crystalline world, R&D massively takes place in other PV technology sectors. Last summer, scientists at the University of Toronto, Canada, and the King Abdullah University of Science & Technology (KAUST) in Saudi Arabia reported that they collaboratively have created a colloidal quantum dot (CQD) thin-film solar cell with a certified world-record efficiency of 7%. (See “Quantum Dot Solar Cell Achieves World Record Efficiency”).The 37% increase over the previous certified world record was made possible by a technical advance called “hybrid passivation scheme”. The breakthrough could further pave the way for inexpensive, fast mass production of thin-film solar technologies as it offers the possibility of creating solar cells on flexible substrates, using “roll-to-roll” manufacturing in the same way that newspapers are printed in mass quantities.

A method that can also be used to produce organic photovoltaic (OPV) cells developed for instance by energy company Phillips 66 in collaboration with South China University of Technology (SCUT) and California start-up Solarmer Energy Inc. The article “Phillips-66 Creates World Record OPV Cell with 9.31% Efficiency” describes research that resulted in a new world record last year for energy conversion efficiency in this category. At the same time, an interdisciplinary group of researchers from the University of California Los Angeles (UCLA) developed a high-performance polymer solar cell (PSC) that is highly transparent in the visible light range and produces energy by absorbing near-infrared and infrared radiation from the solar spectrum. These lightweight, flexible PSCs made from photoactive plastic-like materials are nearly 70% transparent to the human eye, because they mainly use near-infrared and infrared radiation  (See “Highly Transparent Polymer Cell Converts Near-Infrared Solar Radiation”.)

Material research

A possible way to drive down material and manufacturing costs was presented by researchers at the North Carolina State University (NCSU) in Raleigh, North Carolina (US), who may have found a way to significantly enhance solar absorption using sandwiched nanostructures. The article “Thinner, Cheaper Solar Cells with Sandwiched Nanostructures” describes a technique that would enable manufacturers to produce much thinner, thus, much cheaper, solar cells in less time while maintaining or even improving conversion efficiency. The new production process would even be compatible with existing manufacturing processes of thin-film solar cells in the industry.

Another result in thin-film research was presented by researchers at the Agency for Science, Technology and Research (A*STAR) in Singapore who may have found a way to reduce the cost of dye-sensitized solar cells (DSSC) by replacing indium tin oxide (ITO) electrodes with a thin film of carbon nanotubes. The article “Carbon Nanotube Thin Film Could Drive Down Cost of Dye-Sensitized Solar Cells”, describes what scientists believe could lead to the emergence of truly flexible solar cells. Transparent conductive oxides like ITO are state-of-the-art technology for window electrodes. However, they are brittle and the most expensive part of DSSC. Plus, indium is scarce. By contrast, carbon-based materials could have significantly lower cost, due to the abundant material source and potentially scalable fabrication.

Cell efficiency

In an effort to raise cell efficiency, scientists at the US Department of Energy’s National Renewable Energy Laboratory (NREL) together with Natcore Technology, Inc. have created the “blackest” solar cell to date, a black silicon solar cell that absorbs 99.7% of the sunlight. In this collaborative project, described in “Blackest Solar Cell Absorbs 99.7% Sunlight,” the researchers are aiming at reducing the cost of silicon solar cells by about 2 to 3% while increasing energy output from 3% to 10% over the course of a day without a tracking mechanism. Black silicon solar cells can potentially get higher solar energy conversion efficiency since they reflect less light. Furthermore, black silicon as an anti-reflection technology costs much less than conventional anti-reflection technologies that don’t use liquid etches.

Another, still more fundamental research project at NREL concentrated on the first solar cell that produces a photocurrent with external quantum efficiency (the spectrally resolved ratio of collected charge carriers to incident photons) greater than 100%, though applying a process called Multiple Exciton Generation (MEG)—or Carrier Multiplication (CM)—as the key to achieving a peak quantum efficiency of 114%, where a single absorbed photon bearing at least twice the bandgap energy can produce two or more electron-holes. This research is highlighted in “NREL Creates What May be Third-Generation Solar Cell.”

CPV finally going large scale

Research on concentrating PV (CPV) has made a big step forward in efficiency last year. CPV pioneers Dr. Andreas Bett, Fraunhofer ISE and Hansjörg Lerchenmüller, Soitec Solar GmbH have been awarded with the German Environmental Award for their groundbreaking achievements. Research on CPV continued all over the world: The US Department of Energy's (DOE) National Renewable Energy Laboratory (NREL) with industrial partner Solar Junction developed a SJ3 solar cell that uses tunable bandgaps, lattice-matched architecture and ultra-concentration tunnel junctions to achieve a world-record conversion efficiency of 43.5% with potential to reach 50% ().

Storage solutions

Research on the storage solutions for renewable energy – one of the main drivers in the industry last year – continued, as well. Materials scientists at Rice University in Houston, Texas (US) have developed a rechargeable lithium-ion battery that can be painted on virtually any surface. The new fabrication technique, described in “Paintable Battery Works with Solar Cells,” would open the door to new design and integration possibilities for storage devices. The technology developed by Rice could one day enable standalone hybrid devices for capturing and storing solar energy.

Duke University researchers analyzed a hybrid system in which sunlight heats a mixture of water and methanol in a maze of tubes on a rooftop. After two catalytic reactions, the system produces hydrogen that can be stored and used on demand in fuel cells. The set-up allows up to 95% of the sunlight to be absorbed with very little being lost as heat to the surroundings.

All these research achievements show that the technological progress of PV continues to advance. Even with the burden of rapidly decreasing crystalline PV, through intensive research also other disciplines and technologies still have their chance to emerge end become competitive.