As the cost of solar energy drops and electric rates rise, solar is getting much closer to grid parity. At the same time, efficiencies are going up in tiny increments, thanks to innovative and varied research underway around the world. For example, bio-mimicry-themed studies use plants and butterflies as the basis of new designs; stretchy coatings can put solar on clothing; lead-free designs reduce the toxic substances in solar cells; and light is found to heal defects in perovskite. We’ve selected five significant research projects that take different approaches, each of which is doing its part to incrementally advance solar.
Texture of Flower Petals Inspires Solar Cell Coating
Researchers in Germany studied the texture of the viola wittrockiana flower, which has a hierarchical surface texture consisting of micro- and nano-features, which together lead to excellent light-harvesting properties.
They developed a photoresist coating that they imprinted on the surface of sola cells and found that due to a retro-reflection effect, light that is reflected is captured and redirecteds back to the solar cell. The next step in the research is to study the soiling and self-cleaning aspects of the textures, as well as to optimize the coating to withstand outdoor conditions. They are also looking into how to upscale the texture through hot embossing or roll-to-roll manufacturing techniques.
Disordered Structure of Butterfly Wing Inspires New Solar Cell Design
A new design for a solar cell was inspired by the patterning of the black butterfly’s wings.
Just as on the butterfly wings, the patterns on the photovoltaic thin-film absorbing layer has nanoholes with varying diameters arranged in a disordered way. The disordered configuration enables the PV devise to efficiently harvest the light over a broad spectral range. The next step in their research is to test different types of photovoltaic absorbers to demonstrate that it has universal application.
Washable, Stretchable Organic Photovoltaics for Wearable Electronics
Researchers in Japan have developed a new type of ultrathin, flexible organic solar cell that is coated on both sides with elastomers to make it stretchable and waterproof.
Wearable devices have to be able to move with the movement of the human body, and endure all kinds of weather conditions—so the researchers put these cells to the test. They found that the cells can be soaked in water or compressed to nearly half its size, repeatedly, and it maintains nearly all of its efficiency. The next step in the research is to improve both the energy conversion efficiency and long-term stability. Potential applications are textile-compatible power sources to operate the sensors or other devices.
Bismuth: A non-toxic lead alternative in solar cells
Lead-based hybrid halide perovskites offer great hope for a new generation of cheap, easy-to-produce solar cells. However, the lead content could prevent their wide-spread use.
A group of researchers in the UK has shown that bismuth could be a non-toxic alternative to lead in perovskite solar cells. They found that bismuth is stable in air for nearly 200 days and it is also defect tolerant, and in testing the theoretical limit for this material was found to be 22%, which is comparable to traditional silicon and perovskite solar cells. The next step in the research is to improve the collection of carriers in order to improve efficiency.
Illumination, Oxygen Plus Humidity Permanently Heals Defects in Perovskites
Tiny defects in the crystalline structure of perovskites has been preventing perovskites of superstar status, but an international team of researchers discovered that light, plus oxygen and humidity can cure defects in the molecular structure of halide perovskites.
Using just light can move the iodide ions away, weeping away most of the defects in the region with them. But when the light is removed, the ions—along with the defects—migrate right back. In more recent studies, the team introduced atmospheric molecules, including oxygen and water. They found that, under light, this method leads to the passivation of defects. The next step in the research is to get to 100% luminescence efficiency without voltage loss. Once achieved, their method may be applied in perovskite solar cells, LEDs and lasers.
