A solar panel for indoor use, reportedly six times more efficient than currently available options, could soon render batteries for remote controls, keyboards, sensors, alarms, and other home electronics obsolete.
While still in the laboratory stage, the international team of scientists behind the technology, led by researchers from the University College London (UCL), reports that recent tests have demonstrated the indoor solar-harvesting technology is also more durable and retains its performance longer than competitive designs, thereby increasing its potential uses and commercial viability.
Traditional silicon-based solar panels have found several commercial and industrial applications. However, their energy conversion efficiency and overall durability often make them less efficient under indoor lighting. More recently, engineers have turned to perovskite-based solar panels, which are more efficient and can be adapted to specific light wavelengths to also convert indoor light. They are also simpler and less expensive to produce.
“The advantage of perovskite solar cells in particular is that they are low-cost – they use materials that are abundant on Earth and require only simple processing,” explained Dr. Mojtaba Abdi Jalebi, Associate Professor at the UCL Institute for Materials Discovery and the senior author of a study detailing the team’s work. “They can be printed in the same way as a newspaper.”
Unfortunately, the inherent limitations of perovskite cells have curtailed their wider adoption. For example, perovskite cells contain tiny defects in their crystalline structure. Engineers refer to these structural imperfections as ‘traps’ because electrons can become trapped in them before the panel has a chance to convert their energy into electricity, which is instead lost as heat. Perovskite traps also contribute to the cell’s degradation over time, leading to a decrease in energy-harvesting efficiency.
To develop an indoor solar panel from perovskite cells that would be powerful enough to charge devices from traditional indoor lighting, Jalebi and colleagues decided to optimize a perovskite-based cell to have significantly fewer traps. According to the statement announcing the team’s research, they started with a traditional design and then introduced rubidium chloride to encourage “a more homogeneous growth of perovskite crystals with minimal strains.” Ideally, this process would reduce the overall density of electron traps, allowing that energy to be converted to electricity rather than lost as heat.
Next, the team added two chemicals, organic ammonium salts, N-dimethyloctylammonium iodide (DMOAI) and phenethylammonium chloride (PEACl), to the mix. According to the researchers, these two chemicals would, theoretically, “stabilize two types of ions (iodide and bromide ions),” which would prevent them from migrating apart and “bunching” into different structural phases. The team stated that such structural events ultimately degrade the performance of the solar cell over time by “disrupting the flow of charge” through the cell’s material.
As hoped, the three-step chemical formula was a success. Lead author Siming Huang, a PhD student at UCL’s Institute for Materials Discovery, said their process was able to effectively reassemble solar cell traps, which had been “cut up like a cake cut into pieces,” thereby increasing their energy conversion efficiency.
“Through a combination of strategies, we have put this cake back together again, allowing the charge to pass through it more easily,” Huang explained. “The three ingredients we added had a synergistic effect, producing a combined effect greater than the sum of the parts.”
After successfully creating an indoor solar perovskite cell with significantly fewer electron traps, the team tested its energy conversion efficiency. According to the team’s statement, the new solar cells converted 37.6% of indoor light at 1000 lux, “which is equivalent to a well-lit office,” into usable electricity. The team stated this conversion rate is “a world record for this type of solar cell optimised for indoor light, that is with a bandgap of 1.75 eV (electron volts).”
“The bandgap represents the minimum energy required to excite an electron so that it joins the electrical charge through the solar cell,” they explain. “A bandgap of 1.75 eV is tuned to absorb the higher-energy, mostly visible wavelengths of light emitted from indoor sources.”
Next, the team tested the durability of their indoor solar panel under various simulated operating conditions. The first test, which lasted “more than 100 days,” showed the cells retained 92% of their initial conversion rate compared to a control set of cells whose traps had not been reduced. Those control cells only retained 76% of their original performance.
The team’s second test of the treated cells involved 300 hours of “continuous intense light” at a steady 55 °C. As expected, tests showed that the untreated control cells had dropped to 47% of their original efficiency, whereas the new design had retained 76% of its initial energy-conversion performance.
The team said their indoor solar panel’s design is about “six times more efficient” than the best commercially available indoor solar panels. They also suggest indoor solar panels made with these cells could provide usable energy for up to five years, “rather than just a few weeks or months.”
“Currently, solar cells capturing energy from indoor light are expensive and inefficient,” Jalebi explained. “Our specially engineered perovskite indoor solar cells can harvest much more energy than commercial cells and is more durable than other prototypes.”
The researcher also stated that his level of conversion efficiency “paves the way” for everyday electronic devices “powered by the ambient light already present in our lives.”
In the study’s conclusion, the team outlines the increase in energy-dependent indoor technologies and the inability to power all these devices with a battery to meet that demand.
“Billions of devices that require small amounts of energy rely on battery replacements – an unsustainable practice,” Jaleb said. “This number will grow as the Internet of Things expands.”
Although the technology has only been demonstrated in a lab setting, the researcher noted that they are already discussing the technology with potential industry partners “to explore scale-up strategies and commercial deployment.”
The article “Enhancing Indoor Photovoltaic Efficiency to 37.6% Through Triple Passivation Reassembly and n-Type to p-Type Modulation in Wide Bandgap Perovskites” was published in Advanced Functional Materials.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.
