Solar cells have long been associated with harnessing the sun’s energy outdoors, but recent advancements are bringing this technology inside. Breakthroughs in materials and designs are enabling solar cells to efficiently convert indoor light into electricity, opening up new possibilities for powering small devices and reducing reliance on batteries. Recent research highlights significant progress in this field, with some solar cells achieving efficiencies as high as 38% under low indoor light conditions.
The Rise of Indoor Photovoltaics
Indoor photovoltaics (IPV), also known as indoor solar panels, leverage conventional photovoltaic technology but instead of sunlight, they use energy from artificial light sources. These light sources include light-emitting diodes (LEDs), compact fluorescent lamps (CFLs), and halogen lamps. IPVs are tested using indoor light simulators, often solar simulators with a modified spectrum to mimic indoor light sources.
The growing demand for self-powered microelectronic indoor devices, such as sensors, smart meters, wearable devices, and actuators, is driving the development of IPV technology. These devices automate daily activities through the Internet of Things (IoT), making IPV a crucial component in their functionality.
Key Benefits of Indoor Solar Cells
- Sustainability: Reduces the need for disposable batteries, promoting a more sustainable future.
- Convenience: Provides continuous power for devices, eliminating the need for frequent charging or battery replacements.
- Versatility: Can be integrated into various devices, including IoT sensors, wearable fitness monitors, home security sensors, and low-power electronics.
- Efficiency: Emerging materials and designs are significantly increasing the power conversion efficiency of indoor solar cells.
Innovative Materials and Designs
Several innovative approaches are contributing to the improved efficiency of indoor solar cells. These include the use of perovskite materials, organic semiconductors, and transition metal dichalcogenides (TMDs).
Perovskite Solar Cells
Perovskite compounds, often synthesized in laboratories, are proving to be more effective at converting light into electricity compared to traditional materials like silicon. These materials excel at absorbing visible light and efficiently converting it into energy. An Australian-Korean research team working with Macquarie University has developed a perovskite solar cell that achieves record-breaking power conversion efficiencies in low-light indoor environments. This technology incorporates two innovative components:
- Perovskite Material: Instead of silicon, perovskite is used to generate electricity.
- Aluminum Layer: An aluminum layer reduces energy leaks, further enhancing efficiency.
These perovskite solar modules have demonstrated power densities three to five times greater than commercially available photovoltaic cells for indoor use. In well-lit indoor environments, they have achieved power conversion efficiencies of up to 33.5% and a record-breaking power density of 107.3 milliwatts per square centimeter.
Organic Photovoltaics (OPV)
OPVs utilize semiconducting polymers to convert light into electricity. These materials offer a sustainable, eco-friendly, lightweight, and flexible alternative to traditional silicon-based cells. Recent advancements have pushed OPV efficiency close to 20% on a small-cell level, making them competitive with conventional PV technologies. Researchers are also exploring high bandgap organic semiconductors to further enhance energy conversion under indoor lighting conditions.
Transition Metal Dichalcogenides (TMDs)
Researchers at Stanford University have explored the potential of TMD solar cells for indoor energy harvesting. TMDs, such as WSe2 and MoS2, are two-dimensional materials with exceptional semiconducting properties and high optical absorption coefficients. These materials are suitable for producing semi-transparent and flexible solar cells, making them ideal for applications in aerospace, architecture, electric vehicles, and wearable electronics.
Studies suggest that TMD solar cells can achieve power conversion efficiencies of up to 36.5% under indoor lighting. With improved material quality and optimized designs, TMD solar cells could outperform commercial indoor photovoltaic technologies, offering a sustainable energy solution for the expanding IoT ecosystem.
Other Materials and Technologies
- Gallium Indium Phosphide (GaInP): This material has demonstrated high efficiency under indoor light, converting nearly 40% of light energy into electricity. However, its performance under sunlight is less impressive due to its large band gap.
- Dye-Sensitized Solar Cells (DSSCs): DSSCs are already available for indoor applications due to their high efficiency under low-intensity light.
- Quantum Dot Solar Cells (QDSCs): These cells can be engineered to absorb different wavelengths of light, offering greater potential than silicon. Recent research shows QDSCs achieving 19.1% efficiency in lab environments.
Maximizing Solar Panel Efficiency in Low Light
Several strategies can be employed to maximize the efficiency of solar panels in low-light conditions:
- Concentrated Photovoltaic Technology: Lenses or mirrors concentrate sunlight onto small, high-efficiency solar cells, achieving efficiency levels greater than 40%.
- Optimal Orientation and Tilt: Adjusting the tilt angle of panels towards the sun’s path can significantly enhance energy output in low-light intensity regions.
- Energy Storage Solutions: Battery storage systems store excess energy produced during maximum sunlight exposure for consumption during nighttime or low-light conditions.
- Low-Light Performance Panels: Selecting solar panels specifically designed for low-light performance, typically varying between 15% and 22% efficiency, ensures energy generation even in dim conditions.
Challenges and Future Directions
Despite the significant progress, several challenges remain in the development of indoor solar cells:
- Material Quality: Improving the quality of materials like perovskites and TMDs is crucial for achieving higher efficiencies and long-term stability.
- Cost Reduction: Lowering the production costs of advanced materials and manufacturing processes is essential for widespread adoption.
- Durability and Stability: Enhancing the durability and stability of indoor solar cells is necessary to ensure reliable performance over extended periods.
- Optimization for Specific Light Sources: Tailoring solar cells to specific indoor light sources, such as LEDs or fluorescent lamps, can further improve their efficiency.
The future of indoor solar cells looks promising, with ongoing research focused on addressing these challenges and unlocking the full potential of this technology. As materials and designs continue to advance, indoor solar cells are poised to play a significant role in powering our devices and creating a more sustainable future.
Applications of Indoor Solar Cells
Indoor solar cells have a wide range of potential applications, including:
- Internet of Things (IoT) Devices: Powering sensors, smart home devices, and other IoT devices, reducing the need for batteries and enabling self-sustaining operation.
- Wearable Electronics: Integrating into wearable fitness monitors, smartwatches, and other wearable devices, providing continuous power and eliminating the need for frequent charging.
- Low-Power Consumer Electronics: Powering devices like remote controls, wireless keyboards, calculators, and other low-power electronics, reducing reliance on disposable batteries.
- Smart Buildings: Integrating into building management systems, powering sensors and controls for lighting, HVAC, and security systems.
- Aerospace and Electric Vehicles: Utilizing lightweight and flexible solar cells in aerospace applications and electric vehicles, improving energy efficiency and reducing weight.
The Push for Standardization
The IEC introduced new specifications in 2023 for evaluating photovoltaics under indoor light. These standards detail the testing process and light source calibration, considering both device and light source dependencies. The standards include calibrated light sources for standard fluorescent lights and cool LEDs, with a color temperature of 5000 K and illuminance levels of 1000 lx, 200 lx, and 50 lx.
Powerfoyle Technology
Exeger has developed a solar cell technology called Powerfoyle™, which transforms any kind of light, indoor or outdoor, into electrical power. Powerfoyle is designed to be flexible and customizable, allowing seamless integration into various products. This technology offers high performance in both indoor and outdoor light conditions, providing a sustainable and convenient energy solution. Devices using Powerfoyle can continuously charge using ambient light, eliminating the need for battery changes or charging cables.
Epishine’s Lamination Process
Epishine has developed a patented lamination process that ensures high performance in indoor solar cells, even under low light conditions. By printing half the solar cell on each substrate, drying the films, and then laminating them together, the risk of conductive materials filling voids in the semiconducting active layer is eliminated. This process maintains high conversion efficiency and enhances the reliability of indoor solar cells.
Conclusion: Lighting the Way to a Sustainable Future
Breakthroughs in solar cell technology are paving the way for efficient indoor energy harvesting. With efficiencies reaching 38% in low indoor light, these advancements promise to revolutionize how we power our devices and reduce our dependence on traditional energy sources. As research continues and new materials emerge, indoor solar cells are poised to play an increasingly important role in creating a more sustainable and energy-efficient future.
