Indoor photovoltaics have gained significant attention due to the growing demand for self-powered Internet of Things (IoT) devices, smart sensors, and low-energy electronics. Traditional solar cells optimized for outdoor sunlight perform poorly under indoor lighting conditions due to the mismatch between their absorption spectra and the emission spectra of artificial light sources. In contrast, quantum dot-based photovoltaic devices exhibit unique advantages for indoor light harvesting, including tunable bandgaps, high absorption coefficients, and efficient charge carrier extraction under low illumination.
The spectral output of common indoor lighting sources such as light-emitting diodes (LEDs), fluorescent lamps, and incandescent bulbs differs substantially from natural sunlight. LED lighting, which dominates modern indoor environments, emits narrow bands in the visible spectrum with peaks between 450 nm and 650 nm, while fluorescent lights produce discrete emission lines from mercury vapor and phosphors. Incandescent bulbs offer a broad but weak emission skewed toward the infrared. Quantum dots can be engineered to align with these specific spectra by adjusting their size and composition, allowing for optimal light absorption. For instance, cadmium selenide (CdSe) quantum dots with diameters tuned between 2 nm and 6 nm exhibit absorption edges from 500 nm to 650 nm, closely matching the dominant wavelengths of indoor lighting.
Under low-light conditions typical of indoor environments (100–1000 lux), quantum dot solar cells demonstrate superior performance compared to conventional silicon and thin-film photovoltaics. Their high extinction coefficients enable efficient photon capture even at low intensities, while their multiple exciton generation potential enhances charge carrier production. Studies have shown that lead sulfide (PbS) quantum dot solar cells achieve power conversion efficiencies exceeding 12% under LED illumination at 200 lux, whereas silicon cells often drop below 5% under the same conditions. The open-circuit voltage of quantum dot devices also shows less sensitivity to light intensity variations, making them more reliable for consistent energy harvesting in dim environments.
The design of quantum dot solar cells for indoor applications involves careful optimization of the active layer, charge transport layers, and electrodes. Colloidal quantum dots are typically deposited as thin films via solution processing, enabling low-cost fabrication compatible with flexible substrates. To minimize recombination losses, organic ligands on quantum dot surfaces are exchanged or treated to improve carrier mobility. Electron transport layers such as zinc oxide (ZnO) and hole transport layers like poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) are commonly used to facilitate charge extraction. Thin, semi-transparent electrodes such as indium tin oxide (ITO) or silver nanowires maintain sufficient conductivity while allowing maximum light penetration.
One critical advantage of quantum dot photovoltaics is their ability to maintain performance under non-ideal angles of light incidence, which is common for indoor devices that may not always face light sources directly. Their high absorption cross-section ensures reasonable efficiency even under oblique lighting, unlike traditional solar cells that suffer significant losses when not aligned perpendicularly to the light source. Additionally, quantum dot solar cells exhibit minimal performance degradation over time under indoor conditions, as they are not subjected to the ultraviolet radiation and thermal cycling that degrade outdoor solar panels.
Applications in IoT devices benefit greatly from the integration of quantum dot solar cells. Wireless sensor nodes, wearable health monitors, and smart home devices require microwatt to milliwatt power levels, which can be sustainably supplied by indoor light harvesting. For example, a temperature and humidity sensor powered by a 1 cm² quantum dot solar cell under 500 lux LED lighting can operate continuously without batteries, reducing maintenance and environmental waste. The flexibility and lightweight nature of quantum dot films also enable integration into curved surfaces and portable electronics.
Stability and environmental considerations remain important factors in the development of quantum dot solar cells for indoor use. Heavy metal-based quantum dots like CdSe and PbS pose toxicity concerns, prompting research into alternative materials such as indium phosphide (InP) and silicon quantum dots. Encapsulation techniques using polymers or inorganic barriers prevent moisture and oxygen ingress, extending device lifetimes. Accelerated aging tests indicate that properly encapsulated quantum dot solar cells retain over 80% of their initial efficiency after 10,000 hours of continuous indoor operation.
Future advancements in quantum dot solar cells for indoor applications may focus on further improving efficiency through bandgap engineering, reducing reliance on toxic materials, and scaling up manufacturing processes. The combination of tailored absorption profiles, robust low-light performance, and compatibility with flexible electronics positions quantum dot photovoltaics as a leading solution for powering the next generation of autonomous IoT devices. As indoor energy harvesting technologies mature, they will play a pivotal role in enabling sustainable, battery-free electronics for smart buildings, industrial monitoring, and personal healthcare systems.
The following table summarizes key performance metrics of quantum dot solar cells under different indoor lighting conditions:
Light Source | Illuminance (lux) | Power Conversion Efficiency (%) | Open-Circuit Voltage (V)
LED (450–650 nm) | 200 | 12.1 | 0.52
LED (450–650 nm) | 500 | 14.3 | 0.55
Fluorescent (discrete peaks) | 300 | 10.7 | 0.48
Incandescent (broad IR) | 200 | 8.2 | 0.45
These values highlight the adaptability of quantum dot solar cells to various indoor lighting environments, making them a versatile solution for low-power electronics. With continued optimization, their efficiency and reliability will further improve, enabling broader adoption in energy-autonomous devices.