Indoor light energy harvesting has emerged as a promising technology for powering low-energy electronic devices in smart homes, IoT sensors, and wearable electronics. Unlike traditional solar cells optimized for outdoor sunlight, indoor photovoltaics must operate efficiently under low-intensity, diffuse light from artificial sources such as LEDs and fluorescent lamps. Key materials for this application include organic photovoltaics (OPVs), perovskite solar cells, and dye-sensitized solar cells (DSSCs), each offering unique advantages in efficiency, stability, and integration potential.

Organic photovoltaics are lightweight, flexible, and tunable for absorption in the visible spectrum, making them well-suited for indoor applications. Their bandgap can be engineered to match the emission spectra of common indoor light sources, typically peaking between 400 and 700 nm. Under low-light conditions (200–1000 lux), OPVs have demonstrated power conversion efficiencies (PCE) ranging from 15% to 25%, depending on the active layer composition. For instance, non-fullerene acceptor-based OPVs achieve higher open-circuit voltages and fill factors under dim lighting compared to traditional fullerene derivatives. However, stability remains a challenge due to photo-oxidation and morphological degradation over time. Encapsulation techniques and the development of more robust organic materials have extended operational lifetimes to several thousand hours under continuous indoor illumination.

Perovskite solar cells have gained attention for their exceptional optoelectronic properties, including high absorption coefficients and tunable bandgaps. Methylammonium lead iodide (MAPbI3) and formamidinium lead iodide (FAPbI3) perovskites exhibit PCEs exceeding 30% under indoor light, owing to their low non-radiative recombination losses and high shunt resistance. The ability to process perovskites at low temperatures enables their integration onto flexible substrates, which is advantageous for smart home applications. Despite their high efficiency, perovskite devices face stability issues from moisture, heat, and ion migration. Advances in compositional engineering, such as mixed halide perovskites and 2D/3D heterostructures, have improved humidity resistance while maintaining performance under low-light conditions.

Dye-sensitized solar cells operate on a photo-electrochemical mechanism, where light-absorbing dyes inject electrons into a wide-bandgap semiconductor like TiO2. DSSCs are particularly effective under diffuse light due to their high absorption cross-section and low dependence on incident angle. Ruthenium-based dyes, such as N719, achieve PCEs of 18–22% under indoor lighting, while metal-free organic dyes offer a more cost-effective alternative with slightly lower efficiencies. The liquid electrolyte in traditional DSSCs poses leakage risks, but solid-state and quasi-solid-state variants have been developed to enhance durability. Long-term stability remains a focus, with recent designs showing less than 10% performance degradation after 10,000 hours of operation.

Efficiency under low-light conditions is a critical metric for indoor energy harvesters. Unlike outdoor solar cells, where high light intensity minimizes resistive losses, indoor devices must maximize charge extraction at low photocurrent densities. Key strategies include optimizing the active layer thickness to balance absorption and charge transport, reducing interfacial recombination, and minimizing series resistance. For OPVs, bulk heterojunction morphologies with bicontinuous donor-acceptor networks enhance exciton dissociation. Perovskite cells benefit from defect passivation and graded band alignment at the charge transport layers. DSSCs rely on redox mediators with fast regeneration kinetics to minimize losses at the dye-electrolyte interface.

Stability is another major consideration, as indoor photovoltaics must operate for years without significant degradation. Encapsulation is essential to prevent moisture and oxygen ingress, particularly for perovskites and OPVs. Barrier films with water vapor transmission rates below 10−6 g/m²/day are commonly employed. Thermal management is also crucial, as prolonged exposure to indoor lighting can raise device temperatures by 10–20°C, accelerating degradation mechanisms. For DSSCs, replacing volatile electrolytes with ionic liquids or polymers improves thermal stability.

Integration into smart home systems requires compatibility with low-power electronics and energy storage solutions. Indoor photovoltaics typically generate power densities of 10–100 µW/cm² under ambient lighting, sufficient for sensors, microcontrollers, and wireless communication modules. Energy management circuits, such as DC-DC converters and maximum power point tracking (MPPT) algorithms, are used to match the load requirements. Thin-film and flexible designs enable seamless incorporation into walls, furniture, and wearable devices. For example, OPVs can be printed onto curtains or wallpaper, while perovskite modules are laminated onto smart windows for dual-functionality as light harvesters and semi-transparent displays.

Material choices also influence environmental and manufacturing considerations. OPVs and DSSCs use solution-processable materials, reducing production costs and enabling roll-to-roll fabrication. Perovskites offer high efficiency but require careful handling of lead-based compounds. Research into lead-free perovskites, such as tin-based variants, addresses toxicity concerns but currently lags in performance. Scalability and reproducibility are ongoing challenges, particularly for perovskite deposition techniques like spin-coating, which are difficult to industrialize.

Future developments in indoor light harvesting will focus on improving efficiency-stability trade-offs and expanding application scenarios. Multi-junction designs, which stack materials with complementary absorption spectra, could push PCEs beyond 35% under indoor light. Machine learning-assisted material discovery may accelerate the optimization of organic and perovskite compositions for specific lighting conditions. Integration with energy storage, such as thin-film batteries or supercapacitors, will enable autonomous operation of IoT devices without grid dependence.

In summary, OPVs, perovskites, and DSSCs each offer distinct pathways for efficient indoor light harvesting. While OPVs excel in flexibility and tunability, perovskites lead in efficiency, and DSSCs provide robust performance under diffuse light. Advances in material design, encapsulation, and system integration will drive the adoption of these technologies in smart homes and beyond, enabling self-powered electronics that operate seamlessly under ambient lighting conditions.