An international research team has improved the performance of perovskite indoor photovoltaics by tuning the absorber bandgap to better match the emission spectrum of indoor LED lighting. The approach enables improved spectral alignment under low-light conditions, with devices demonstrating efficiencies of up to 37.44% alongside long-term stability exceeding 2,000 hours.
Device prototype
Image: King Abdulaziz City for Science and Technology (KACST)
An international research team claims to have improved the performance of perovskite indoor photovoltaics (PIPV) by tuning the bandgap of  the perovskite material for the typical operational conditions indoor LED lighting.
Tuning the perovskite bandgap is critical in this context, as it enables improved spectral matching with the narrow and lower-intensity emission spectrum of indoor LED lighting, thereby maximizing photon harvesting and device efficiency under low-light conditions.
“This study delivers a decisive shift in indoor photovoltaics by moving beyond conventional outdoor optimization paradigms and establishing a bandgap-by-design framework tailored specifically for indoor lighting,” said corresponding author Essa A. Alharbi to pv magazine. “Through precise compositional engineering of methylammonium-free CsₓFA₁₋ₓPb(I₁₋yBry)₃ perovskites, we directly link absorber bandgap to spectral matching under realistic white LED conditions (3,000–5,500 K, 250–1,000 lux).”
“The work goes beyond proof-of-concept devices by demonstrating high efficiencies in a scalable mesoscopic n–i–p architecture with an active area of 1 cm², alongside operational stability exceeding 2,000 hours under indoor illumination,” he added. “This combination of spectral optimization, scalability, and durability establishes a practical blueprint for next-generation PIPVs.”
Three devices were fabricated using a conventional mesoscopic n–i–p architecture. The structure consists of a fluorine-doped tin oxide (FTO) transparent conducting substrate, followed by compact titanium oxide (c-TiO₂) and mesoporous TiO₂ (m-TiO₂) electron transport layers. The perovskite absorber was deposited on top of the mesoporous scaffold, and a Spiro-OMeTAD layer was used as the hole transport material. The stack is completed with a thermally evaporated gold (Au) back contact.
In all devices, only the perovskite absorber composition was changed by adjusting the iodide-to-bromide (I/Br) ratio, which controls the bandgap and improves the match to indoor LED spectra. The first device used FA₀.90Cs₀.10Pb(I₀.98Br₀.02)₃, with only 2% bromide, giving a bandgap of 1.55 eV. The second used FA₀.85Cs₀.15Pb(I₀.55Br₀.45)₃, with 45% bromide, resulting in a 1.72 eV bandgap. The third used FA₀.85Cs₀.15Pb(I₀.15Br₀.85)₃, with 85% bromide, producing the widest bandgap of 1.88 eV.
Each of the three devices was measured under a range of light intensities and LED color temperatures: 1,000, 500, and 250 lux, and 3,000 K, 4,000 K, and 5,500 K, respectively. Performance was evaluated in terms of power conversion efficiency (PCE), open-circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF) using J–V measurements under all nine lighting conditions.
In addition, the devices were characterized using photoluminescence (PL) spectroscopy to confirm the bandgap, X-ray diffraction (XRD) to assess crystal structure and phase purity, scanning electron microscopy (SEM) and atomic force microscopy (AFM) to examine morphology and surface roughness, and long-term stability testing under indoor illumination for up to 2,000 hours.
“The most striking result is the emergence of the 1.72 eV composition as a universal performer, delivering consistently high efficiencies across a wide range of light intensities and color temperatures. Its reduced sensitivity to spectral variations challenges the conventional expectation that wider band gaps inherently lead to narrow operating windows,” said Alharbi. “Equally notable is the exceptional peak efficiency of 37.44% achieved by the 1.88 eV device under low-intensity (250 lux, 5500 K) illumination. Despite known recombination challenges in wide-bandgap systems, this result shows that near-perfect spectral alignment can outweigh intrinsic material limitations under specific indoor conditions.”
Most notably, the researcher said, the study reveals critical design insight. “There is no single ‘optimal’ bandgap for indoor photovoltaics. Instead, device performance is strongly illumination-dependent, exposing a key limitation in current PIPV design strategies and highlighting the need for adaptive or application-specific optimization,” he explained.
In conclusion, Alharbi said that the next phase of the study will target one of the main bottlenecks in high-bandgap perovskites: trap-assisted recombination. “Through defect passivation and interface engineering, we aim to unlock the full efficiency potential of >1.8 eV absorbers while preserving long-term stability under indoor conditions,” he said. “Importantly, the research will move from the lab to real-world deployment. We will integrate these devices into functional Internet of Things (IoT) systems, to validate continuous, maintenance-free operation under practical indoor conditions.”
The research work was published in “Bandgap engineering for efficient perovskite solar cells under multiple color temperature indoor lighting,” in Materials Advances. Scientists from Saudi Arabia’s King Abdulaziz City for Science and Technology (KACST), King Saud University, and Taibah University, as well as Greece’s Foundation for Research and Technology – Hellas (FORTH), Hellenic Mediterranean University (HMU), and University of Crete have participated in the study.
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