Researchers from Taiwan's National Yang Ming Chiao Tung University and Flexwave have developed a self-adaptive interfacial nanostructure (SAIN) for the hole-extraction contacts of inverted perovskite solar cells, reporting a power conversion efficiency (PCE) approaching 20% under standard 1-sun illumination and 38.16% under indoor lighting at 2,000 lux - a figure that climbs above 40% once paired with an optical enhancement film, placing the device among the most efficient indoor perovskite solar cells reported to date.
The team explains that "regular" n-i-p configurations tend to reach higher efficiencies, but inverted PeSCs offer better long-term stability and are easier to stack into multijunction devices, making the p-i-n architecture an attractive target for further improvement. A major bottleneck in inverted PeSCs is the buried hole-transport layer (HTL) sitting beneath the perovskite film. Because the perovskite crystallizes directly on top of it, the HTL's quality shapes both the interface and the growing perovskite layer itself, and a poor HTL drives up non-radiative recombination - carriers lost to defects rather than converted into current, which shows up as low photoluminescence quantum yield in the finished film. Today's leading inverted devices typically grow their perovskite on either a hole-conducting polymer such as poly(triarylamine) (PTAA) or a self-assembled monolayer (SAM) built from carbazole-based molecules. Each has drawbacks: high-quality PTAA is costly to produce, while SAMs are difficult to deposit as a conformal, densely packed layer, which hurts device-to-device reproducibility. Both materials are also hydrophobic, complicating full-coverage perovskite deposition over large areas. Hybrid PTAA-plus-SAM contacts have been explored to combine their strengths, but so far only for standard 1-sun operation, leaving their potential for indoor photovoltaics untested.
Indoor photovoltaics are a particularly attractive niche for perovskites, since their bandgap can be tuned to match the emission spectrum of common indoor light sources, making PeSCs well suited to powering low-energy Internet of Things (IoT) devices and sensors - letting them run longer between battery changes.
The team's SAIN structure combines PTAA with the SAM molecule (3,6-Dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid, known as Me-4PACz. Fabrication starts with spin-coating a diluted PTAA solution onto the indium tin oxide (ITO) electrode, filling in the grain boundaries of the ITO surface, before Me-4PACz is applied on top. Rather than forming a fixed, static layer, the SAM molecules adopt an orientation that adapts to the underlying PTAA, producing a surface tuned to support high-quality perovskite growth above it. This self-adaptive arrangement aligns the energy levels across the contact and cuts down surface recombination, addressing the reproducibility and coverage problems that have limited PTAA- and SAM-only contacts.
Under standard 1-sun illumination, the SAIN-based device reached a PCE of close to 20%. Under indoor lighting, performance was markedly stronger: 33.54% at 200 lux and 38.16% at 2,000 lux. Adding an optical enhancement film on top pushed the indoor PCE past 40%, ranking the device among the best-performing indoor PeSCs reported so far. The devices also showed improved reproducibility compared with PTAA- or SAM-only contacts, a factor the researchers point to as encouraging for future large-scale production and commercialization of indoor perovskite photovoltaics.
