ETL-free and HTL-free perovskite solar cell as the simplified power source for energy-frugal indoor IoTs

• Simplified Architecture: Researchers developed a "fully stripped-down" solar cell by removing the Electron Transport Layer (ETL) and Hole Transport Layer (HTL), significantly reducing manufacturing complexity and cost. • Chemical Enhancement: By introducing EMIM Ac into the perovskite layer, they improved energy alignment and crystallinity to overcome the efficiency losses usually found in simpler cell designs. • Practical Application: The resulting cell achieved an efficiency of 12.53% under indoor lighting, proving it is a viable, low-cost power source for energy-frugal Internet of Things (IoT) devices. Perovskite solar cells (PSCs) offer a promising pathway towards low-cost, high-efficiency photovoltaics. However, conventional PSCs require at least two charge transport layers (ETL and HTL), increasing fabrication complexity and cost. ETL-free PSCs present a cost-effective alternative but suffer from energy-level misalignment at the perovskite/electrode interface, leading to charge recombination and efficiency losses. Recent studies have employed interfacial modifications to improve energy alignment, yet these still retain multilayer structures. In this work, we developed a simplified, fully ETL- and HTL-free PSC architecture (FTO/Cs 0.1 (FA 0.88 MA 0.12 )Pb(I 0.7 Br 0.3 )(CsFAMA 1.7 eV)/Phenethyl ammonium iodide (PEAI)/Carbon) via introducing 1-ethyl-3-methylimidazolium acetate (EMIM Ac) into the perovskite layer, causing better energy level alignment, reduced trap density, and improved crystallinity. The fully striped-down structure surprisingly achieves an efficiency of 12.53% under 1,000 lux, sufficient to be a battery replacement for indoor energy frugal IoTs, while lowering production costs by minimizing layers and processing steps. Our findings highlight ultra-lean PSCs, which comprise of only perovskite and two electrodes, demonstrating the simplified solar cell structure to date, which is fully capable of powering indoor IoT applications.