Kamjam N.Choodam K.Sukpan N.Kittikool T.Seriwattanachai C.Kamnoedmanee S.Hu Y.Supruangnet R.Nakajima H.Kaewprajak A.Kumnorkaew P.Wongratanaphisan D.Ruankham P.Pakawatpanurut P.Kanjanaboos P.Mahidol University2026-04-292026-04-292026-06-01Results in Engineering Vol.30 (2026)https://repository.li.mahidol.ac.th/handle/123456789/116360Perovskite solar cells (PSCs) offer a promising pathway toward 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<inf>0.1</inf>(FA<inf>0.88</inf>MA<inf>0.12</inf>)Pb(I<inf>0.7</inf><inf>0</inf>Br<inf>0.3</inf><inf>0</inf>)(CsFAMA1.7 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 1000 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, which is fully capable of powering indoor IoT applications.EngineeringArticleSCOPUS10.1016/j.rineng.2026.1103772-s2.0-10503612405525901230