Fully blade coated carbon-based HTL-free perovskite solar cells and modules processed under ambient conditions for efficient indoor photovoltaics

Carbon electrode-based perovskite solar cells (cPSCs) offer a compelling route toward scalable, simplified photovoltaics. Conventional architectures, however, rely on organic hole transport layers (HTLs) that increase fabrication cost and compromise long-term stability. HTL-free cPSCs (HcPSCs) address both limitations by combining simplified device stacks with improved durability, where the perovskite/carbon interface governs performance, making defect passivation and recombination suppression at this junction critical design priorities. Here, we investigate the performance of HcPSCs under indoor illumination of 200 lx, 500 lx, and 1000 lx. Using a commonly used octyl ammonium iodide (OAI) based post-treatment at the perovskite/carbon interface, a 70% improvement in indoor power conversion efficiency (iPCE) was achieved, delivering one of the highest efficiency of 29.34% under 1000 lx white LED illumination (3000 K) for devices with an active area of 0.92 cm2. Long-term shelf-life stability, assessed under 1000 lx illuminance, reveals substantially enhanced longevity, with a t90 of more than 4000 h (1762 hours for the reference) for the post-treated HcPSC device stack. As a proof of concept, we further demonstrated the performance of post-treated HcPSC mini-modules (10.40 cm2 active area), achieving an iPCE of 15.34%, while retaining more than 90% of their initial performance after 800 h, during the shelf-life stability test under 1000 lx illumination. These results establish fully blade-coated, ambient-processed, HTL-free carbon perovskite solar cells as a promising scalable platform for efficient and stable indoor energy harvesting.