Organic photovoltaics (OPVs) offer a promising solution for indoor energy harvesting. However, fundamental investigations to understand and optimize industrial processes such as roll-to-roll lamination for upscaling remain limited. This study investigates a critical failure mode in the upscaling of OPVs. One major challenge for thick semitransparent laminated OPV devices is current-voltage (J-V) asymmetry, where performance under cathode-side illumination exceeds that under anode-side illumination. X-ray reflectivity, neutron reflectivity, and drift-diffusion simulations reveal that a vertically stratified polymer-rich region within the bulk of photoactive layers is the main cause of asymmetric J-V characteristics. Based on this fundamental understanding, a model is proposed to explain the mechanism, wherein electron extraction is hindered by the polymer-rich region during anode illumination. By exploring upscaling-compatible blends, cathode/anode-balanced, high-performing, and air-stable semitransparent laminated OPVs are developed for indoor applications using commercially available PV-X-plus material. These findings provide valuable guidance for designing OPVs with balanced performance, facilitating roll-to-roll adoption and commercialization.