<p>The operational stability of perovskite solar modules (PSMs) is inferior to that of smaller-sized devices, posing a critical challenge to advance their practical applications. Printable carbon electrodes are highly stable and cost-effective, representing a promising strategy to address the stability issue when used as rear contacts in fully printable PSMs. However, the power conversion efficiency (PCE) of carbon-electrode PSMs still lags behind their metal-electrode counterparts. Here we develop a scalable vapour post-treatment process based on molecules with small sizes and low boiling point that effectively minimize non-radiative recombination and facilitate charge extraction. We demonstrate fully printed carbon-electrode PSMs with about 50 cm² of active area and a PCE of 20.41% (19.26% certified). Our strategy significantly improves the stability of modules, with negligible PCE decay after tracking at the maximum power point for 1,020 h under 1-sun illumination at 65 °C. The unencapsulated carbon-electrode PSMs retain over 84% of the initial PCE under the damp heat test (85 °C and 85% relative humidity) for 2,280 h. We believe our treatment strategy will sustain the development of carbon-electrode PSMs towards commercial upscaling.</p>