Polymer solar cell (PSC) manufacturing is strongly influenced by the thin film deposition method with the morphology of the bulk heterojunction (BHJ) coupled intimately to the efficiency of the device. Although ideally scalable deposition methods suitable for sheet-to-sheet (S2S) or roll-to-roll (R2R) production should be used in the investigation of PSCs, research still predominately relies on spin-coating due to ease of use and lower associated costs. Here we present the development and characterization of a lab-scale slot-die coater and demonstrate its use to fabricate air-stable, large-area, solar cell modules. We adapt an entry level paint applicator into a fully-functional S2S slot-die coater and provide its open source documentation to support the research community in availing itself of scalable photovoltaic technologies for device fabrication. The optimization of the process parameters results in homogeneous layers that have been extensively characterized by light beam induced current (LBIC), micro photoluminescence (PL), and micro Raman mapping of whole modules. We report the successful demonstration of the fabrication of PSC modules with an active area above 35 cm(2) and a power conversion efficiency exceeding 3%. We also investigate the behavior of the module characteristics at different annealing temperatures and its stability during operation under ambient conditions. This work will facilitate research on scaling up of laboratory organic electronic devices and allow more efficient transition from Lab-to-Fab.