Despite recent significant breakthroughs yielding power conversion efficiencies (PCEs) that exceed 10%, the complicated multilayer structure of tandem polymer solar cells hinders their commercial manufacture via printing techniques. Current tandem architectures require a multilayered recombination center in combination with two or more p-type/n-type interfacial layers serially connecting two sub-cells, which increase the complexity of the fabrication process. Here, we demonstrate a new tandem architecture for printable photovoltaics using a versatile organic nanocomposite containing photoactive and interfacial materials. This nanocomposite forms an ideal self-organized recombination layer via a spontaneous vertical phase separation, which yields the simplest tandem structure fabricated to date with only four component layers. Moreover, our new tandem architecture exhibits a high tandem-PCE of 10.8%. Because our tandem architecture can be used with various organic photoactive materials, our new approach offers a universal method for producing cost-effective printable electronics.