We first introduce a new electrode structure for organic solar cells (OSCs), the so-called interdigitated horizontal electrode (IHE), in which an electron-collecting electrode and a hole-collecting electrode are horizontally separated. In the IHE, the directions of the incident light and the charge collection are perpendicular to each other. Therefore, the thickness of the photoactive layer is no longer limited by the poor electrical mobility of the carriers in the organic-based photoactive layer. An analysis of the electrical, optical, and electrochemical properties of the IHE is presented. For poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C60 butyric acid methyl ester (PC60BM)-based IHE OSCs, a proof-of-principle demonstration is performed of their feasibility as electrodes. Such OSCs yielded a power-conversion efficiency of 1.2 ± 0.1%, with a short-circuit current density (JSC) of 13.6 ± 0.2 mA/cm2, which is larger than the JSC of 8.5 ± 0.2 mA/cm2 of the reference OSCs with their conventional stacked structure.