We herein advance the application of a two-dimensional (2D) photonic crystal (PC) as a window layer in an efficient polymer solar cell (PSC). The PSC used here consisted of a photovoltaic (PV) layer of poly(3-hexylthiophene): methanofullerene bulk-heterojunction with a planarized 2D PC window layer made of a hexagonal array of columns of SiO(2) nano-rods embedded in a dielectric layer of SiN(x). By means of a theoretical simulation of the 2D PCs using a finite-difference time-domain (FDTD) method, it was shown that the path length of the incident light can be increased with a large deflection angle. The experimental results confirmed the simulated results obtained using the 20 PC layer. Furthermore, it was shown that a relative increase in power conversion efficiency (PCE) of about 25% was achieved for the PSC with the 2D PC layer, indicating that this layer induces further photon absorption due to efficient light-harvesting within the PV layer. (C) 2010 Elsevier B.V. All rights reserved.