An efficient organic solar cell is fabricated by the weak-epitaxy-growth method and the achieved power conversion efficiency is over 3% (see figure). A Single-crystal-like thin film improves the carrier mobility and reduces the electron hole recombination. Deposition of a zinc phthalocyanine (ZnPc):C60 mixed layer at 100 degrees C results in a better interpenetrating interface and the device performance is improved.