We report on the latest progress in the field of organic p-i-n tandem solar cells. The external quantum efficiencies of a tandem solar cell with two complementary absorbing bulk heterojunctions with an efficiency of 6.07% (certified by Fraunhofer ISE) with an active area of about 2cm² is analyzed. These solar cells are extremely stable: a reduction of only 3% of its initial power conversion efficiency was measured when stored at 85°C for 5000 hours. The solar cell does not show any reduction in efficiency when stored under continuous illumination of a tungsten lamp corresponding to 1.5 suns for 5000 hours. Furthermore, we present the latest results on optimized tandem solar cells showing a power conversion efficiency of 7.66 % (certified by Fraunhofer ISE, active area of 1.1cm²).