Micromorph n-i-p tandem cells with asymmetric intermediate reflectors

We present tandem thin film silicon solar cells in n-i-p configuration with 12% initial efficiency. The stabilized efficiency of these devices is 10%. The result has become possible by the combination of a microcrystalline bottom cell with high current density and an asymmetric intermediate reflector that establishes a well adapted surface texture for the amorphous top cell. After successfully integrating these two steps, we obtain micromorph tandems cells with size of typically 0.25 cm2. The best cell among an array of 16 devices on the 4x4 cm2 sample area showed and initial efficiency of 12% with an open circuit voltage of Voc = 1.335 V, a short circuit current density of jsc = 12.1 mA/cm2 and a fill factor of FF = 74.2%. After carrying out the 1000 h light soak, this particular cell stabilized at 1.320 V, 11.9 mA/cm2, 62.7%, giving a stable efficiency of 9.8%. We observed some variation in the stabilized FFs, an adjacent cell with FF of 65.7 yields a stable efficiency of 10.0%