Potential of amorphous and microcrystalline silicon solar cells

Low pressure chemical vapour deposition (LP-CVD) ZnO as front transparent conductive oxide (TCO), developed at IMT, has excellent light-trapping properties for a-Si:H p-i-n single-junction and ‘micromorph’ (amorphous/microcrystalline silicon) tandem solar cells. A stabilized record efficiency of 9.47% has independently been confirmed by NREL for an amorphous silicon single-junction p-i-n cell (~1 cm²) deposited on LP-CVD ZnO coated glass. Micromorph tandem cells with an initial efficiency of 12.3% show after light-soaking a stable performance of 10.8%. The monolithic series connection by laser-scribing for module fabrication has been developed at IMT as well, for both amorphous single-junction and micromorph tandem cells in combination with the LP-CVD ZnO technique. Mini-modules (areas between 22 and 24 cm²) with an aperture efficiency of 8.7% in the case of amorphous single-junction p-i-n cells (independently confirmed by NREL), and of 9.8% in the case of micromorph tandem cells, have been obtained. Micromorph tandem cells with an intermediate TCO reflector between the amorphous top and the microcrystalline bottom cell show an almost stable performance (η=10.7%) with respect to light-soaking.