The authors report on the fabrication of microcrystalline silicon p-i-n solar cells with efficiencies close to 10%, using glass coated with zinc oxide (ZnO) deposited by low pressure chemical vapor deposition (LPCVD).LPCVD front contacts were optimized for p-i-n microcrystalline silicon solar cells by decreasing the free carrier absorption of the layers and increasing the surface roughness. These modifications resulted in an increased current density of the solar cell but also in significantly reduced fillfactor (FF) and open-circuit voltage (Voc). In order to avoid these reductions, a new surface treatment of the ZnO is introduced. It transforms profoundly the surface morphology by turning the typical V-shaped valleys of the LPCVD ZnO into U-shaped valleys and by erasing from the surface small-sized pyramids and asperities. As a result, for fixed deposition parameters, the p-i-n microcrystalline silicon solar cell efficiency increased from 3.3% to 9.2%Further optimization of the microcrystalline silicon solar cell on this 'new' type of LPCVD ZnO front contact has led to an efficiency of 9.9%.
Amorphous silicon p-i-n solar cells and modules have been developed in small R&D KAI reactors. Test cells of 0.25 mm thick i-layer exceed 10 % initial efficiencies and stabilized ones of 8.2 %. The a-Si:H deposition process is successfully transferred to industrial size substrates of 1.4 m 2 area resulting in initial module powers of 106.4 W using a commercial TCO front AFG and, recently, 104.1 W using in-house developed LPCVD front ZnO. For both modules our in-house LPCVD ZnO has been applied as back contact. The former large-area module passed successfully the damp-heat test. Entirely microcrystalline p-i-n cells with an efficiency of 8.5 % could be prepared in a single-chamber KAI-S reactor. Micromorph tandems resulted in initial cell efficiencies of 10.7 %, whereas minimodules lead to initial aperture efficiencies of 10.2 %.
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