Hydrogenated microcrystalline silicon prepared at low temperatures by the glow discharge technique is examined here with respect to its role as a new thin-"lm photovoltaic absorber material. XRD and TEM characterisations reveal that microcrystalline silicon is a semiconductor with a very complex morphology. Microcrystalline p}i}n cells with open-circuit voltages of up to 560}580 mV could be prepared.`Micromorpha tandem solar cells show under outdoor conditions higher short-circuit currents due to the enhanced blue spectra of real sun light and therefore higher e$ciencies than under AM1.5 solar simulator conditions. Furthermore, a weak air mass dependence of the short-circuit current density could be observed for such micromorph tandem solar cells. By applying the monolithic series connection based on laser patterning a "rst micromorph mini-module (total area of 23.6 cm) with 9% cell conversion e$ciency could be fabricated.
Intrinsic microcrystalline silicon opens up new ways for silicon thin-film multi-junction solar cells, the most promising being the ''micromorph'' tandem concept. The microstructure of entirely microcrystalline p-i-n solar cells is investigated by transmission electron microscopy. By applying low pressure chemical vapor deposition ZnO as front TCO in p-i-n configurated micromorph tandems, a remarkable reduction of the microcrystalline bottom cell thickness is achieved. Micromorph tandem cells with high open circuit voltages of 1.413 V could be accomplished. A stabilized efficiency of around 11% is estimated for micromorph tandems consisting of 2 mm thick bottom cells. Applying the monolithic series connection, a micromorph module (23.3 cm 2 ) of 9.1% stabilized efficiency could be obtained.
Amorphous silicon p-i-n solar cells were deposited on "in house" developed LP-CVD zinc oxide and compared with commercially available SnOa (Asahi type U2) substrates.While for both front TCO materials comparably high values of the open circuit voltage (860-900 mV) and of the fill factor (72 -74 %) were obtained, a remarkable enhancement of the short-circuit current density could be observed for LP-CVD ZnO substrates. Optical characterizations confirm for LP-CVD ZnO a more efficient light-trapping effect, as compared to SnOa. By applying this low-cost LP-CVD ZnO, a stabilized a-Si:H p-i-n solar cell efficiency of 9 % has been achieved.
The well-established laser-scribing currently used for a-Si:H module fabrication, has been applied to "micromorph" (a-Si:H/µc-Si:H) tandem solar cells deposited on glass/ZnO substrates. Thereby, a laser at a wavelength of 1064 nm was used for scribing the ZnO and a laser with a wavelength of 532 nm for the silicon film scribing. It is shown that with glass-side scribing, both the 0.3 µm thick a-Si:H top cell as well the 3 µm µc-Si:H bottom cell can be patterned in one single pulse. Monolithic integrated series connection is obtained with a total of 3 patterning steps. These first experiments allowed for fabrication of micromorph mini-modules (area 23.3 cm 2 ) having 6 segments has been fabricated with a stable aperture efficiency of 9.1 % (Voc = 8.014 V, FF = 66.6 %, Isc = 39.72 mA).
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