ALD layers have many useful insertion points for solar cells. Crystalline silicon solar cells show dramatic improvement in efficiency when passiviated with Al2O3. The ALD Al2O3layer repairs defects on the surface and therefore decreases losses due to recombination of the charge carriers in the silicon.1
For thin film solar cells based on copper-indium-gallium-diselenide (CIGS), ALD ZnS/ZnO has been shown to be a low-cost and Cd-free buffer layer.2,3 Tailoring the interfaces of the ZnOS and the buffer layer itself, can be accomplished by varying the ratio of oxygen to sulfur in the film or by adding in other dopant components, such as In2O3, In2S3, MgO or Ga2O3.4,5 ALD is optimal for controlling the ratio of ZnO to ZnS in the ZnOS buffer, which is required for controlling the bandgap matching to the CIGS compositon. Final encapsulation of the CIGS solar-cell with ALD film has shown to dramatically improve the operating lifetime of the solar cell.6
Low-cost photovoltaics, such as those based on polymers, or dye-sensitized solar cells can employ ALD in the device stack as the TCO (transparent-conducting oxide), the photo-anode,7 for fabrication of the electrode, or as an interfacial layer / charge-recombination barrier.8-10 Novel electrodes can be fabricated by coating the inside of porous structures, such as nanotubes or AAO with ZnO or TiO2.11 New approaches, such as Plasmon based DSSCs, continued to be investigated and are enabled through the use of ALD TiO2 and Al2O3.12 After fabrication of an organic PV cell, encapsulation with ALD films are particularly important to prevent damage from exposure to atmosphere.13,14
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