Atomic Layer Deposition (ALD) to enable novel, high efficiency silicon nanorod solar cells
Due to the micrometer/sub-micrometer dimensions of the nanorod forests (dense packing, rod diameters typically few hundreds of nm and lengths < 1 μm) ALD has proven to be ideal technique for manufacturing some of the most crucial cell components. To prevent recombination losses in the active photovoltaic layer and thus cell efficiency decrease, a recombination barrier i.e. passivation layer needs to be coated on the rods’ surface. An ultrathin ALD-deposited Al2O3 film serves ideally this purpose, and the gas-phase, surface-controlled and self-limiting nature of the ALD process ensures that even the deepest and narrowest between-the-rods nooks and crannies will be reliably covered with 100 % uniform, conformal and pinhole- and defect-free passivation film. Another central cell component where ALD has shown its indispensability is the transparent conductive oxide (TCO) layer that works as the current collector on the top of the cell. Different TCO deposition methods were investigated in the course of the project, and ALD turned out to be the ideal method regarding both the TCO film quality and the scalability of the technique, due to Picosun’s fast, efficient and easy-to-use HVM (High Volume Manufacturing) batch ALD system, which was developed specifically during the project ROD-SOL.
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