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The purpose of this thesis is to investigate an innovative and promising approach to increasing the efficiency of low-cost amorphous Si (a-Si:H) solar cells. In essence, the approach involves incorporating semiconducting nanoparticles (NP) in a-Si:H solar cells as absorbers, exploiting the high absorption coefficients of the nanoparticle sand the low production costs of the a-Si:H solar cells, which are grown at low temperature. Producing NPs in a first step, and then embedding them in the solar cell in a second step, offers new degrees of freedom to optimize the nanoparticle absorbers. Promising NP material systems were investigated with respect to their composition, morphology and structural defects, in order to find NPs suitable for embedding. The FeSi2 NPs investigated are the first pure beta-phase NPs reported so far. A range of posttreatment methods were found for optimizing them in order to meet the requirements for NP absorbers. Suitable NPs of alpha-Fe2O3, Cu2O, CuO and Cu31S16 were embedded in a-Si:H solar cells to study the influence of the plasma-enhanced chemical vapor decomposition (PECVD) growth process on the NP absorbers and vice versa. The a-Si:H solar cells based on-Fe2O3 NPs reach efficiencies of 1.3%. This shows that it is possible to embed NPs in aworking a-Si:H solar cell using PECVD. However, the alpha-Fe2O3 NP-based solar cell was not superior to a reference a-Si:H solar cell. An SiOx shell was observed at the interface between the NPs and the a-Si:H solar cell. This shell is attributed to a chemical reduction of the NPs during embedding. It reduces carrier extraction and the contribution of the NPs to the solar cell efficiency. Studies of the embedding of the Cu2O, CuO and Cu31S16 revealed that two different decomposition mechanisms take place during PECVD embedding: chemical reductionand diffusion of the NP elements. With the identification of these two decomposition mechanisms, it is now possible to select NPs that are stable during PECVD embedding. Such NP material systems are bothoxygen-free and composed of materials with low mobilities in a-Si:H. Therefore, optimized beta-FeSi2 NPs or FeS2 and ZrS2 NPs are promising absorbers for the development of future NP-based solar cells. |
