SILICON SURFACE TREATMENT WITH SULFONIC ACID-BASED MATERIALS ENABLE SURFACE PASSIVATION AND SELECTIVE CHARGE TRANSPORT

Date

2023-6-22

Author

GHASEMIKASHTIBAN, MILAD

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One of the most pivotal factors in silicon photovoltaic (PV) for enhancing passivation quality of crystalline silicon is the reduction of surface recombination. Presently, dielectric materials with high passivation qualities are typically deposited under vacuum conditions and subjected to high-temperature annealing techniques. In the context of this investigation, we propose the utilization of two innovative materials, namely Heptadecafluorooctane sulfonic acid (HD) and Nonafluorobutane sulfonic acid (Nona). A notable advantage of these suggested materials lies in their ease of deposition and presence of hydrogen, oxygen, and fluorine in their molecular structure. The prescribed materials were applied to the surface of silicon utilizing the room-temperature spin-coating technique, with and without subsequent annealing procedures. The presence of the head group (SO3H), tail group (CF3), and linker (C F) within the molecular structure of these organic materials led to the observation of a self-assembled monolayer characteristic, as confirmed by contact angle measurements. The conformation of the self-assembled monolayer provides valuable insights into the orientation and arrangement of molecules on the silicon surface, elucidating the underlying passivation mechanisms. By coating these organic super vi acids (SA) onto Czochralski (Cz) crystalline silicon (c-Si) wafers characterized by base resistivity within the range of 1.5 to 2.5 Ω.cm, we achieved high implied Voc values (>740 mV) and an effective lifetime exceeding 8.5 ms. Moreover, the upper limit of surface recombination velocity (SRV) for the super acids was approximately 1 cm/s. A comparative analysis between the super acids and other dielectric passivating materials demonstrates the considerable potential of organic super acids in reducing surface recombination. Notably, both HD and Nona acids yielded contact resistivity values below 20 mΩ.cm-2 when applied between the silicon substrate and the aluminum electrode. Incorporating these super acids as electron-selective layers within the cell structure resulted in superior performance when compared to reference cells lacking SA interlayers. In the case of full-area rear contact cells, the utilization of HD and Nona superacid layers has yielded the highest achieved efficiencies of 17.08% and 17.09%, respectively. In contrast, the reference cell without the super acid layer demonstrated an efficiency of approximately 13%. This disparity in performance indicates a notable enhancement in cell efficiency resulting from the presence of HD and Nona super acids. Moreover, in the context of partial rear contact cells, the efficiencies exceeded 18% as a consequence of notable improvements in the fill factor (FF) and current density when compared to cells lacking the super acid layer. These improvements have led to an enhancement in cell efficiency of up to 1.5%, representing the most favorable outcome observed.

Subject Keywords

Surface passivation, Organic materials, lifetime, contact resistivity

URI

https://hdl.handle.net/11511/104528

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Graduate School of Natural and Applied Sciences, Thesis