Optimization of low cost processes for thin crystalline silicon solar cell production
- Autores: Efrain Ochoa Martinez
- Directores de la Tesis: José Ramón Ramos Barrado (dir. tes.), S. Palanco (codir. tes.)
- Lectura: En la Universidad de Málaga ( España ) en 2013
- Idioma: español
- Tribunal Calificador de la Tesis: Bernabé Marí Soucase (presid.), Mercedes Gabás Pérez (secret.), Jesus Alonso Reviejo (voc.), Bouchaib Hartiti (voc.), Marek Tlaczala (voc.)
- Materias:
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- Resumen
The current trend in the photovoltaic industry passes through increasing efficiency and reducing costs of the modules. Over 40% of these costs originate in the semiconductor substrate material; therefore the logical step is to reduce the thickness of the cells. However, due to the fragility of the substrate the manufacturing processes have to be optimized for the new conditions of the wafers, the aim is to implement in¿line techniques which increase productivity and contact¿less techniques to decrease the breakage yield.
The preparation of thin films by spray of liquid precursor is a low cost alternative for various processes in the manufacture of solar cells. The laser processing and subsequent plating of the front face contacts can also be considered a low cost alternative taking into account that it dispenses specialized and expensive materials and metallization pastes, besides being a very low contact technique, favoring the reduction of breakage.
Additionally, given that the high cost of silver is becoming one of the limiting factors for reducing the cell price, the implementation of copper plating allows a potential cost reduction.
This Thesis describes the results obtained in the development of in¿line spray coated phosphorus and boron emitters. A system for silicon doping through spraying of liquid precursors has been purposely designed and built. There have been produced phosphorus n¿type and boron p¿type emitters from commercial and self¿made precursor solutions, controlling the process to achieve the desired resistivities.
Regarding the improvement of the frontal metallization process, a seed and plating approach has been analyzed. The seed layer is deposited by laser chemical processing, depositing a nickel rich layer for subsequent copper plating. Conditions have been optimized for the case of textured crystalline cells in order to reduce the number of scan sweeps required, and consequently the processing time per cell. The finger widths obtained are below 40 ¿m, thus reducing the shaded area.
Chemical, electrical and morphological characterization results are presented before and after the formation of the emitter, and after completion of the device. The produced solar cells show viability of both processes, leading to solar cells up to 100 ¿m thick with a 12.2% efficiency in the case of spray coated thin cells featuring a traditional screen printing metallization, and 15.2% for the seed and plating cells.
