Desarrollo y caracterización de dispositivos fotovoltaicos p-i-n de silicio amorfo depositados por PECVD

Resumen

The present work approached the most relevant aspects in the development process of solar cells and modules based on amorphous silicon (a-Si:H) thin films. Since semiconductor characteristics determine the photovoltaic device performance, the first stage of this research was focused on the search for the correlation between deposition conditions and the optoelectronic properties of a-Si:H and a-SiC:H alloys (see chapter 3). The study allowed the finding of the conditions for the obtainment of good quality a-Si:H/a-SiC:H at low temperatures, compatible with the use of low-cost flexible substrates. After this step, the effort was reoriented to the preparation and characterisation of a-Si:H p-i-n solar cells. The fabrication process of these devices was optimised for the particular case of a dual-chamber PECVD. The design of the a-Si:H p-i-n structure was progressively improved at different deposition temperatures based on a detailed analysis of the optoelectronic behaviour of the resulting solar cell (see section 4.1). For this purpose, the standard techniques for device characterisation were complemented with a new I-V curve measurement setup that uses LEDs as source of monochromatic light of variable intensity (see section 2.3.4). The result of this evolution was solar cells with efficiencies close to state-of-the-art, which showed good homogeneity and reproducibility. Once enough technological maturity was reached, the work was focused on the implementation of some of the concepts that make a-Si:H technology of interest to the photovoltaic industry. Specifically, different tests of monolithic interconnection of solar cells were carried out, which allowed the fabrication of the first a-Si:H modules entirely developed with Spanish technology (see section 4.1.4). Subsequently, the work addressed the issue of cost reduction by means of substrates based on lower-price materials. Firstly, the effect on the device performance of the TCO material used as front electrode was analysed on glass substrates (see section 4.2). The study made a comparative between different TCOs, focusing on the particular case of AZO and the problem of the fill factor loss. Secondly, the research approached the fabrication of flexible solar cells by using PET substrates, paying special attention to the solution of peel-off problem (see section 4.3). The work concluded with the obtainment of the first fully operative flexible devices developed in CIEMAT.