DESIGN, FABRICATION AND CHARACTERIZATION OF INTERDIGITATED BACK CONTACT SOLAR CELLS

2022-4-22
Ciftpinar, Emine Hande
The design and development of high-efficiency interdigitated back contact (IBC) solar cells have been studied within the scope of this thesis. Developing a totally industry-compatible, lithography-free, high-throughput process flow for IBC cell fabrication was the main motivation of the thesis. For this, a detailed simulation study was conducted using Quokka 2 software to optimize the rear side cell geometry and understand the effect of bulk and layer properties on the device performance. After determining three different cell geometries with varying pitch values of 750, 1250, and 1700 µm, a totally screen-printing-based process flow was designed and applied to fabricate IBC cells. For selective diffusion, thick SiNx layers with optimized layer compositions were used as the diffusion barriers during the high-temperature boron and phosphorus diffusion process. The patterning of the barrier layers was done using a screen-printable ink with enhanced chemical resistance in acidic solutions. Following the optimization of the diffusion barrier properties and corresponding patterning step, diffusion and corresponding passivation properties were optimized. BCl3 and POCl3 diffusion recipes were studied in detail not only for the rear emitter and back surface field (BSF) regions but also for the front non-contacted junctions. Industrial fire-through (FT) metals pastes were used for the metallization of rear junctions whose corresponding optimization was done with the help of detailed contact resistivity analysis. Combining all optimized process parameters for the cell fabrication resulted in best cell parameters as FF:71.2%, Voc:642 mV, Jsc:37 mA/cm2 for FFE-IBC cell structure which were FF:70.3%, Voc:637 mV, Jsc:39 mA/cm2 for FSF-IBC structure. In addition to IBC studies, polySi passivating contact cells were also focused on in this thesis. In addition to their passivating properties, ex-situ doped polySi layers of varying thicknesses were studied also for their contacting properties. Excellent passivation properties were obtained for the case of n-polySi layers with the corresponding total recombination parameters (J0) of 1.6 and 7.4 fA/cm2 on textured and polished wafers, respectively. For the case of p-polySi layers, 16.3 and 70.2 fA/cm2 were obtained on the polished and textured wafers. Regarding the contacting properties, a novel methodology to extract the contact recombination parameter (J0,contact) was developed. The extracted J0,contact values were lying within the range of 300-400 fA/cm2 for relatively thicker n-polySi and p-polySi layers which increased to 1000 and 700 fA/cm2 for their thinner counterparts. Obtained J0,contact values were then correlated to high-resolution SEM images to better understand the contact formation and paste-polySi interaction.

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Citation Formats
E. H. Ciftpinar, “DESIGN, FABRICATION AND CHARACTERIZATION OF INTERDIGITATED BACK CONTACT SOLAR CELLS,” Ph.D. - Doctoral Program, Middle East Technical University, 2022.