This work focuses mainly on development of modulated surface texturing of Al substrate for thin-film, silicon-based, flexible solar cells. We compared the current roll-to-roll process at industrial level with a newly developed lab-scale texturing that offers better performance both with KOH and NaOH etching of Al foil. The kinetics of these etching chemicals, modelled with an Arrhenius equation, is evaluated in both methods, activation energy and pre-exponential factor are calculated depending on etching concentration. We also deployed a new roll-to-roll experiment that shows better optical properties than the baseline. Finally, we also show the first results of micromorph tandem devices on the baseline texturing.

In this work we focus on texturing Al substrate in order to employ the modulated surface texturing approach for thin-film, flexible, micromorph solar cells. We deployed two different methods to induce micro-craters in Al foil, i) bare Al etching by KOH and ii) AZO sacrificial layer etched in KOH. After modelling the etching kinetics of KOH on Al, we characterized the 2D correlation length and rms roughness of these samples and find the optimal aspect ratio of 12% to deposit high-quality 3 µm-thick nc-Si. Finally, excellent angular scattering properties have been measured for both employed methods.

Thin-film silicon single- and multi-junctions are a viable option to manufacture lightweight, flexible solar modules via high-throughput roll-to-roll (R2R) processes, starting from earth-abundant, non-toxic raw materials, at very cost competitive levels and with a range of application spanning from large area solar plants to portable devices. Nevertheless, flexible thin-film silicon modules have currently lower power conversion efficiency (PCE) compared to modules fabricated on glass substrates. Here, we focus on improving the efficiency of flexible single-junction modules by changing the chemical composition and the growth conditions of the p-doped window layer. Highly efficient devices require a window layer with excellent optical and electronic properties so that incoming light photons can easily reach the absorber layer, while photogenerated holes can be promptly extracted from the device. Our baseline modules have a p-doped hydrogenated silicon carbide (p-SiC:H) window layer. In order to simultaneously reduce optical losses and improve the charge collection, we reduced the thickness of p-SiC:H by modifying the plasma enhanced chemical vapor deposition tool, and we inserted a layer of p-doped nanocrystalline silicon oxide (p-nc-SiOx:H) in between p-SiC:H and TCO. The double p-layer modules that we obtained showed a 2% increase in the open circuit voltage compared to the single p-layer modules. Fine-tuning the deposition conditions for both p-layers will further reduce optical and resistive losses and improve the PCE of the modules; additionally, the double p-layer architecture will allow for an accurate control of the light transmission through the window layer, facilitating the current matching for multi-junction modules.