Static Large-Area Hydrogenation of Polycrystalline Silicon Thin-Film Solar Cells on Glass Using a Linear Microwave Plasma Source

Hydrogenation of polycrystalline silicon thin-film solar cells on glass is performed to improve the open-circuit voltage V_oc of the devices. The hydrogenation process is performed using linear microwave plasma sources that are capable of generating a uniform hydrogen-argon plasma over a large area. The substrate is fixed (i.e., does not move) during the hydrogenation process. The optical emission intensities from the hydrogen-argon plasma are recorded at two wavelengths using an optical emission spectroscopy system and are used to study the impact of several process parameters. The impact of these process parameters on the device´s V_oc is also studied. We demonstrate that this plasma reactor is able to hydrogenate samples with a size of up to 400 cm². The uniformity of the hydrogenation process is evaluated by measuring the 1-sun V_oc with a suns-V_oc tester, giving voltage variations of less than ±3%. The highest average V_oc achieved in this study is 465 mV on a 10 cm × 10 cm textured sample and 428 mV on a 20 cm × 20 cm textured sample. In addition, secondary ion mass spectroscopy is used to measure the hydrogen concentration in the poly-Si films, giving an average concentration of about 6 × 10¹⁹ cm^-3.