Hydrogenation in multicrystalline silicon: The impact of dielectric film properties and firing conditions

Abstract

Hydrogenation is a crucial step for improving the efficiency of multicrystalline silicon solar cells. In this work, we investigate the influence of different firing and annealing conditions on the efficacy of bulk hydrogenation in state-of-the-art high-performance multicrystalline silicon, for a range of hydrogen-containing dielectric layers. All of the dielectric films studied, including aluminium oxide, amorphous silicon, and silicon nitride deposited with different tools, yield similar bulk lifetimes when annealed at optimal conditions. However, the optimal conditions vary between films, depending on the film properties. The overall hydrogenation effect does not appear to be affected by the cooling rate used during firing or by the application of illuminated annealing, performed at 250°C under 8 sun illumination.Moreover, we monitor in situ changes in the recombination behaviour of grain boundaries during the hydrogenation process, using a micro-photoluminescence spectroscopy system with a temperature controlled stage. It is found that the hydrogenation reaction occurs at the annealing temperature range between 400°C and 500°C.

Fluorine Passivation of Defects and Interfaces in Crystalline Silicon

“…Most of the GBs, appearing as dark lines in the PL images, were recombination active directly after phosphorus diffusion, consistent with previous work . The GBs remained recombination active in the samples annealed without any coating or with MgO.…”

“…Most of the GBs, appearing as dark lines in the PL images, were recombination active directly after phosphorus diffusion, consistent with previous work. 5 The GBs remained recombination active in the samples annealed without any coating or with MgO. In contrast, annealing the samples coated with LiF and MgF 2 resulted in the deactivation of GBs, with a similar degree of passivation as the hydrogenated SiN x -coated samples.…”

“…GBs are a type of extended crystal defect in mc-Si that are known to be strongly recombination active after high-temperature thermal processes such as diffusions but become largely inactive after a hydrogenation treatment. 5 This distinct behavior is utilized here to test our proposed fluorine incorporation method and demonstrate the passivation ability of fluorine.…”

“…Hydrogen is widely used in solar cell fabrication to saturate dangling bonds introduced by defects and impurities, passivating their electronic behaviors. Although hydrogen passivation is well known for improving interfaces − and some bulk defects, − hydrogen does not always provide complete passivation and is rather ineffective on certain defects such as dislocation clusters in cast-grown silicon . Furthermore, hydrogen itself in certain forms can also be recombination active in silicon. , …”

Electronic Properties and Structure of Boron–Hydrogen Complexes in Crystalline Silicon

“…[1,2] It has been found that hydrogen enhances the mitigation or deactivation of boron-oxygen defects responsible for the light-induced degradation in Czochralski-grown (Cz) Si solar cells and can passivate detrimental transition metal impurities, dislocation clusters, and thermally induced defects. [1][2][3][4][5] On the contrary, it has been suggested that hydrogen is responsible for the so-called light and elevated temperature-induced degradation (LeTID), which can produce a degradation of efficiency of solar cells between 2.5% and 16% relative and is most significant in multicrystalline Si passivated emitter and rear cells (PERC). [6][7][8][9] In most of the technologically important cases, the details of interaction of hydrogen atoms with other lattice defects are not well understood.…”