Hydrogen concentration at a-Si:H/c-Si heterointerfaces—The impact of deposition temperature on passivation performance

Abstract

We studied the effect of deposition temperature on the hydrogen distribution and the passivation performance of hydrogenated amorphous silicon (a-Si:H) coated crystalline silicon (c-Si) heterojunctions as a model of high efficiency solar cell structures. Nuclear reaction analysis (NRA) was employed to obtain hydrogen depth profiles of the heterojunctions prepared at temperatures from 80 to 180 °C. The implied open circuit voltage (i-VOC) and carrier lifetime monotonically increased with increasing deposition temperature in the as-deposited samples. NRA clarified that the hydrogen concentration (CH) at the a-Si:H/c-Si interface and in the a-Si:H layer decreased with deposition temperature. The hydrogen concentration around the interface was roughly 3 × 1021 cm-3 for the sample deposited at 180 °C. The NRA results are supplemented by optical constants obtained with spectroscopic ellipsometry (SE). At higher growth temperature, larger refractive indices and extinction coefficients were confirmed by SE analysis, suggesting that fewer hydrogen atoms are incorporated into the a-Si:H layers prepared at higher growth temperature. Furthermore, the passivation performance was enhanced by post deposition annealing (PDA) at 200 °C for 30 min. No significant change of the hydrogen distribution and optical constants was observed after PDA, suggesting that improved passivation is due to a local rearrangement of hydrogen at the molecular level that results in enhanced hydrogenation of dangling bonds.

Optimum Hydrogen Injection in Phosphorus-Doped Polysilicon Passivating Contacts

“…The negative impact of excess hydrogen on surface passivation observed in this work agrees with the literature. , Hollemann et al . performed firing experiments on n-type poly-Si/SiO x passivated lifetime samples with AlO x and SiN x stacks by varying the AlO x thickness and the peak firing temperature and compared the interface defect density ( D it ) calculated by the MarcoPOLO model and the hydrogen concentration measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS).…”

“…The negative impact of excess hydrogen on surface passivation observed in this work agrees with the literature. 44,45 Hollemann et al 44 performed firing experiments on n-type poly-Si/SiO x passivated lifetime samples with AlO x and SiN x stacks by varying the AlO x thickness and the peak firing temperature and compared the interface defect density (D it ) calculated by the MarcoPOLO model and the hydrogen concentration measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS). It was observed that a hightemperature firing at 863 °C can lead to excessive hydrogenation, in which the hydrogen concentration was several times higher than the corresponding D it , 44 implying the presence of hydrogen-related defects.…”

“…It was observed that a hightemperature firing at 863 °C can lead to excessive hydrogenation, in which the hydrogen concentration was several times higher than the corresponding D it , 44 implying the presence of hydrogen-related defects. In addition, Gotoh et al 45 studied the influence of the deposition temperature on the passivation performance and the hydrogen concentration in a-Si:H/c-Si heterojunctions with hydrogen depth profiling by nuclear reaction analysis. They found that the passivation performance can decrease with an increasing hydrogen level at the a-Si:H/c-Si interface.…”

“…They found that the passivation performance can decrease with an increasing hydrogen level at the a-Si:H/c-Si interface. 45 In the literature, while hydrogenation has been proven to be effective in improving the performance of solar cells, 34,46−48 hydrogen has been shown to cause recombination in multiple ways, such as formation of structural defects or platelets, 49,50 deactivation of phosphorus dopants, 51 formation of powerful recombination centers composed of carbon, oxygen, and hydrogen, 51,52 and creation of vacancy-hydrogen complexes. 53 It was also suggested that hydrogen itself could cause recombination, potentially resulting in a reduction in the carrier lifetime, 54 which might also be a possible explanation for the impact of excess hydrogen observed herein.…”

Hydrogenation Mechanisms of Poly‐Si/SiOx Passivating Contacts by Different Capping Layers

“…Compared to the as‐diffused sample, after the SiN x :H + FGA hydrogenation, the sample with pre‐FGA only showed a clear monohydride Si—H 1 peak, whereas the sample with pre‐AlO x :H + FGA displayed both monohydride Si—H 1 and dihydride Si—H 2 peaks, consistent with the literature . The presence of a dihydride Si—H 2 mode indicates that more hydrogen was injected into the films and incorporated with a larger amount of a‐Si phase . This result further agrees with the captured PL spectra from SiN x :H + FGA hydrogenated samples, as displayed in Figure C.…”