Correlation between in Situ Diagnostics of the Hydrogen Plasma and the Interface Passivation Quality of Hydrogen Plasma Post-Treated a-Si:H in Silicon Heterojunction Solar Cells

Abstract

Passivation of the interface defect states is crucial to mitigate the recombination losses in silicon solar cells. In this work, we have investigated the role of hydrogen plasma treatment (HPT) to passivate the interfacial defects between crystalline (c-Si) and hydrogenated amorphous silicon (a-Si:H) in silicon heterojunction (SHJ) solar cells. For the first time, we have found a correlation between the dynamic properties of hydrogen plasma and passivation quality of the films by using in situ optical emission spectroscopy and quasi-steady state photoconductance measurement. The optimum condition for saturation of the dangling bonds by HPT has been studied in detail by tuning the excited hydrogen (H) species and ion bombardment energies by controlling physical parameters like plasma current and chamber pressure. We have investigated the role of annealing after HPT to redistribute the H in the post-treated a-Si:H film and have obtained an iV oc of 755 mV, minority carrier lifetime (τ eff ) of 4.6 ms, and SRV of 1.5 cm/s on test structures having only an 10 nm intrinsic a-Si:H layer on textured silicon wafers. The H bond configuration at the interface of a-Si:H and c-Si has been investigated by Fourier transform infrared spectroscopy, which demonstrates improved monohydride bonding in the films after HPT derived from the analysis of microstructure parameter and H concentration values. Raman spectroscopy shows the absence of the nanocrystalline fraction after HPT and verifies reduced coordination defects due to annealing after HPT. The proof of concept has been validated by fabricated SHJ solar cells having a V oc of 729 mV and efficiency of 18.7% after HPT, with the best cell efficiency reaching 20.2% after doped layer optimization. The decrease in reverse saturation current and ideality factor after HPT verifies that the improvement in performance is from reduced recombination losses at the interface due to passivation of defects in midgap states.

Hydrogen Plasma Exposure of Monolayer MoS2 Field-Effect Transistors and Prevention of Desulfurization by Monolayer Graphene

“…The HPE was performed in a custom-built direct current plasma system. Incident protons with a flux density of 0.1/nm 2 /s and an average speed of ∼2 × 10 5 m/s were applied to the monolayer MoS 2 FET sample for 60 s. 44 A constant H 2 flow rate of 50 sccm kept the chamber pressure around 1.16 Torr. An electric field of 2.4 × 10 4 V/m was applied to the H 2 gas to ionize and accelerate the protons (the Methods section).…”

Interface Engineering by Intermediate Hydrogen Plasma Treatment Using Dc-PECVD for Silicon Heterojunction Solar Cells

“…However, upon annealing, it improves significantly to 1230 μs. For comparison, we have also shown results of Post-HPT discussed in our earlier work 31 and carried out the deposition at the same pressure of 2.5 Torr as for both I-HPT conditions reported here. Note that from Figure 1a, the τ eff of single-HPT is greater than double-HPT by ∼130 μs before annealing, whereas after annealing, double-HPT has a lifetime of ∼250 μs greater than single-HPT.…”

Optimization of Silicon Heterojunction Interface Passivation on p‐ and n‐Type Wafers Using Optical Emission Spectroscopy

“…[ 22–30 ] Recently, research has been conducted to determine the relation between optical emission spectra and surface passivation for SHJ solar cells. The main research areas can be classified as: quantification of the silane depletion fraction (or crystallization rate index), [ 31–33 ] postdeposition HPT, [ 34,35 ] predeposition treatments (i.e., tuning the background environment of the chamber), [ 36,37 ] and the impact of plasma ignition [ 38 ] on passivation quality.…”