Comparison of firing stability between p‐ and n‐type polysilicon passivating contacts

Abstract

This work compares the firing response of ex‐situ doped p‐ and n‐type polysilicon (poly‐Si) passivating contacts and identifies possible mechanisms underlying their distinct firing behavior. The p‐type poly‐Si shows greater firing stability than n‐type poly‐Si, particularly at a higher firing temperature, which results in a substantial increase in the recombination current density parameter J0 from 9 to 96 fA/cm2 upon firing at 900°C for n‐type poly‐Si, in comparison to an increase from 11 to 30 fA/cm2 for p‐type poly‐Si. It is observed that p‐type poly‐Si contacts only suffer a slight degradation or even exhibit a small improvement in J0 after firing at 800°C, depending on the boron diffusion temperature. Secondary ion mass spectrometry (SIMS) results demonstrate that the hydrogen concentration near the interfacial SiOx increases with the peak firing temperature in n‐type poly‐Si, whereas the hydrogen profile remains unchanged for p‐type poly‐Si upon firing at various temperatures. Moreover, we observe that injecting additional hydrogen into the poly‐Si/SiOx stacks fired with SiNx coating layers further degrades n‐type poly‐Si, but recovers the J0 of p‐type poly‐Si to the value before firing. In contrast, removing hydrogen from the fired poly‐Si/SiOx stacks leads to an initial recovery and then a second degradation of J0 in n‐type poly‐Si, but no substantial impact on p‐type poly‐Si. It is hypothesized that the distinct difference in the firing impact on p‐ and n‐type poly‐Si is related to the different effective hydrogen diffusivity, which determines the hydrogen content surrounding the SiOx layer and hence the passivation quality after firing.

Electronic Characteristics of Ultra‐Thin Passivation Layers for Silicon Photovoltaics

“…[ 4,20 ] Although the optimum J 0 values calculated here based on the Niewelt model are marginally greater than 10 fA cm −2 , these results were obtained without any post‐deposition hydrogenation, common for passivating contacts. [ 3,9,12 ] Hence the determined J 0 values suggest HfO 2 has potential as a material for passivating contacts, and this is a topic of ongoing research.…”

“…Current passivating contacts often have to be fired at temperatures ≥900 °C to achieve reasonable passivation quality. [ 9 ] This work shows that it is possible to achieve good quality passivation with HfO 2 without needing to anneal at such high temperatures and without the presence of an a‐Si heterojunction, hence providing a potential route to lower thermal budget processing while maintaining contact stability.…”

“…Hence single-side J 0 values were obtained by dividing extracted J 0 by 2. [9] Contact potential difference (CPD) measurements were made with a KP Technologies SKP5050 Kelvin Probe with a 2 mm goldplated tip, based on the method of Baikie et al [60] A Fiber-Lite DC-950 Quartz Tungsten Halide lamp was used for surface photovoltage measurements. The light intensity measured at the sample location with a Thorlabs PM16-130 power meter was 12.22 W cm −2 at 635 nm.…”

“…[3,7,8] TOPCon is an efficient electron-selective contact but has a high thermal budget with temperatures around 900 °C needed to reduce the contact resistivity to acceptable levels. [9] An efficient hole-selective layer that can match or exceed the performance of the current electron-selective materials would be of considerable interest. The use of SiO 2 -based hole-selective contacts has so far failed to reach equivalent levels.…”

Optimum Hydrogen Injection in Phosphorus-Doped Polysilicon Passivating Contacts

“…J 0 degradation due to the presence of excess hydrogen was also observed on poly-Si structures fabricated with different processing, including ex situ doped PECVD and LPCVD poly-Si, LPCVD poly-Si deposited at various temperatures, and LPCVD poly-Si deposited on chemical and thermal oxide. 23,43 Therefore, it is anticipated that the proposed model can also be applied to differently processed poly-Si.…”