Passivation of Phosphorus Diffused Black Multi‐Crystalline Silicon by Hafnium Oxide

Abstract

A key challenge for the success of the recent trend to adopt diamond wire sawing for multi-crystalline silicon wafers is the texturing and passivation of their surfaces. The various so-called "black silicon" texturing technologies show great promise in providing strong optical gains, but the nano-scale surface structures resulted from dry etching are challenging to passivate with the conventional plasma enhanced chemical vapor deposition of silicon nitride. In this work, a single layer of atomic layer deposited hafnium oxide, in combination with a short anneal, has been used to demonstrate not only low surface recombination on reactive ion etched and phosphorus diffused (90 Ω/&) surfaces but also effective passivation of bulk defects in p-type 1.5 Ω cm multi-crystalline silicon wafers. A combination of photoluminescence imaging and quasi-steady state photoconductance measurements shows that the recombination via bulk defects such as grain boundaries is mitigated due to hydrogenation during rapid thermal annealing at mid to high temperatures in nitrogen. A further activation anneal at low temperature following hydrogenation improves the effective carrier lifetime by 40%. A recombination current density of J 0nþ ¼ 98 fA cm À2 per side at an injection level of Δn ¼ 10 15 cm À3 has been obtained, which equates to an attainable 1-sun implied open circuit voltage of 691 mV when bulk and rear surface recombination are excluded. These results prove that hafnium oxide offers a viable alternative for passivating the surface and the bulk of multi-crystalline silicon solar cells.

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

“…It is particularly important for multicrystalline silicon (mc‐Si) solar cells, as mc‐Si material inherently contains extended crystal defects such as grain boundaries (GBs) and dislocation clusters and also has relatively high metal impurity concentrations . Common methods for incorporating hydrogen into Si for bulk passivation include (a) in diffusion from hydrogen‐rich dielectric films, (b) hydrogen ion implantation, (c) hydrogen plasma treatment, and (d) annealing in a hydrogen ambient . Among these, high‐temperature rapid annealing of amorphous silicon nitride (SiN x ) is the most widely used hydrogenation method in photovoltaic (PV) manufacturing.…”

Silicon Passivation by Ultrathin Hafnium Oxide Layer for Photoelectrochemical Applications

“…Passivation in photovoltaics (PV) and electrochemistry refers to different, albeit related, phenomena. Electronic passivation in PV addresses reduction of interface state density (D if ) (unsaturated bonds) on the semiconductor surface, for example, by chemical reduction applying passivating dielectrics (Cui et al, 2017a;Singh et al, 2016;Oudot et al, 2018). Another important type is the field effect passivation, which relates to electrostatic shielding of the charge carriers from the interface by an internal electric field, for example, films having a negative (Al 2 O 3 , SiO 2 +HfO 2 ) or positive (SiN x ) charge (Singh et al, 2016;Oudot et al, 2018).…”

“…Hafnia films were obtained by various techniques such as RF and DC magnetron sputtering (Verelli and Tsoukalas, 2011;Dave et al, 2018), electrochemical anodizing (Fohlerova and Mozalev, 2019), electron beam evaporation (Ramzan et al, 2015), ultrasonic spray pyrolysis (Mendoza et al, 2010), UVstimulated plasma anodizing (Kushitashvili et al, 2017), pulsed laser deposition (Plociennik et al, 2014), and electrochemical formation in organic electrolytes (Wang et al, 2017). Atomic layer deposition (ALD) is most widely used to form thin hafnia films and microstructures (Polydorou et al, 2018;Cui et al, 2017a;Singh et al, 2016;Oudot et al, 2018;Chen et al, 2010;Li et al, 2019;Zhang et al, 2017b;Ortiz-Dosal et al, 2017;Gaskins et al, 2017;Berdova and Liu, 2016). Thermal, mechanical, electrical, optical, and structural properties of ALD-formed HfO 2 have recently been investigated and reviewed (Gaskins et al, 2017;Berdova and Liu, 2016;Jogiaas et al, 2015).…”