Passivation of n‐type emitter and p‐type base in solar cells via oxygen terminated silicon nanoparticles

Abstract

Various measurements and experiments are performed to establish the mechanism of passivation on emitter and base of conventionally manufactured solar cell with p-type base. The surface coatings on the emitter are removed. The bare surface is then coated with silicon (Si) nanoparticles (NPs) with oxygen termination. It shows an increase in the cell efficiency up to 14% over bare surface of solar cell. The NPs show enhancement in light scattering from the surface, but shows an increase in the recombination lifetime indicating an improved passivation. When back contact is partially removed, the coating on bare back side ( p-type) of the solar cell also improves the cell efficiency. This is also attributable to the increased recombination lifetime from the measurements. Same NPs are seen to degrade the surface of n and p-type Si wafers. This apparently contradictory behaviour is explained by studying and comparing the emitter (n-type) surface of the solar cell with that of n-type Si wafer and the back surface ( p-type) with that of p-type Si wafer. The emitter surface is distinctly different from the n-type wafer because of the shallow p-n junction causing the surface depletion. Back surface has aluminium (Al) metal trace, which plays an important role in forming complexes with the oxygen-terminated Si NPs (Si-O NPs). With these studies, it is observed that increase in the efficiency can potentially reduce the thermal budget in solar cell preparation.

Construing the interaction between solar cell surface and fatty amine for the room temperature passivation

“…Silicon wafer were ultrasonically cleaned in acetone, and immersed in hydrofluoric acid (HF) solution (49% v/v Sigma Aldrich) for three seconds to remove native oxide layer. Removal of anti-reflection coating of crystalline silicon solar cell was also done with same HF as reported elsewhere (Patil et al, 2013b;Rajesh et al, 2012). The Oleylamine (OLA) was purchased from Sigma Aldrich (Tech.…”

“…Due to this, solar cell surface shows p-type characteristics. This facilitates active sites for induced passivation (Patil et al, 2013a).…”

“…Therefore the understating of passivation mechanism of n-emitter in presence of shallow p-n junction of solar cell is to be treated separately in contrast with the passivation mechanism of silicon wafer. A continued investigation of the surface coatings and nanoparticles interaction with the n-type emitter surface led to various coatings which showed varying efficiency toward passivation (Rajesh et al, 2012;Patil et al, 2013a) following, we show passivation results of organic Oleylamine (OLA) layer on n-emitter surface of solar cell. Application of OLA layer on the bare n-type emitter surface leads to a passivation comparable with SiO 2 or SiNx coatings on the commercial solar cells.…”