Poly‐SiO_x Passivating Contacts with Plasma‐Assisted N₂O Oxidation of Silicon (PANO‐SiO_x)

Abstract

Passivating contacts are crucial for realizing high‐performance crystalline silicon solar cells. Herein, contact formation by plasma‐enhanced chemical vapor deposition (PECVD) followed by an annealing step is focused on. Poly‐SiOx passivating contacts by combining plasma‐assisted N2O‐based oxidation of silicon (PANO‐SiOx) with a thin film of phosphorus (n+) or boron (p+)‐doped hydrogenated amorphous silicon oxide (a‐SiOx:H) are manufactured. Postannealing is conducted for transitioning a‐SiOx:H into poly‐SiOx. The aim is to achieve a contact with low absorption and high‐quality passivation. It is demonstrated that by tuning the plasma oxidation process time and power, the PANO‐SiOx thickness and its passivation quality can be controlled. A higher SiO2 content is observed in PANO‐SiOx than in the nitric acid oxidation of silicon (NAOS‐SiOx) counterpart. PANO‐SiOx acts as a stronger diffusion barrier for both boron and phosphorus atoms compared to NAOS‐SiOx, affecting the dopant distribution during annealing. Implied open‐circuit voltages up to 751 and 710 mV for n+ and p+ flat symmetric samples, respectively, are demonstrated. With respect to standard thermally grown SiO2 tunneling oxide combined with (in/ex )situ‐doped low‐pressure chemical vapor deposition poly‐Si, this study presents a simple alternative for manufacturing passivating contact fully based on PECVD processes.

Plasma‐Enhanced Chemical‐Vapor‐Deposited SiOx(Ny)/n‐type Polysilicon‐on‐Oxide‐Passivating Contacts in Industrial Back‐Contact Si Solar Cells

“…Input parameters given in the second column “Reference case” of Table 3 represent the current status of our solar cells, which have been derived from experimental test structures processed with the POLO IBC solar cells as mentioned in the third column. To simulate the bulk lifetime of the Ga‐doped bulk material, we use the parameterization of Boron Oxygen‐deactivated defect complex given in ref 11. as this parameterization gave a good fit to experimental lifetime samples of Ga material.…”

“…The application of PECVD processing for both layers, the interfacial oxide and the amorphous silicon, [ 9–11,13 ] offers the option to realize a very lean process flow and uses low processing temperatures, which is beneficial to retain high silicon bulk lifetimes.…”

“…The passivating contact technology based on polysilicon (poly‐Si) combined with a 1–2 nm thin interfacial silicon oxide which is often called POLy‐silicon on Oxide (POLO) [ 1 ] and tunnel‐oxide‐passivated contact [ 2 ] technology is expected to become the mainstream in industrial silicon solar cells within the next 5–8 years as stated by the International Technology Roadmap for Photovoltaic roadmap. [ 3 ] Several different techniques for interfacial oxide fabrication as well as amorphous Si deposition (which is later on transformed to poly‐Si by an annealing step) have been investigated within the last years: thermal, [ 4 ] wet–chemical, [ 5 ] and plasma‐enhanced chemical vapor deposition (PECVD) [ 6,12 ] processes are used for interfacial oxide growth, whereas low‐pressure chemical vapor deposition (CVD), [ 2,4 ] physical vapor deposition by sputtering, [ 7 ] atmospheric‐pressure CVD, [ 8 ] and plasma‐enhanced CVD [ 9–11 ] are some of the options to deposit the amorphous Si layer on top of the oxide.…”