Process‐Structure‐Properties Relationships of Passivating, Electron‐Selective Contacts Formed by APCVD of Phosphorus‐Doped Polysilicon

In this work, the process-structure-properties relationships of phosphorus doped polycrystalline silicon (poly-Si) films formed by atmospheric pressure chemical vapor deposition (APCVD) are investigated. These films can be used to form passivating, electron selective contacts for crystalline silicon (c-Si) solar cells. Unlike other CVD processes like LPCVD and PECVD, this in-line APCVD is a single side deposition process which does not require vacuum systems or a plasma environment. This high-throughput process also leverages in situ doping, excluding the need for an additional post-deposition doping step. A passivating, electron selective contact is formed by depositing a thin layer of in situ phosphorus doped silicon (Si) using the APCVD process on a chemically grown ultrathin (1.5 nm) silicon oxide (SiOx) coated c-Si substrate. This is followed by various post-deposition treatments, including a high temperature annealing step and hydrogenation process. The microstructure, electrical conductivity, and passivation quality of the films are characterized for different deposition temperatures, deposition gas ratios, post-deposition annealing temperatures, and with/without a post-deposition hydrogenation process. The contact and junction resistivity are also measured on a subset of samples. By assessing the correlation between process, structure, properties, and performance of these poly-Si passivating contacts, optimal process conditions are identified to fabricate high quality electron selective contacts with excellent surface passivation quality and low junction resistivity using the APCVD process. In this study, the optimized annealing process with post-hydrogenation yields a passivating contact with recombination current density (J0) as low as 3 fA/cm2 and an implied open circuit voltage (iVOC) of 712 mV on a planar c-Si wafer. Junction resistivity values ranging from 50 mΩ⋅cm2 to 260mΩ⋅cm2 are realized for the oxide-passivated APCVD poly-Si contacts processed in theThis article is protected by copyright. All rights reserved.