Process–Structure–Properties Relationships of Passivating, Electron‐Selective Contacts Formed by Atmospheric Pressure Chemical Vapor Deposition of Phosphorus‐Doped Polysilicon

Abstract

Herein, we investigate the process–structure–properties relationships of in situ phosphorus (P)‐doped polycrystalline silicon (poly‐Si) films by atmospheric pressure chemical vapor deposition (APCVD) for fabricating poly‐Si passivating, electron selective contacts. This high‐throughput in‐line APCVD technique enables to achieve a low‐cost, simple manufacturing process for crystalline silicon (c‐Si) solar cells featuring poly‐Si passivating contact by excluding the need for vacuum/plasma environment, and additional post‐deposition doping steps. A thin layer of this P‐doped poly‐Si is deposited on an ultrathin (1.5 nm) silicon oxide (SiO x ) coated c‐Si substrate to fabricate the passivating contact. This is followed by various post‐deposition treatments, including a high‐temperature annealing step and hydrogenation process. The poly‐Si films are characterized to achieve a better understanding of the impacts of deposition process conditions and post‐deposition treatments on the microstructure, electrical conductivity, passivation quality, and carrier selectivity of the contacts which assists to identify the optimal process conditions. In this work, the optimized annealing process with post‐hydrogenation yields passivating contact with a saturation current density (J 0) of 3 fA cm−2 and an implied open‐circuit voltage (iV OC) of 712 mV on planar c‐Si wafer. Junction resistivity values ranging from 50 to 260 mΩ cm2 are realized for the poly‐Si contacts processed in the optimal annealing condition.

Single‐Gate In‐Transistor Readout of Current Superposition and Collapse Utilizing Quantum Tunneling and Ferroelectric Switching

“…The current networks within different nanosheets are expected to be influenced by the varying silicon nanograin assemblies. The average grain size of our polysilicon nanosheets was estimated to be ≈ D = 12 nm by analyzing the full width at half maximum of the 2 θ = 28.5° peak in the measured grazing incidence X‐ray diffraction (GIXRD) spectrum (where θ is the diffraction angle), [ 37 ] as described in our previous report. [ 38 ] This estimation aligns with the scale obtained from the TEM images (Figure 1c).…”

Silver Metallization with Controlled Etch Stop Using SiOx Layers in Passivating Contacts for Improved Silicon Solar Cell Performance

“…[22,23] Besides the inline concept, a fundamental technical deviation from other deposition methods is the deposition temperature, which is >650 °C for APCVD coatings. [24] Process temperature of other deposition technologies of a-Si like plasma-enhanced chemical vapor deposition (PECVD) or magnetron sputtering is usually not above 400 °C. [25,26] This temperature difference results in some significant changes in the deposited a-Si layer structure.…”

“…In particular, the crystallinity and the crystallite size of APCVD a-Si layers after crystallization is rather larger than that of PECVD, low-pressure chemical vapor deposition (LPCVD), or sputtered a-Si which has mostly a crystallite size <20 nm. [24,25] This influences in particular the conductivity, which especially increases with larger crystallites (therefore less grain boundaries, which are mostly limiting the conductivity) and has a much stronger influence on the conductivity than, for example, the doping level. [24,27] Due to the equipment design of inline APCVD tools, a layer thickness change can be carried out on the one hand by varying the belt speed or on the other hand by multiple drive-through (DT) in the equipment.…”

“…[24,25] This influences in particular the conductivity, which especially increases with larger crystallites (therefore less grain boundaries, which are mostly limiting the conductivity) and has a much stronger influence on the conductivity than, for example, the doping level. [24,27] Due to the equipment design of inline APCVD tools, a layer thickness change can be carried out on the one hand by varying the belt speed or on the other hand by multiple drive-through (DT) in the equipment. Using the DT approach, a native oxide grows when the sample cools down under air atmosphere after it passes the deposition section.…”

“…[ 24,25 ] This influences in particular the conductivity, which especially increases with larger crystallites (therefore less grain boundaries, which are mostly limiting the conductivity) and has a much stronger influence on the conductivity than, for example, the doping level. [ 24,27 ]…”