Rapid Vapor-Phase Direct Doping for High-Efficiency Solar Cells

Abstract

An alternative boron emitter diffusion process called rapid vapor-phase direct doping (RVD) is studied and applied to n-type silicon solar cells with a tunnel oxide passivated electron contact (TOPCon). The RVD emitter diffusion process occurs under an atmosphere containing only the dopant gas and hydrogen. Thus, compared with standard tribromide diffusion processes, no oxygen is present. Hence, no boron glasses form during the RVD process. Consequently, a faster diffusion process with fewer chemical treatments after the diffusion process compared with standard tribromide processes is possible. In this paper, three different RVD emitter surface dopant concentrations and dopant depths were achieved by process parameter variations. These RVD emitters were applied to TOPCon cells, and their cell characteristics were compared with profiles of TOPCon reference cells with standard boron-diffused emitters. Up to 24.0% cell efficiency, 697.6 mV open-circuit voltage, 41.8 mA/cm 2 short-circuit current density, and 82.1% fill factor were reached by the best TOPCon cell with an RVD emitter. Nevertheless, compared with the reference, all cells with RVD emitters exhibited efficiency losses. Hence, to further optimize cells with RVD emitters, in-depth characterizations were conducted. The cell efficiency of cells with an RVD emitter is mainly limited by two main reasons: First, effective carrier lifetime degradation was observed, resulting in voltage losses, and second, for RVD diffusion temperatures above 980 • C, a flattening of textured cell surfaces was detected leading to current losses. In order to overcome these issues, an adapted two-step RVD emitter diffusion process is suggested for future experiments.

Simultaneous Boron Emitter Diffusion and Annealing of Tunnel Oxide Passivated Contacts Via Rapid Vapor-Phase Direct Doping

“…Compared to previous results with homogeneous emitters [9] the short circuit current J SC is increased the process temperature lowered, and reflection properties are not affected by flattened pyramids. However, previous cells had a higher open circuit voltage V OC of 703 mV and a FF of 82.8%.…”

“…n-type TOPCon cells with B-RVD emitters as schematically shown in Fig. 1 were already successfully realized using a sequential process with emitter diffusion on the front side prior to the TOPCon processes on the rear side [9]. These cells reached a high efficiency of up to 23.9% for a homogeneous emitter diffused at 1030 °C, which demonstrates the potential of RVD.…”

“…formation process is the rapid vapor-phase direct doping (RVD) process [7]- [9]. In contrast to the conventional BBr 3 diffusion, RVD diffusion is not carried out in oxygen containing atmosphere but pure hydrogen and diborane (B 2 H 6 ) is used as boron precursor.…”

AFORS-HET-based numerical exploration of tunnel oxide passivated contact solar cells incorporating n- and p-type silicon substrates

“…The same apparatus that is used for the fabrication of PERC solar cells can also be used for manufacturing the TOPCon structure. 21,22 The manufacturing of the TOPCon structure is more straightforward than that of the PERC solar cells, as there is complete passivation and metal contact at the rear side. During the fabrication route of TOPCon devices, thin layers of tunnel oxide and highly doped polycrystalline-silicon (poly-Si) are deposited, effectively minimizing the charge carrier recombination.…”

Numerical analysis of p-type and n-type based carrier-selective contact solar cells with tunneling oxide thickness and bulk properties

“…A TOPCon solar cell is uniform with rear cell structure, providing 1D carrier transport and carrier-selective contact, and therefore, high V OC (open-circuit voltage) and FF. Previous works on TOPCon solar cells, involving both experimental and theoretical aspects, were mainly studies of process developments aimed at cell fabrication: evaluations of substrate temperature using plasma-grown tunnel oxide 13) and passivation quality with annealing temperature, 14) comparison of oxidation processes for growing tunnel oxide with passivation quality and contact resistivity, 15) recombination analysis using numerical simulation, 16) application of rapid vaporphase direct doping process to TOPCon solar cells, 17) TOPCon solar cell process using ion implantation and evaluation of process conditions, 18) and demonstrations of multi-crystalline n-type TOPCon solar cell with recombination, lifetime mapping, and comparison of manufacturing processes. 19) Choi et al reported the refined TOPCon solar cell structure combined with amorphous silicon.…”