High-efficiency selective boron emitter formed by wet chemical etch-back for n-type screen-printed Si solar cells

Abstract

Front metal contact induced recombination and resistance are major efficiency limiting factors of large-area screen-printed n-type front junction Si solar cells with homogeneous emitter and tunnel oxide passivated back contact (TOPCON). This paper shows the development of a selective boron emitter (p+/p++) formed by a screen-printed resist masking and wet chemical etch-back process, which first grows a porous Si layer and subsequently removes it. Various wet-chemical solutions for forming porous Si layer are investigated. An industrial compatible process with sodium nitrite (NaNO2) catalyst is developed to uniformly etch-back the ∼47 Ω/◻ atmospheric pressure chemical vapor deposited heavily doped boron emitter to ∼135 Ω/◻ by growing a 320 nm porous Si layer within 3 min and subsequently removing it. After etching back, the boron emitter was subjected to a thermal oxidation to lower the surface concentration and the emitter saturation current density J0e. Various etched-back emitters were evaluated by measuring J0e on symmetric test structures with atomic layer deposited aluminum oxide (Al2O3) passivation. Very low J0e of 21, 14, and 9 fA/cm2 were obtained for the 120, 150, and 180 Ω/◻ etched-back emitters, respectively. A solar cell with a selective emitter (65/180 Ω/◻) formed by this etch-back technology and with an Al/Ag contact on the front and TOPCON on the back gave an open-circuit voltage (Voc) of 682.8 mV and efficiency of 21.04% on n-type Czochralski Si wafer. This demonstrates the potential of this technology for next generation high-efficiency industrial n-type Si solar cells.

Correlation between Boron–Silicon Bonding Coordination, Oxygen Complexes and Electrical Properties for n-Type c-Si Solar Cell Applications

“…In this regard, optimization of diffusion technology to form good-quality p-n junctions is the basis for realizing the high-efficiency potential of n-types and must be emphasized in the future. This is because the formation of p + diffused layers using BBr 3 is expected to maintain about 85% of the market share until 2029, as there is no viable alternative available [3, [9][10][11].…”

TiO2–x-Enhanced IR Hot Carrier Based Photodetection in Metal Thin Film–Si Junctions

“…E xtracting energetic carriers from light absorption in socalled hot carrier Schottky barrier (SB) junctions has attracted enormous attention, as it allows harvesting low photon energies that have so far been omitted from semiconductor photodetectors. 1−8 Since metals offer zero bandgap energy, their operation can in principle cover visible, mid-infrared, terahertz, and microwave regimes, which holds great promises for gas detection, 9,10 imaging sensors, 11 wavelength determination, 12,13 power monitoring, 14 and sustainable power supplies. 15−17 Taking silicon photodetectors (with a bandgap energy of 1.1 eV) 18 for instance, exploitation of SB devices can result in a highly integrated CMOScompatible and inexpensive alternative to commercially used germanium (Ge) and gallium arsenide (GaAs) photodetectors at telecommunication wavelengths.…”

Unlocking the potential of boronsilicate glass passivation for industrial tunnel oxide passivated contact solar cells

“…In recent years, extensive studies on boron emitter passivation with different films and deposition methods have been reported, such as by thermal SiO 2, 22,23 atomic layer deposited (ALD) TiO 2, 24 ALD Al 2 O 3, 25,26 ALD Al 2 O 3 /TiO 2 stacks, 27,28 plasma‐enhanced ALD (PEALD) Al 2 O 3 /plasma‐enhanced chemical vapor deposited (PECVD) SiN x , 29 atmospheric pressure chemical vapor deposition (APCVD) Al 2 O 3 /PECVD SiN x , 29 PECVD AlO x /SiN x , 30–32 PECVD SiO x /SiN x , 33 and PECVD SiON/SiN x . 34 However, there have been very few reports using boronsilicate glass (BSG) as a passivating film, especially on a textured surface with device applications.…”