Recombination processes in passivated boron-implanted black silicon emitters

Abstract

Recombination processes in passivated boron-implanted black silicon emitters In this paper, we study the recombination mechanisms in ion-implanted black silicon (bSi) emitters and discuss their advantages over diffused emitters. In the case of diffusion, the large bSi surface area increases emitter doping and consequently Auger recombination compared to a planar surface. The total doping dose is on the contrary independent of the surface area in implanted emitters, and as a result, we show that ion implantation allows control of emitter doping without compromise in the surface aspect ratio. The possibility to control surface doping via implantation anneal becomes highly advantageous in bSi emitters, where surface passivation becomes critical due to the increased surface area. We extract fundamental surface recombination velocities S n through numerical simulations and obtain the lowest values at the highest anneal temperatures. With these conditions, an excellent emitter saturation current (J 0e ) is obtained in implanted bSi emitters, reaching 20 fA/cm 2 6 5 fA/cm 2 at a sheet resistance of 170 X/sq. Finally, we identify the different regimes of recombination in planar and bSi emitters as a function of implantation anneal temperature. Based on experimental data and numerical simulations, we show that surface recombination can be reduced to a negligible contribution in implanted bSi emitters, which explains the low J 0e obtained. Published by AIP Publishing. [http://dx

Impact of black silicon on light‐ and elevated temperature‐induced degradation in industrial passivated emitter and rear cells

“…In our experiments, the non‐textured edges of the SiN x ‐passivated b‐Si cells show more pronounced degradation in the PL map (Figure C) than the thicker acidic‐textured cells (Figure F). Hence, the magnitude of LeTID in our cells seems to scale rather with surface area than wafer thickness: b‐Si cells with the largest surface area (ratio to polished surface S f ≈ 5–7) experience the weakest degradation, followed by acidic‐textured cells ( S f ≈ 2), and the strongest LeTID is shown at the edges of b‐Si cells, which were chemically polished by SDR. Nevertheless, we want to stress that the heavy silicon consumption is a feature of the specific b‐Si etching process used in this study and could be drastically reduced by further optimization of the DRIE process.…”

Modeling Field Effect in Black Silicon and Its Impact on Device Performance

“…The IQE is simulated by applying a 2 mm wide light beam with a 10 mW/cm 2 power density perpendicular to the active area, similar to the actual measurement, and simulating the output current. Excellent chemical surface passivation from the Al2O3 is assumed by setting the surface recombination velocity (SRV) of electrons (Sn) and holes (Sp) both to 1×10 5 cm/s [21] on all Si-Al2O3 interfaces. Since the IQE cannot directly be measured from actual components, the comparison between simulated and experimental performance is done as external quantum efficiency (EQE).…”

“…Instead, the Sp and Sn discussed here are the fundamental surface recombination velocities of electrons and holes caused by trap states in the bandgap. Here, 1×10 5 cm/s corresponds to a surface with excellent chemical passivation obtained with SiO2 or Al2O3 [21], whereas 1×10 7 cm/s represents a highly recombining silicon-metal interface [26].…”

Black silicon back‐contact module with wide light acceptance angle

“…One of the major drawbacks of b‐Si is the difficulty to passivate the textured surface because of the high aspect ratio of nanostructures and the increase of Auger recombination in doped b‐Si regions due to high doping concentrations . In the last years, many efforts have been applied to obtain low recombination black silicon surfaces using either doped or nondoped nanostructures .…”

“…One of the major drawbacks of b-Si is the difficulty to passivate the textured surface because of the high aspect ratio of nanostructures and the increase of Auger recombination in doped b-Si regions due to high doping concentrations. 8 In the last years, many efforts have been applied to obtain low recombination black silicon surfaces using either doped or nondoped nanostructures. [9][10][11][12] For instance, MACE technique has been successfully applied to large-area both-side contacted DWS mc-Si or CZ c-Si solar cells with efficiencies more than 19% using phosphorous-doped b-Si passivated with plasma-enhanced chemical vapor deposition (PECVD) SiN x.…”