Record fast thermal processing of 17.5  efficient silicon solar cells

Abstract

This paper presents the development and analysis of 17.5% efficient silicon solar cells on 0.9 cm PV-grade Czochralski silicon (Cz-Si), featuring a record small thermal process time of 1 min for diffusion and oxidation. The cells have been processed by rapid thermal processing (RTP) using incoherent light as an energy source. The involved processes consist of a 5 s RTP step at 930 • C for the simultaneous formation of the phosphorus-doped emitter and of the aluminium back surface field (Al-BSF) and a 30 s rapid thermal oxidation (RTO) at 950 • C for the emitter surface passivation. Both processes feature high heating and cooling rates of 100 K s −1 . The results show that no lengthy gettering or post diffusion annealing steps are required for the fabrication of high efficiency Cz-Si solar cells and that high heating and cooling rates are applicable. Detailed analysis reveals that the emitter saturation current J 0e is reduced by a factor of 3-4 after the RTO passivation in spite of the high carrier surface concentrations of 3 to 4 × 10 20 cm −3 . Furthermore, one-dimensional device simulations are presented which show that the achieved efficiencies are limited by the effective back surface recombination velocity S back resulting from the thin Al-BSF applied.

Formation of shallow boron emitters in crystalline silicon using flash lamp annealing: Role of excess silicon interstitials

“…The presence of two components in the 00.2 transverse x-scan can be related to: (i) a substrate surface related streak overlapping with the film signal, 32 (ii) an unconventional mosaic structure of the film with the single crystallites coherently scattering the X-rays because of a long range order due to the substrate film interfacial interactions. 33 In the latter case, the specular component is attenuating at high reflection orders due to the residual disorder present, whereas in the former case, it disappears due to the increasing angular distance between the substrate/film peak positions. Both interpretations are consistent with the results obtained, and further measurements are necessary to distinguish between the two physical mechanisms.…”

“…A common strategy in industry for fabricating emitters is through diffusion from a gas source in a tube furnace [31,32], but this requires prolonged heat treatments which deepens the emitter and reduces the blue response. Several rapid heat treatment schemes such as RTA [29,33,34], Excimer Laser Annealing (ELA) [35,36] and FLA [28,37] have successfully been employed to realize very shallow emitters with high doping concentrations. Perhaps the most efficient of these is ELA where a high intensity laser melts a very thin layer (∼ 150 nm [38]) close to the surface greatly enhancing the diffusion of dopants producing a box like diffusion profile with very high dopant concentrations.…”

“…However, this technique requires expensive low energy ion implantation and suffers from low throughput since the laser only heats the wafer locally. A higher throughput strategy for fabricating shallow emitters is using RTA to heat up wafers and in-diffusing dopants from a surface source [29,33,34]. This technology has the advantage of being able to treat several wafer simultaneously in a matter of seconds, but as seen in the inset of Fig.…”

Surface Passivation and Carrier Collection in {110}, {100} and Circular Si Microwire Solar Cells

“…The tapering leads to grading of effective refractive index that is known to enhance optical absorption in 1D nanowires. [41] For the SiMWs, the SIMS was carried out on three different locations of a single SiMW sidewall: top (1 µm below the tip of SiMW), center (5 µm below the tip of SiMW), and bottom (1 µm above the base of SiMW) as shown in Figure 4b. The lower surface peak concentration and the broadening of x j for the passivated planar cell are attributed to the redistribution of phosphorus dopants during thermal oxidation where phosphorus atoms diffuse to deeper Si during thermal oxidation.…”

Physically Based Analytical Model of Heavily Doped Silicon Wafers Based Proposed Solar Cell Microstructure

“…Still, few research works have been done to fabricate silicon-based solar cells in a cheap way with a relatively high efficiency [6][7][8][9]. One of the most interesting attempts to get high efficiency low cost silicon-based cells is to use a nanorod with a high-doped pn junction in the radial direction [10,11].…”