Emitter saturation current densities of 22 fA/cm² applied to industrial PERC solar cells approaching 22% conversion efficiency

Abstract

Passivated Emitter and Rear Cells (PERC) are currently being introduced into mass production. The conversion efficiency of industrial p-type PERC cells is limited by the emitter saturation current density of around 90 fA/cm 2 of conventional homogeneously POCl 3 diffused emitters. In this paper we investigate two alternative emitter formation technologies. The first approach named in-situ oxidation inserts a short thermal oxidation in-between the phosphorus silicate glass deposition and the drive-in of a conventional homogeneous POCl 3 diffusion thereby reducing the phosphorus surface concentration. The second approach named Gas Phase Etch Back (GEB) selectively removes around 40 nm of the highly doped surface of the POCl 3 diffused emitter by the reactive gas phase of the wet chemical rear polishing bath. Whereas the conventional POCl 3 emitter exhibits a phosphorus surface doping concentration of 3 × 10 20 cm À3 , the in-situ oxidation and the GEB process reduce the doping concentration to 7 × 10 19 cm À3 and 4 × 10 19 cm À3 , respectively. Accordingly, the emitter saturation current density is reduced to excellent values of 22 fA/cm 2 (in-situ oxidation) and 28 fA/cm 2 (GEB) compared with 89 fA/cm 2 for the reference POCl 3 diffusion. Whereas the reference POCl 3 emitter limits the PERC conversion efficiency η to 21.1% and the open circuit voltage V oc to 655 mV, the in-situ oxidation improves the PERC current-voltage parameters up to 21.3% and 663 mV. The highest efficiency of 21.6% is obtained with the selective GEB emitter. When solving series resistance issues with the most advanced GEB emitter, the measured V oc and J sc values would support PERC conversion efficiencies up to 21.9%.

Efficient silicon nitride SiNx:H antireflective and passivation layers deposited by atmospheric pressure PECVD for silicon solar cells

“…Indeed, the correlated emitter saturation current density was higher for AP‐PECVD SiN x layers ( j 0e = 74 ± 2 fA.cm −2 ) than for LP‐PECVD films ( j 0e = 52 ± 1 fA.cm −2 ). Nevertheless, such j 0e value is relatively low if compared with state‐of‐the‐art published values, which demonstrates competitive SiN x emitter passivation properties while having still some room for its improvement through AP plasma optimization. For instance, the development of RF discharges modulated through TVW may lead to better film conformity and passivation properties.…”

“…Besides, SiN x layers offer good passivation quality on phosphorus‐doped n + emitters, which is measured by the emitter saturation current density ( j 0e ) and is currently reaching values lower than j 0e = 100 fA.cm −2 for standard 80 to 100 Ω/sq. emitters after RTA . However, a high positive Q f present in the SiN x layer is found to be detrimental for the passivation of boron highly doped p + emitters on n‐type solar cell architectures or back surface field (BSF) present in p‐PERC or p‐PERT solar cell architectures, as it induces a depletion layer near the surface which increases the charge carrier recombination rate .…”

“…Thus, significant cost reduction could be achieved by developing alternative processes in order to minimize wafer handling and avoid vacuum processes. For instance, PERC solar cells currently require three vacuum‐based processes for the deposition of the passivation layers: SiN x ARC on the front side and AlO x /SiN x passivation stack layers on the rear side . AlO x thin film providing high quality rear passivation properties can already be deposited at atmospheric pressure by using high‐throughput spatial ALD technique .…”

Effects of Iodine Doping on Carrier Behavior at the Interface of Perovskite Crystals: Efficiency and Stability

“…Compared with silicon solar cells [10][11][12], perovskite solar cells have simplified manufacture processing, and can be rapidly fabricated by spin-coating with precursor solutions of lead (II) iodide and methylamine hydroiodide (MAI). After only a few years of development, perovskite solar cells have reached a comparable efficiency to that of crystalline silicon solar cells [13].…”

Efficiency enhancement of bifacial PERC solar cells with laser‐doped selective emitter and double‐screen‐printed Al grid

“…After damage etching, alkaline texturing, and RCA cleaning, homogeneous emitter is diffused in a liquid phosphorus oxychloride (POCl 3 ) diffusion tube. To remove the dead layer, the conventional POCl 3 diffusion is modified to include a 15‐minute thermal oxidation step by using O 2 gas between the PSG deposition and the drive‐in . The doping profiles are measured by electrochemical capacitance‐voltage (ECV) profiling (CVP21, WEP, Germany).…”