Investigation on the passivated Si/Al2O3 interface fabricated by non-vacuum spatial atomic layer deposition system

Abstract

Currently, aluminum oxide stacked with silicon nitride (Al2O3/SiNx:H) is a promising rear passivation material for high-efficiency P-type passivated emitter and rear cell (PERC). It has been indicated that atomic layer deposition system (ALD) is much more suitable to prepare high-quality Al2O3 films than plasma-enhanced chemical vapor deposition system and other process techniques. In this study, an ultrafast, non-vacuum spatial ALD with the deposition rate of around 10 nm/min, developed by our group, is hired to deposit Al2O3 films. Upon post-annealing for the Al2O3 films, the unwanted delamination, regarded as blisters, was found by an optical microscope. This may lead to a worse contact within the Si/Al2O3 interface, deteriorating the passivation quality. Thin stoichiometric silicon dioxide films prepared on the Si surface prior to Al2O3 fabrication effectively reduce a considerable amount of blisters. The residual blisters can be further out-gassed when the Al2O3 films are thinned to 8 nm and annealed above 650°C. Eventually, the entire PERC with the improved triple-layer SiO2/Al2O3/SiNx:H stacked passivation film has an obvious gain in open-circuit voltage (Voc) and short-circuit current (Jsc) because of the increased minority carrier lifetime and internal rear-side reflectance, respectively. The electrical performance of the optimized PERC with the Voc of 0.647 V, Jsc of 38.2 mA/cm2, fill factor of 0.776, and the efficiency of 19.18% can be achieved.

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

“…For iV oc samples and PERC solar cells, a 6-nm-thick Al 2 O 3 layer was then deposited on the rear-side by using ultrafast spatial ALD process. 16 This step was followed by the so-called outgassing process, which is a 10-minute low temperature annealing under N 2 at 550°C performed mainly to avoid blistering of the rear-side stack layer. 8 Next, the wafers were distributed into three different groups for the For iV oc experimental protocol (see Figure 4A), the samples were then fired in an IR-lamp belt furnace at a peak temperature of 820°C.…”

“…5 Thus, the surface passivation of such p + emitter/BSF is generally realized by applying either ultrathin (<10 nm) silicon oxide (SiO x ) or aluminum oxide (AlO x ) layers, which are usually capped by a thicker protective SiN x film (70-150 nm). [14][15][16] Particularly, AlO x /SiN x stacks lead to very low SRV (≤10 cm.s −1 ) on moderately doped n-type and p-type Si wafers and correspondingly low j 0e (≤ 50 fA.cm −2 ) on p + emitter/BSF. 15,16 While ultrathin AlO x layers may be deposited by atomic layer deposition (ALD) or LP-PECVD, the SiN x capping layer is usually deposited by LP-PECVD.…”

“…8,9 AlO x thin film providing high quality rear passivation properties can already be deposited at atmospheric pressure by using high-throughput spatial ALD technique. 16 However, a technological bottleneck for increasing the solar cell production throughput is the deposition of SiN x thin layers at atmospheric pressure conditions. Indeed, such a process would be compatible with a fully in-line solar cell fabrication process and would avoid the need for an expensive vacuum equipment.…”

Surface Passivation of Silicon Using HfO2 Thin Films Deposited by Remote Plasma Atomic Layer Deposition System

“…Besides SiO 2 , other layers such as SiC, a-Si:H and Si 3 N 4 have been used for surface passivation [1]. Recently, Al 2 O 3 films that are grown by atomic layer deposition (ALD) have been demonstrated to provide good surface passivation on c-Si [2–4]. ALD technique is a powerful method.…”

Evidence for efficient passivation of vertical silicon nanowires by anodic aluminum oxide

“…By controlling the deposition time and plasma power of hydrogenated amorphous silicon deposition, the effective carrier lifetime of 0.51-µm-Si nanowires is around 6 µs [10]. Recently, the Al 2 O 3 thin film was considered as a promising candidate of surface passivation thanks to both reduction in interface defects and formation of fixed charges upon postdeposition anneal [11][12][13]. The Al 2 O 3 thin film for passivation is generally deposited by means of plasma/ thermal Atomic Layer Deposition (ALD) or Chemical Vapor Deposition (CVD).…”