Preprint to be published in the proceedings of the 32 nd European Photovoltaic Solar Energy Conference, 20-24 June 2016, Munich, Germany EVALUATION OF SPATIAL ALD OF AL2O3 FOR REAR SURFACE PASSIVATION OF MC-SI PERC SOLAR CELLS Friederike Kersten, Ina Förster, Stefan Peters Hanwha Q CELLS GmbH Sonnenallee 17-21, 06766 Bitterfeld-Wolfen, Germany ABSTRACT: In this work the evaluation results on industrial p-type mc-Si PERC cells using spatial atomic layer deposition for aluminum oxide from SoLayTec are shown. By optimizing the process flow and integrating a post- deposition anneal into the SiNx capping process we achieve 0.15% higher cell efficiency compared to remote microwave plasma-enhanced chemical vapor deposition. Furthermore, it is shown that the improved passivation quality resulting in Voc gain remains constant during light and elevated temperature induced degradation measurements. Keywords: Multicrystalline Silicon, Passivation, Degradation. 1 INTRODUCTION Deposition of aluminum oxide (Al2O3) by an atomic layer deposition (ALD) process has been evaluated on a high throughput deposition tool from SoLayTec (“InPassion ALD”). The key features of this new deposition technology are high flexibility in layer thickness, high throughput due to a deposition rate of up to 1 nm/s with excellent uniformity and single sided deposition on standard 6“ solar wafers while maintaining proven superior surface passivation known from batch ALD. We evaluate the InPassion ultrafast spatial ALD tool from SoLayTec for industrial production of mc-Si solar cells based on Hanwha Q CELLS Q.ANTUM technology [4]. Only the rear side passivation layer was varied by using spatial ALD for Al2O3 deposition in comparison to remote microwave plasma-enhanced chemical vapor deposition (MW-PECVD) of AlOx. Based on recently published severe light-induced degradations levels of mc-Si PERC cells [1-3] the long- time performance stability of these ALD passivated mc-Si PERC cells during light and elevated temperature (LeTID) was investigated. 2 EXPERIMENTAL The in-line spatial ALD Al2O3 system from SoLayTec works with a gas mixture comprising of trimethylaluminium (TMAl) and water (H2O) vapor. The two process gases are separated by nitrogen (N2) gas curtains. In a high throughput ALD process both half- reactions are spatially separated, as shown by the sketch in Fig. 1. The wafers move contactless on nitrogen gas bearings and pass TMAl and H2O vapor inlets sealed off by a flow of pressurized N2, forming isolated reaction zones. The wafers move back and forth underneath the reactor head, each passage under the injector head results in two complete ALD cycles. The deposition rate is determined by the cycle rate of the wafer in the reactor, enabling deposition rates of up to 1 nm/s. In a conventional ALD reactor operating under vacuum conditions, pump and vent times can severely limit the wafer throughput. As the spatial ALD concept works under atmospheric pressure, any pump or vent times are avoided [5]. Subsequently to the Al2O3 deposition a post- deposition anneal (PDA) integrated into the deposition of the SiNx capping layer in a conventional tube furnace direct plasma PECVD was used. For performance stability measurements highly LeTID susceptible mc-Si wafer material was processed to 6” PERC solar cells. Part of the cells were passivated with MW-PECVD Al2O3 as reference batch. The other cells were passivated with SoLayTec InPassion ALD. The layer thickness was varied between 4.7, 10 and 20 nm ALD Al2O3. All cells were processed with a LeTID susceptible process flow. Only the PECVD batches and the 4.7 nm ALD Al2O3 cells were additional processed by using the LeTID controlled solar cell process sequence of Hanwha Q CELLS [3]. The LeTID treatments are carried out in Voc mode at 75°C. The excess carriers are injected by illumination at 1000 W/m 2 . After 800 h exposure time all cells were regenerated without illumination at 200°C for 10 min in muffle furnace. Figure 1: Sketch of in-line spatial ALD concept [6]. The TMAl and H2O half-reaction zones are separated by N2 curtains. Contactless transport of the wafer is facilitated by N2 gas bearings below the wafer.