Abstract
Aluminum oxide films were deposited on crystalline silicon substrates by reactive RF magnetron sputtering. The influences of the deposition parameters on the surface passivation, surface damage, optical properties, and composition of the films have been investigated. It is found that proper sputtering power and uniform magnetic field reduced the surface damage from the high-energy ion bombardment to the silicon wafers during the process and consequently decreased the interface trap density, resulting in the good surface passivation; relatively high refractive index of aluminum oxide film is benefic to improve the surface passivation. The negative-charged aluminum oxide film was then successfully prepared. The surface passivation performance was further improved after postannealing by formation of an SiOxinterfacial layer. It is demonstrated that the reactive sputtering is an effective technique of fabricating aluminum oxide surface passivation film for low-cost high-efficiency crystalline silicon solar cells.
Highlights
As the surface passivation of reactive sputtered aluminum oxide lm is mainly limited by high interface traps density while xed negative charge of sputtered lms is similar to that deposited by atomic layer deposition (ALD) [7, 9, 10], proper sputtering parameters, proper sputtering power, for instance, can reduce the surface damage caused by highenergy ions bombardment during the process and result in the reduction of interface trap density
Comparing the minority carrier lifetime mappings with their corresponding PL images in Figure 1, it is found that the higher minority carrier lifetime regions are much brighter in all the samples, which shows that these regions get less surface damage from high-energy ions during sputtering
As we revealed in this paper, proper sputtering power and uniform magnetic eld produce less surface damage to wafers that is helpful to reduce the interface trap density; relatively high refractive index aluminum oxide lm is much more conducive to improve the surface passivation performance; the formation of the SiOxx is detected at the interfacial layer a er postannealing that is vital to achieve good surface passivation by RF magnetron sputtered aluminum oxide lm
Summary
Surface passivation is still one of the most important techniques to improve the performance of low-cost highefficiency industrial solar cells. ere are two different strategies to achieve surface passivation, which are (i) reducing the interface trap density by passivating dangling bonds with, for example, H atomic or a thin dielectric lm like SiOxx, which is commonly referred to as chemical passivation, and (ii) socalled eld-effect passivation that a reduction of minority carrier concentration is obtained by means of a built-in electric eld [1]. Among the multifarious techniques adopted to fabricate aluminum oxide lm, atomic layer deposition (ALD) has turned out to be a technique providing outstanding surface passivation to laboratory high-efficiency solar cells [4, 11]. As the surface passivation of reactive sputtered aluminum oxide lm is mainly limited by high interface traps density while xed negative charge of sputtered lms is similar to that deposited by ALD [7, 9, 10], proper sputtering parameters, proper sputtering power, for instance, can reduce the surface damage caused by highenergy ions bombardment during the process and result in the reduction of interface trap density. Deposition rate (nm/min) 4.862 6.893 8.997 11.256 12.678 14.288 refractive index, and XPS were implemented to characterize the properties of the aluminum oxide lms
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