Impact of precursor dosing on surface passivation (ALD)

A schematic of the sample measured against effective lifetime ms and excess carrier density (cm-3)

High-efficiency solar cell architectures (including silicon heterojunction (SJH) and perovskite/silicon tandems) rely heavily on the unique properties of transparent conducting oxides (TCOs).  The push towards terawatt-scale PV manufacturing means it is increasingly desirable to develop indium-free TCOs to facilitate the upscaled manufacturing of high-efficiency cell designs.  

Aluminium-doped ZnO (AZO) deposited by atomic layer deposition (ALD) has emerged as a promising candidate due to its combination of optical transparency and electrical conductivity.  In addition, AZO has also been shown to passivate the c-Si surface.

The ability for one material to provide all three properties without requiring any indium is advantageous in single junction and tandem solar devices.  In the paper 'Impact of precursor dosing on the surface passivation of AZO/AIOx stacks formed using atomic layer deposition', published in Energy Advances, the authors* demonstrate exceptional silicon surface passivation.  This was achieved by using AZO/AIOx stacks deposited with ALD, with a Jo<1fA cm-2 and corresponding implied open circuit voltage (iVoc) of 740mV.  

The authors provide a comprehensive analysis of the role of ALD precursor dosing to achieve optimised performance.  A broad range of characterisation approaches were used to probe the structural, compositional and chemical properties of AZO films which indicated that the passivation properties are governed by a delicate interplay between the Zn and AI concentrations in the film, highlighting the importance of precise control.  Optical modelling in a single junction SHJ architecture indicates that these AZO films are close in performance to high-mobility indium-containing TCOs,

The insights provided by this work may help to further the case of indium-free TCOs, which is critical for upscaled production of high-efficiency solar cells.

 

*The team of authors composed of the following, led by Yan Wang of Oxford Materials:

Oxford Materials, University New South Wales and Oxford Physics.