Towards the implementation of atomic layer deposited In2O3:H in silicon heterojunction solar cells

- In2O3:H prepared by ALD exhibits superior optoelectronic properties.
- The nucleation of In2O3:H on a-Si:H is inhibited due to bonded surface hydrogen.
- We propose a mild plasma pretreatment to make the a-Si:H surface reactive prior to ALD.
- Detrimental radiation effects by plasma pretreatment can be annihilated by annealing.
- Silicon heterojunction solar cells with In2O3:H shows a high Jsc of 40.1 mA/cm2.

Hydrogen doped indium oxide (In2O3:H) with excellent optoelectronic properties, deposited using atomic layer deposition (ALD), has been made applicable as a window electrode material for silicon heterojunction (SHJ) solar cells. It is particularly challenging to integrate ALD In2O3:H into SHJ solar cells due to a low reactivity of the metalorganic precursor cyclopentadienyl indium (InCp) with the H-terminated surface of a-Si:H. This challenge has been overcome by a simple and effective plasma-based surface pretreatment developed in this work. A remote inductively coupled O2 or Ar plasma has been used to modify the surface of a-Si:H, thereby promoting the adsorption of InCp on the surface. The impact of the short plasma exposure on c-Si/a-Si:H interface passivation has also been studied. It has been found that the observed degradation of the interface is not due to ion bombardment, but rather due to ultraviolet emission from the plasma. Fortunately, these light-induced defects have been found to be metastable, and the interface passivation can thus easily be fully recovered by a short post-annealing. Using such a mild Ar plasma pretreatment, ALD In2O3:H has been successfully implemented in a SHJ solar cell. A short-circuit current density of 40.1 mA/cm2, determined from external quantum efficiency, is demonstrated for a textured SHJ solar cell with an In2O3:H window electrode, compared to 38.5 mA/cm2 for a reference cell that has the conventional Sn-doped indium oxide (In2O3:Sn, ITO) window electrode. The enhanced photocurrent stems from a reduced parasitic absorption of In2O3:H in the entire wavelength range of 400-1200 nm.

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