Atomic layer deposition of high-mobility hydrogen-doped zinc oxide

- High mobility (47 cm2/Vs) ZnO:H can be prepared by ALD using H2 plasma treatments.
- A strong enhancement in grain size is induced by the H2 plasma treatment.
- The H2 plasma is able to dope the ZnO:H to the level of 8×1019 cm−3.
- A comparison to conventional In2O3- and ZnO-based TCOs is presented.
- ALD ZnO:H is promising for SHJ-perovskite tandem cells and as rear TCO in silicon SHJ solar cells.

In this work, atomic layer deposition (ALD) has been employed to prepare high-mobility H-doped zinc oxide (ZnO:H) films. Hydrogen doping was achieved by interleaving the ZnO ALD cycles with H2 plasma treatments. It has been shown that doping with H2 plasma offers key advantages over traditional doping by Al and B, and enables a high mobility value up to 47 cm2/Vs and a resistivity of 1.8 mΩcm. By proper choice of a deposition regime where there is a strong competition between film growth and film etching by the H2 plasma treatment, a strongly enhanced grain size and hence increased carrier mobility with respect to undoped ZnO can be obtained. The successful incorporation of a significant amount of H from the H2 plasma has been demonstrated, and insights into the mobility-limiting scatter mechanisms have been obtained from temperature-dependent Hall measurements. A comparison with conventional TCOs has been made in terms of optoelectronic properties, and it has been shown that high-mobility ZnO:H has potential for use in various configurations of silicon heterojunction solar cells and silicon-perovskite tandem cells.