3 Results and discussion
3.1 Effect of hydrogen concentration on the IHfO:H thin films
Hydrogen doping has been proved to be an effective strategy to modify
the performance of the TCO films, such as reducing the square resistance
and improving the mobility, by influencing the crystallinity, forming
shallow donor states, and passivating the structural
defects.25-27 We investigated the effects of hydrogen
doping on the IHfO:H films by varying the H2concentrations (gas flow ratio of hydrogen to argon: 0 %, 0.5 %, 0.8
%, 1.2 % and 1.5 %) during the deposition process. Referring to the
fabrication process of traditional SHJ solar cells, the series of IHfO:H
films were all annealed at 200 °C in air for 20 minutes.
Figure 2 shows the XRD patterns of the IHfO:H films with different
hydrogen concentrations after annealing at 200 °C. According to the
standard comparison card (JCPDS No.06-0416), the diffraction peaks of
(211), (222), (332), and (444) belonging to the cubic bixbyite
polycrystalline structure of In2O3 are
observed. The absence of diffraction peaks for HfO2indicates that substitutional doping (Hf4+ replacing
In3+) forms a solid solution in which
HfO2 was dissolved into the
In2O3 lattice during the film growth
process.28 The intensity of the diffraction peak (222)
in all samples is much higher than that of the other peaks, which
indicates that (222) is the preferential crystallization direction. We
calculated the average grain size D of the IHfO:H films corresponding to
the full width at half maximum (FWHM) of the (222) diffraction peak
according to the Scherrer formula,19 as included in
Figure 2.
It can be seen that the average grain sizes of all the samples are in
the range of 50±5 nm, which implies that the H2concentration hardly affects the crystallinity of the films. Annealing
can greatly improve the crystallinity of the IHfO:H films, thus
weakening the effect of hydrogen doping on the crystallinity of the
films, as will be discussed below.