Conclusion
In conclusion, the effect of post-metallization annealing on solar cells
with SiO2/ZnTiO3/Al as
electron-selective contacts has been systematically studied. Compared to
other well-known dopant-free contacts, ZnTiO3-based
contacts have the best thermal stability and maintain very low contact
resistivities over the annealing temperature range of 25-350 °C. EQE
spectra, PL mapping and effective minority carrier lifetimes
characterization reveal that the passivation effect of
ZnTiO3-based contacts is greatly improved by
post-metallization annealing, which is attributed to the combined action
of SiO2, ZnTiO3 and Al. The
SiO2 layer becomes more uniform and continuous, leading
to the enhanced chemical passivation. In the meanwhile, more Al diffuses
into the ZnTiO3 layer to dope the film, and thus results
in lower WF , which causes enhanced field-effect passivation and
improved electron selectivity. Consequently, the PCE of the
ZnTiO3/c-Si heterojunction solar cells increase
remarkably with increasing post-annealing temperature (when ≤300 °C). By
annealed at 300 °C for 30 min, the champion ZnTiO3/c-Si
heterojunction solar cell possesses a PCE of 22.0%, which is much
higher than its initial PCE (18.5%) before post-annealing treatment due
to the significantly increased V OC andJ SC. Note that compared to other high-performance
solar cells with dopant-free contacts, intrinsic a-Si:H passivation
layer is thoroughly removed in the study, meaning that the high PCE can
be obtained without capital intensive equipment such as PECVD. Our work
demonstrates that perovskite can be a promising candidate for c-Si solar
cells as dopant-free carrier-selective contacts, constructing a
high-performance and low-cost heterojunction solar cell.