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.