Influence of the Electron Selective Contact on the Interfacial Recombination in Fresh and Aged Perovskite Solar Cells

Round 1

Reviewer 1 Report

This manuscript evaluated the influence of the different interfacial recombination in fresh and aged perovskite solar cells. Aged devices showed slower recombination 19 kinetics in comparison to their fresh counterparts, revealing a positive effect of the aging process. The ion migration kinetics are directly related to the perovskite composition. Therefore, this manuscript would be suitable for publication after minor revisions. Detailed comments are as follows:

1. Perovskite composition plays an important role in the dynamics of ionic and charge recombination. This is an obvious result, the authors need to compare the difference between the MAPbI3 device and CsFAMAPbIBr devices, and give some more scientific point.
2. Aged devices showed slower recombination kinetics compared to their fresh devices, revealing a positive effect of the aging process. This recombination is at the interface or the charge recombination inside perovskite?

Author Response

1. Perovskite composition plays an important role in the dynamics of ionic and charge recombination. This is an obvious result, the authors need to compare the difference between the MAPbI3 device and CsFAMAPbIBr devices, and give some more scientific point.

In our manuscript, we have dedicated the whole section 3.2 to the differences between the perovskite composition, between MAPbI3 and CsFAMAPbIBr, starting from the differences in the JV curves and followed by the analysis in the carrier recombination kinetics. In addition, we indicate through the manuscript the fact of having more iodine or bromide in the perovskite composition and how this effects to the carrier dynamics. However, we have added a last sentence in the conclusions to make it clearer:

“This clearly shows that perovskite composition plays an important role in the dynamics of ionic and charge recombination, with MAPbI₃ having a greater ionic accumulation compared to CsFAMAPbIBr that leads to faster carrier recombination, and, consequently, worse device performances.”

1. Aged devices showed slower recombination kinetics compared to their fresh devices, revealing a positive effect of the aging process. This recombination is at the interface or the charge recombination inside perovskite?

We can determine the beneficial effect of aging over carrier recombination, but with TPV it is not possible to discern whether the recombination is happening in the bulk or at the interfaces. What we have made sure is that we avoid the influence of the capacitive component by comparing the kinetics at high carrier densities.

Reviewer 2 Report

The authors compare here the photovoltaic performance of n-i-p perovskite solar cells of various electron extraction layers with or without aging. The results are really interesting and deserve to be published after the authors adress te following issues: 

1. You state that upon ageing, the better extraction of charges is due to improved spiro oxidation and that recombination is reduced due to trap passivation. How do you confirm these two processes (spiro oxidation and trap passivation)?
2. What is this 28 days ageing? I guess this is only indicative, right? Please provide a short explanation. 
3. Additionally, the ageing conditions which contain water (even though the relative humidity is lower than 10%), oxygen and no light should be explained. 

Author Response

1. You state that upon ageing, the better extraction of charges is due to improved spiro oxidation and that recombination is reduced due to trap passivation. How do you confirm these two processes (spiro oxidation and trap passivation)?

We base our conclusions on previous works by our group and others. Despite the use of dopants in spiro, it needs to be further oxidized to improve its properties. This behavior has been already reported in previous publications on perovskites (Cho et al., ACS Energy Lett. 2021, 6, 925−933). This process might happen on the early days of ageing, and it should occur independently of the perovskite composition, both for MAPbI3 and CsFAMAPbIBr. It can be correlated to higher FF and Voc of our devices (Differences in the devices measured on day 1 and day 4, Figures S1 and S5 in the manuscript) which indicate better charge extraction and reduced carrier recombination. For the passivating effect we refer to some previous literature suggests that the O2 molecule might occupy some defects in the perovskite lattice and again we correlate this behavior with the enhancement of Voc over time, observable in Figure S1. Trap assisted carrier recombination is one of the major sources of carrier losses in perovskite solar cells, and it is correlated with Voc losses, therefore the passivating effects are confirmed with the greater Voc values observed after the devices are stored in the dark. Not only that, by passivating defects in the perovskite lattice, the channels that are available for ionic motion are also reduced, so, we reduce ionic motion. We have correlated this behavior with the Voc stability, in which faster times to reach the maximum Voc were correlated to faster ionic reorganization times, as well as with the disappearance of the negative spike in the transient of the transient photovoltage technique.

1. What is this 28 days ageing? I guess this is only indicative, right? Please provide a short explanation. 

We acknowledged the reviewer for this comment. We have modified the section in the experimental part giving more details about the ageing process. As the reviewer suggests, yes, the 28 days is indicative, it is the time that our devices required until the hysteresis was negligible using the same JV scan conditions.

Aging process: Devices were stored in the dark under dry conditions (< 10% H2O, obtained via a synthetic airflow) for up to 6 weeks. The devices were fully characterized during this period to determine the effects of aging on the different device configurations.

1. Additionally, the ageing conditions which contain water (even though the relative humidity is lower than 10%), oxygen and no light should be explained. 

As we have pointed out in the previous comment, we have added a dedicated section to explain how the ageing process was done.