The effect of antisolvent selection and dripping time on CsPbIBr2

Key findings:
- The application of IPA after 10 seconds is a reproducible and simple way of significantly enhancing crystallinity and stability.
- A parabolic relationship was found between XRD intensity and dripping time when IPA is used.
- At least 8 seconds is needed for the solution to spread out.
- Application of other antisolvents (DEE, ClBn and Tl) seems to accelerate degradation and reduce overall quality of the final sample.

Introduction and hypothesis:
Antisolvent quenching has been shown to be a useful method for improving perovskite films. My hypothesis was that both antisolvent selection and the conditions under which it is applied would have a large impact on the final sample. I identified the dripping time a variable which could have a significant impact on sample quality. The dripping time being the time elapsed from the initiation of the spin programme before which the antisolvent is applied. In my method I use one-step spin-coating where the perovskite solution is applied statically.

Methodology:
The perovskite precursors Cesium iodide (CsI) and lead bromide (PbBr2) were purchased from Tokyo Chemical Industry. The solvent/ antisolvents were purchased from Sigma Aldrich and they consisted of dimethyl sulfoxide (DMSO 99.9%), isopropanol (IPA), diethyl ether (DEE), toulene (Tl) and chlorobenzene (ClBn).
The precursor solution consisted of preparing a 1M solution of PbBr2 and IPA in DMSO, which was heated for 90 minutes to completely dissolve the precursors. 50µL of this was then statically spin-coated onto the sample and 100µL of antisolvent was applied after a certain period (dripping time). The samples were spin-coated at 4000RPM for 50 seconds. The annealing was carried out at 50 °C for 5 minutes followed by slowly increasing the temperature to 250°C and kept at this temperature for 5 minutes.
This experiment was carried out in three phases. In the first part I studied the effect of different antisolvents on the measurable properties of CsPbIBr2 while the dripping time was kept constant at 8 seconds. In the second stage I varied the dripping time of the best sample IPA from 5 seconds up to 20 seconds, in steps of 5 seconds. In the final part of the investigation, I measured the samples from the first two parts again, 5 weeks after they had been stored in the laboratory (at 23°C and RH=20%).