Video: How Humidity Affects Air-Processed Perovskite Films
Processing in an environment with a humidity of 30-40% rh results in films having a bright yellow colour post spin coating. Placing these films on a 90°C hotplate initially maintains this film colour and after 90-120 minutes, a perovskite film will be formed with a dark brown/grey colour.
If, instead, the humidity of the environment is too high (>40% rh), then the film colour will appear orange/brown after the 30 second spin coating stage. Although the film will revert back to a bright yellow upon placing on a 90°C hotplate and appear a dark brown/grey after the thermal heating stage, the films will provide poor device performance.
Hello, I’m Darren Watters, and I’m a research scientist at Ossila and we’re the team who developed perovskite ink I101.
I’m going to show you some of the techniques we have developed here at Ossila to achieve high efficiency devices based on our ink.
To achieve this, we are in a closed lab using a dehumidifier to reduce the humidity down to about 30%. On our monitor, the humidity is just under 33%.
I want to show you a quick experiment spinning some of our in on a PEDOT:PSS coated substrate. After that, I’ll increase the humidity of the lab and show you how the films differ.
So here we have our PEDOT:PSS coated ITO substrates being annealed at 90 degrees Celsius. We also have our ink at 70 degrees Celsius. What I’m going to do is take my substrate, place it in the Spin Coater and spin it at 3000 RPM.
Now I’m going to take 30 micro litres of our ink and dispense it while it’s still spinning. You want to get close to the substrate but don’t touch it with the pipette. So after just 20 seconds, the film has already turned yellow. In a dry environment, after 30 seconds, your film should still appear yellow.
We’re now going to place this substrate back on the 90 degrees Celsius hotplate. This will then be annealed for 90-120 minutes and it will then turn a dark brown/grey colour.
I’m now going to turn off the dehumidifier and increase the humidity in the lab. We’re now going to wait about half and hour, repeat the experiment, and see what happens.
Welcome back, the humidity of the room has increased to about 60%. We’re not going to spin a film like before and see how it is different.
So now after about 20 seconds, we can see that the film is a brown/grey colour – which is very different from what we saw previously. After 30 seconds, it looks pretty similar as it did at the 20 second point.
As you can see, after a couple of minutes, the films look very similar. But from what we have found, films spun in a high humidity environment don’t work well. I hope this tutorial has been helpful, good luck with your devices.