Hi,

Try to use different TiO2 blocking layer (like spin-coated or spray coated). Optimization of the thickness is needed for ALD TiO2. 50 nm is to thick.

regards.

Hi Alec,

Don't be depressed. Device making always come with its share of frustration, because there is only so much people report in their papers. You should first learn how to interpret your IV curve. Here this quasi-linear response seems almost like an ohmic contact (although I recommend you push it further by carrying IV at different temperatures and light intensities to confirm that). That is typically caused by leaks, or pinholes, causing a direct contact between your active material and one of your electrode. Sort of by-passing your electron/hole conducting materials. Excessively thick TiO2 would cause your current to drop, but not your FF.

That would happen if your TiO2 (or X60+LiTFSI+t-BP) is non-uniform. On the slide you show on the photo, how many cells do you make (determined by the number of gold cathodes you design), and what size? As a start you should make sure your TiO2 is pinhole-free, as well as your hole-conducting layer.

Good luck.

Thank you Ludmila Cojocaru , I can also spin coat Titanium tetraisopropoxide to change the blocking layer. I think the problem could be caused by HTM or blocking layer.

Thank you for your encourage and suggestion, Victor Malgras . I am going to work with blocking layer and HTM.

We get blocking layer from ALD system so theoretically it should be pinhole-free? However in the HTM solution there are possible some Li crystal which causes comet effect (HTM solution is not freshly made). I know the FTO has been cleaned and perovskite solution has been filtered, so in the photo the film looks good (color, morphology), right?

It is hard to carry the I-V tests at different temperatures but I made 3 batches of devices all suffer from low Jsc. (One of them has Voc of 1.05 V) So there should be a big series resistance in the devices.

In 3*3 cm2 FTO I have 6 devices with area of 0.12 cm2. The device size is similar with literature.

Thank you again for your help!

You might want to inspect your surface after ALD depostion using SEM (back-scattering mode) to see if you could have pinholes. Alternatively, use that coated FTO as a working electrode in an electrochemical station and run a linear sweep voltammetry in any standard electrolyte. If you have an ohmic (short circuited) response then you have pinholes.

One of the best method to cast dense blocking layer is by spraying titanium diisopropoxide bis(acetylacetonate) on your FTO heated at 400-500° (spray pyrolysis). You can also go for immersing your FTO in a diluted aqueous solution of TiCl4 kept in an oven at 70° for 2h. These methodologies should be available online somewhere.

As you guessed by now, the perovskite layer is the easiest bit of the process :D

Thank you, Victor Malgras, even surprised that perovskite layer is the easiest. I'm going to test HTM and blocking layer individually. Thank you for your help!

Dear I think you solved your problem.

But it is useful to give an answer which may benefit the other researchers.

In order to diagnose your solar cell you must measure also the dark I-V curve in the forward and reverse biasing.

This will show you how massive is your shunting effect of your pinholes that may be metallized and make shortcircuit across the junction. It will also show you how is the series resistance is it linear or nonlinear as well as it high or low. As the open circuit voltage is low, it may point out to the presence of nonlinear ohmic ohmic contacts at the metal semicondcutor interface.

I would like that you see the paper in the link:Article A. Zekry and G. El-Dllal, “ effect of MS contact on the elec...

I think every one making solar cells must read this paper.

One has to be sure that his metal contacts to the interfacing semicondcutor must be ohmic and low such that it does not affect the performance of the solar cells.

If you do not have pinholes than for sure it it is X60+LiTFSI+t-BP/Au contact or X60 contact with the perovskite.

You have to be sure that these materials build good HTL with the perovskite and that it builds good ohmic contact with Au.

You can look at the conditions for good HTL at the paper in the link:Conference Paper Generic Analytical Models for Organic and Perovskite Solar Cells

If these materials are all ready used then it is the processing and heat and annealing are not correct in your case.

You may need some annealing step after the gold deposition.

Best wishes