Dear researchers,

I'm trying to fabricate a NiO layer for HTL of organic solar cells or photodiodes by sol-gel method.

I used nickel acetate tetrahydrate, ethyl alcohol (or 2-methoxyethanol), and ethanolamine which commonly used for NiO sol-gel precursor solution.

(NiAc: 0.1 M, molar ratio of NiAc and ethanolamine = 1:1)

When I put together these three ingredients in a vial and stirred with heating (60~70oC) for 1~3 h, the precursor solution change to the hazed (cloudy).

Especially when I put the ethanolamine in the mixture of NiAc and EtOH, hazing started as it mixed up.

What is the precipitate of the precursor solution? when the precursor solution maintained without stirring for a day, precipitate settled down with green-grayish color.

I think the ideal precursor solution should be a clear and homogeneous state with greenish or blueish color. But my solution is not clear and has precipitates.

Is Ni(NO3)2-based sol-gel method (combustion method) is better? I'm willing to change NiAc to Ni(NO3)2 if the latter is more practical or easy-to-fabricate.

I struggled with this phenomenon.

Could anyone suggest to me a clue about this phenomenon?

Best regards,