[kamiyu]

I am applying for postdoc in Chemistry, with the area of organic electronics (OLEDs, organic photovoltaics etc)

I am thinking what contract time length is more common, 1 year or 2 years?

Is there any difference between Canada and USA in terms of contract length?

[Yggdrasil]

I think in the US, postdoc contracts are typically year-to-year (i.e. one year contracts with the option to renew the contract at the end of the year).  Some institutions will have term limits for postdoc (e.g. at my institution, postdoc contracts can be renewed for a maximum of five years), though usually one can seek exemption to the rule.

[Corribus]

At many Universities in the US once you exceed the maximum allowed for a post-doc, you get automatically converted to research staff or the equivalent (if the PI still wants you around). But this isn't usually a good thing. Post-docs are supposed to be short training experiences to prepare you for a more permanent research position. After three or four years you should definitely be thinking about moving on, or you will completely lose a lot of your marketability, at least for higher academic positions.