1) There's a special "sustainability" category on AngelList if you consider jobs in startups. IT jobs can be found there as well as non-IT. What's really nice is that you can figure out a company's mission simply by looking at its short description, eg:
The climate impact of everything made accessible to everyone.
The digital sourcing platform - faster, leaner and more responsible supply chains
2) As for B Corp mentioned earlier, they even provide job listings on a separate website. IT jobs are listed there as well as non-IT, but filters make it easier to find what you need.
3) You might also consider browsing indexes of ethical and sustainable alternatives and manually checking "career" webpages of those companies which attract your attention. Such indexes are the following: ethical, ethical consumer (especially their "technology" category), rank a brand ("telecom", "online", "electronics" categories, although many companies are not ranked yet).
4) UPD: I recently discovered Climate.Careers - a specialized job discovery platform connecting climate-impactful companies with mission-driven talent. You can filter jobs:
- by impact areas (e.g. ecosystems & biodiversity, food & agriculture),
- more specific by climate solutions (e.g. afforestation, vertical farming),
- by role (ICT-related Engineering: Software, Data Analyst, Data Scientist, Design, Quality Assurance, Project Manager and so on);
- and more parameters.
There's quite a lot of job opportunities listed there, including well-known companies such as Ecosia, Too Good To Go, Leap, but not limited to.