I am a developer and i want to start a startup developing AI applications.Do i need to find a co-founder or should i just do it on my own ?
The answer is "it depends." Most people don't have and don't need a co-founder. A co-founder needs to be someone who is equally excited, interested, talented, and available to work on the same vision you have. The important thing is that you share the same vision (the picture of what the experience is for an ideal customer, both internal customer and external customer, with your product/service). A co-founder should supplement your skills, not so much overlap them.
Business is always simpler when there is only one decision-maker. Employees are a very good substitute for a co-founder when the only reason you want a co-founder is that you don't know how to do something. As a business owner, you will always need advice and support, but it doesn't have to be from another owner. It can be from an advisor, an employee, or a colleague.
My advice is always to start by trying it on your own. When through the process of discovery and research you determine that it would actually be beneficial to share your enterprise with another person, then you can search for a co-founder. But otherwise don't think of a co-founder as a way to get some "free" labor, because it's not.
Your broad idea doesn't reveal nearly enough about you to make an assessment. You could develop AI applications for someone else. You could be a consultant. You could design AI application ideas that you sell to other companies that want to build them. I don't know what's right for you.
Yes. You will need a co-founder who can sell, if this is not something you can do very well on your own.