Tartar & Gingivitis
Like humans, Persians can accumulate tartar on their teeth. Additionally, they can certainly develop gingivitis. Proper dental care is a good habit to start when your cat is at a young age. Talk to your vet about scheduling a regular teeth cleaning. You can also clean your cat's teeth in between vet visits. A good place to look for dental care products is Revival Animal Health.
Bad breath can be a sign of nothing more than very dirty teeth, in which case he needs a dental, followed by home care (such as brushing and appropriate diet) by yourself. The veterinarian can demonstrate how to brush his teeth and provide you with safe toothpaste made just for cats.
NEVER use human toothpaste on animals, as it can make them very sick.
If he has really bad breath, you need to first have him checked by a veterinarian to see what is causing it. Bad breath can be a symptom of other health problems, such as liver or kidney disease.