I don’t know of any exercise that just focuses in on the chest. Any variation of a bench press or a dip (which are some of the best chest exercises available) are going to involve the triceps and also the deltoids. Even flyes will not completely isolate the chest, because there will be some stabilizing contractions around the elbow joint as well as some front deltoid activation.
Every form of pushup I know of also uses the delts and the triceps. If you want to build your chest I would stick to heavy, compound, pushing exercises for the upper body: bench presses, dips, and pushups. Realize that pushups are not a “heavy” exercise once you build up some strength and can knock them out easily.
You may need to find ways to increase the resistance such as raising your feet or wearing a weighted vest. Just my 2 cents.