Build a bigger back without weights – 17 exercises and a 20-minute workout to get you started

Your own bodyweight provides plenty of resistance for building bigger lats, stronger traps and a thicker upper back ...
Men's Health

The Old-School Gironda Pull-Up Builds More Back Muscle with Just Bodyweight – Your 4-Step Guide

There's a fairly obvious way to make pull-ups harder once you've become proficient at hauling your own bodyweight over a bar: add more weight. And there's certainly nothing wrong with that approach.