If you want a bigger back, it's not about moving a weight from point A to point B – it's what happens between those points that counts. Tension is everything. You must know how a rep should feel in order to maximize muscle activation.
But it's really hard to feel each rep when you're using excess momentum, especially in the barbell row. This is called cheating. You throw your back or shoulder toward the bar, creating momentum, then letting the weight "float," bringing your chest toward the weight.
So within the entirety of the rep, your muscles feel the tension for about two inches of it. This not only puts massive amounts of unnecessary stress on the muscle tendons, it's not benefiting you much, either.
Use bands to help you create something called "isotonic muscle action." What does that mean? Constant tension. And for our purposes, constant control. For this you're going to use bands that'll help you pull with the same speed, tension, and control through both phases of the lift (concentric and eccentric).
Start by placing some medium tension bands on the bar that'll give a slight flex (use a bigger band for more weight). Not only will it promote good tempo, but at no point during the rep can you cheat to get past your weak point. Pull it too fast, and the band stretches instead of the weight moving. Once you experience how isotonic reps feel, apply the same control to the traditional lifts.
Using bands like this will work great for bodyweight pulls such as inverted rows and assisted chin-ups. It also works well with pulldowns, seated cable rows, and similar movements.