This information is missing some statement. Not only reverse bias region affected but also forward bias region strongly affected by light generated photocurrent. There are a lots of source about this topic. Well one of the most important book is" Fundamentals of Solar Cells: Photovoltaic Solar Energy Conversion" by Alan L. Fahrenbruch and Richard H. Bube. I strongly recomend you to play and read this simulation URL (http://pveducation.org/pvcdrom/solar-cell-operation/iv-curve) link to better learn to exact reason of your question mark which is rissing in your mind