I planned to do a solar tracker for my project and I am going to make a RTC solar tracker(actually still considering). So, do I still need photosensor like LDR for tracking the sun?
Do not put a photosensor or sun-finder on your array. Your real-time clock may use the astronomy algorithms provided by Sandia National Lab to be very certain about where the sun is at any given time. (See link below)
Please install a GPS, however, so that your time will be accurate as well as your exact location on the Earth's surface.
Find out how much performance your solar panels lose when they're off by a few degrees--- allowing some error could save motor energy.
Also, check shading row-to-row. If there's shading, your perfect sun-tracking won't actually be helping during sunrise and sunset.
People building solar trackers are common, as a financial gain : not really, but as a project fun : great if you are the tinkering type.
Two examples below, and the one I hoped to find used two small (3 inch sq) pv panels with a jar of water as a lens to drive a small motor in either direction...