Besides other factors, Rf value is dependent on the polarity of the solvent system. It increases with the rise in polarity while showing decreasing trend with the lowering of the polarity of the solvent system. As the solvent system moves over the surface of the stationary phase, it transports the analytes over the particles of the stationary phase.
If a highly polar solvent is used, it will interact strongly with the molecules of stationary phase and will leave only few sites on the surface of stationary phase, free to bind with the analytes. The analytes will therefore move quickly over the stationary phase.
Similarly, polar groups in the solvent can interact strongly with polar functionality in the analytes and prevent interaction of the analytes with the surface of the stationary phase.