We characterized the electrical behavior of crystalline silicon (c-Si) and Cu(In(1-x)Ga(x))Se2 (CIGS) solar cells by current-voltage (I-V) and capacitance-voltage (C-V) methods. We investigated the temperature-dependent carrier transport mechanism by determining the parameters of ideality factor (n) and activation energy (E(a)) deduced from I-V measurements. CLGS solar cells, as a function of temperature, showed drastic changes in n and E(a) in the space charge region (SCR) that forms near the ZnS/CIGS interface. Furthermore, by using a C-V measured substrate doping profiling method, we confirmed that the CIGS absorption layer had a graded band-gap structure from the end point of the SCR to the CIGS/Mo back contacts, while c-Si solar cells had a uniformly doped carrier concentration.