We carry out the structural design of photonic crystals (PCs) using sensitivity analysis for enhancing optical absorption of thin film microcrystalline silicon (μc-Si) solar cells. In this paper, we employ a model which includes absorption of not only the thin film μc-Si, but also the transparent conductive oxide and metal back reflector for design accuracy. We carry out structural design for this model using sensitivity analysis which maximizes optical absorption in μc-Si layer. As a result, we succeed in obtaining the maximum short circuit current density of 25.2 mA/cm2 for thin film (600-nm thick) μc-Si solar cells (1.4-fold increase compared to the case without a PC).