We have successfully constructed photoelectrochemical (PEC) cells based on the Langmuir-Blodgett (LB) films of poly(3-hexylthiophene) (P3HT) doped with Dy@C-82. The composite structure is featured by the interaction between Dy@C82 and the thiophene building blocks of P3HT, which take an edge-on arrangement at the air/water interface. The usage of the P3HT-Dy@C-82 composite LB, films in photoelectrochemical (PEC) cells yields a dramatic enhancement of the cathodic photocurrent, with the power-conversion efficiency (eta(e)) and quantum yield (Phi) being up to 16-fold and 9-fold higher, respectively, than those of pure P3HT cells. This is attributed to the facile photoinduced electron transfer between P3HT and Dy@C-82, which is also revealed by photoluminescence (PL) spectroscopic characterization. The optimum PEC performance is found to be correlated with an ordered film structure as revealed by AFM measurements. The effects of the electron acceptor, bias voltage, light intensity, and number of layers have been studied in detail. Comparison studies have also been conducted with bilayer PEC cells and PEC cells in which Dy@C-82 is replaced by C-60. A possible mechanism for the cathodic photocurrent generation is proposed on the basis of these studies.