In this paper, an interleaved high-voltage gain DC-DC converter is proposed for use with photovoltaic (PV) systems. By integrating two three-winding coupled inductors (CIs) with switched capacitor (SC) cells, the voltage gain is further extended. Through passive diode-capacitor clamp circuits, the energy stored in the leakage inductances is absorbed; additionally, the voltage stress of the power switches is clamped to a value far lower than the output voltage, which enables designers to select switches with low-voltage ratings. Due to the interleaved structure of the proposed converter, the input current has a small ripple, which leads to the increased lifespan of the PV panels. In addition, the current stress on the components is reduced. Thanks to the leakage inductances of the CIs, the zero current switching (ZCS) condition is intrinsically provided for the diodes; accordingly, the adverse impact of the diodes reverse-recovery is alleviated. The operating principles, steady-state analyses, and design considerations of the proposed converter are presented in this paper. A comparison with other similar converters is carried out to verify the merits of the proposed converter. Finally, the theoretical analyses are confirmed through the experimental results of a 400 W prototype with an output voltage of 400 V.