We demonstrate that the dark current of a multi-quantum well (MQW) solar cell can be reduced significantly if grown by atomic H-assisted molecular beam epitaxy (H-MBE). Atomic H irradiated during MBE growth acts to passivate the defects and smooth heterointerfaces are formed. Further, it is shown that the dark current can be reduced in a modified MQW configuration consisting of two-step QWs as opposed to conventional square-shaped QWs. The suppression of non-radiative recombination at the MQW heterointerfaces, which is achieved by both schemes, is expected to realize improved performance of MQW-based solar cells and photovoltaic devices. (C) 2002 Elsevier Science B.V. All rights reserved.