A high-efficiency inverted bulk heterojunction (BHJ) solar cell with good air stability is fabricated using annealing-free ZnO nanocrystals as an electron-transport layer and a blend of a low bandgap polymer PDTSTPD and PC(71)BM as an active layer. A power conversion efficiency as high as 6.7% has been achieved on the inverted devices with an active area of 1.0 cm(2) using nitrobenzene as a processing additive. The device is highly stable, retaining 85% of its original efficiency after being stored in air for 32 days even without encapsulation. (C) 2011 Elsevier B.V. All rights reserved.