One paper, which has applied 2D layered perovskite as moisture-resistant light absorber, attracts my interest.

http://onlinelibrary.wiley.com/doi/10.1002/ange.201406466/full  A Layered Hybrid Perovskite Solar-Cell Absorber with Enhanced Moisture Stability

This reminds me of another important paper in this field, the science paper from H. Han's group.http://www.sciencemag.org/content/345/6194/295.abstract  A hole-conductor–free, fully printable mesoscopic perovskite solar cell with high stability

In that paper, it was claimed that a (AVA)x(MA)1-xPbI3 mixed cation halide perovskite was synthesized and exhibits long-term stability. From the XRD, one of the possible assumption is the "mixed cation halide perovskite" is actually a mixture of a 3D MAPbI3 perovskite and a 2D layered AVA2PbI6 perovskite.(AVA and MA exhibits too large size difference to be alloyed). The AVA2PbI6 perovskite inside could be one of the big factor affording better water resistance. Like the paper above.

Incorparating 2D perovskite into the the efficiency-booster perovskite MAPbI3 might be a effective appoarch for more stable cell. Fortunately, the template-directing capablity of such 2D perovskite might lead to better growth of overal perovskite layer,let alone that some of the wide-bandgap 2D perovskite could be used as effective passivation layer as well. Therefore, the stablity issue might be overcome without sacrificing the efficency through this stragery.