Abstract
Grain boundaries (GBs) as defects in the crystal lattice detrimentally impact the power conversion efficiency (PCE) of polycrystalline solar cells, particularly in recently emerging hybrid perovskites where non-radiative recombination processes lead to significant carrier losses. Here, the beneficial effects of activated vertical GBs are demonstrated by first growing large, vertically-oriented methylammonium lead tri-iodide (CH3NH3PbI3) single-crystalline grains. We show that infiltration of p-type doped 2′-7,7′-tetrakis(N,Ndi-p-methoxyphenylamine)-9,9-spirobifluorene (Spiro-OMeTAD) into CH3NH3PbI3 films along the GBs creates space charge regions to suppress non-radiative recombination and enhance carrier collection efficiency. Solar cells with such activated GBs yielded average PCE of 16.3±0.9%, which are among the best solution-processed perovskite devices. As an important alternative to growing ideal CH3NH3PbI3 single crystal films, which is difficult to achieve for such fast-crystallizing perovskites, activating GBs paves a way to design a new type of bulk heterojunction hybrid perovskite photovoltaics toward theoretical maximum PCE.
