Band alignment of MAPb(I1 –xBrx)3 thin films by vacuum deposition

In this work, the mixed bromide iodideleadperovskites CH3NH3Pb(I1 –xBrx)3 (0  ≤ x ≤ 0.67) thin films were prepared by co-evaporation of CH3NH3I, PbI2, and PbBr2. The electronic properties of CH3NH3Pb(I1 –xBrx)3 thin films were investigated byX-ray and ultraviolet photoelectron spectroscopyin-situ. The results of core level bindingenergy show that there is nochemical shift of the C1s, N1s, Br3d5, and I3d5 when the Br composition changes, while there is an approximately linearchemical shift of Pb4f7 to higher bindingenergy as the Br composition increases. The density functional theory calculation reveals that there is morecharge transfer fromPb to Br than I, which results in thechemical shift of Pb4f states. On the other hand, thevalence band maximum increases as the Br composition increases, while the work function shows no obvious change, because the conduction band is dominated byPb 6p orbitals while thevalence band is dominated by halidep orbitals. Our work demonstrates the adjustability of theenergy level alignment of MAPb(I1 –xBrx)3 by the Br composition.

Source: Applied Physics Letters - December 8, 2016 Category: Physics Authors: Xianzhong Zhou, Wang Ye, Xiaoli Li, Wei Zheng, Richeng Lin, Feng Huang and Dingyong Zhong Source Type: research