Over 1 μm electron-hole diffusion lengths in CsPbI2Br for high efficient solar cells
All-inorganic cesium lead halide perovskites (CsPbX 3 , X = Cl, I, Br) have attracted great attention for developing high-performance photovoltaics due to their superb thermal stability. However, the short electron-hole diffusion lengths ( L D s) in CsPbI 2 Br perovskite are the primary limiting factor for further improvement of the power conversion efficiencies (PCEs) of the CsPbI 2 Br solar cells. Herein, a simple yet effective method is reported to prolong the L D s in CsPbI 2 Br via codoping of Zn 2+ and acetate (Ac − ) ions (i.e., using Zn(Ac) 2 as dopant). It is demonstrated that Zn 2+ partially replaces Pb 2+ to form a more stable black phase, and Ac − coordinates with Pb 2+ to passivate the defects at the perovskite grain boundaries which reduces electron-hole recombination within the perovskite. As a result, the L D s of Zn(Ac) 2 doped CsPbI 2 Br are greater than 1 μm, which is the first report on all-inorganic perovskites. The champion PCE of the CsPbI 2 Br solar cells is drastically increased from 12.31% to 14.93% upon doping with Zn(Ac) 2 , stemming mainly from the increased open-circuit voltage and fill factor. Furthermore, the non-encapsulated devices with Zn(Ac) 2 doped CsPbI 2 Br show less than 10% efficiency loss after storage in dry air for 30 days.
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