Zhaojie Zhang1,Julia Martin2,Ronald Grimm2,Dhandapani Venkataraman1
University of Massachusetts--Amherst1,Worcester Polytechnic Institute2
Zhaojie Zhang1,Julia Martin2,Ronald Grimm2,Dhandapani Venkataraman1
University of Massachusetts--Amherst1,Worcester Polytechnic Institute2
In p-i-n perovskite solar cells (PSCs), the buried hole transport layer (HTL)/perovskite interface plays a vital role in dictating the performance and stability of the full photovoltaic device. However, the impact of HTLs on vertical phase segregation remains unknown. This work systematically explores the impact of electronic and chemical properties of HTLs on vertical halide segregation of mixed-halide perovskite materials. Here, we demonstrate that PTAA/CuI<sub>x</sub>Br<sub>1-x</sub> bilayer HTL significantly suppresses light-induced vertical phase segregation of MAPb(I<sub>0.7</sub>Br<sub>0.3</sub>)<sub>3</sub>. We used grazing-incidence X-ray diffraction (GI-XRD) to capture the depth-resolved composition change of MAPb(I<sub>0.7</sub>Br<sub>0.3</sub>)<sub>3</sub> at the interface and bulk with different HTLs under illumination. Electronic properties including hole density, hole mobility, and energy levels of CuI<sub>x</sub>Br<sub>1-x</sub> were systematically characterized to reveal the impact of HTL on phase segregation. By manipulating the illumination and electronic properties of HTL, we illustrate the interplay between illumination direction, interfacial defects, charge carrier extraction, and vertical phase segregation. Our findings demonstrate that the PTAA/CuI<sub>x</sub>Br<sub>1-x</sub> bilayer, with its synergistic passivation and efficient hole extraction ability, stabilizes the interface and bulk of the mixed halide perovskite layer, preventing phase segregation and possible amorphization. This work highlights that synergetic passivation and efficient hole extraction pack a more powerful punch for suppressing the vertical phase segregation in mixed-halide perovskite.