Search for: All records

Abstract The interface between the hole transport layer (HTL) and perovskite in p‐i‐n perovskite solar cells (PSCs) plays a vital role in the device performance and stability. However, the impact of this interface on the vertical phase segregation of mixed halide perovskite remains insufficiently understood. This work systematically investigates the impact of chemical and electronic properties of HTL on vertical halide segregation of mixed‐halide perovskites. This work shows that incorporating a poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA)/CuI_xBr_1‐xbilayer as the HTL significantly suppresses light‐induced vertical phase segregation in MAPb(I_0.7Br_0.3)₃. This work uses grazing‐incidence X‐ray diffraction (GIXRD) to capture the depth‐resolved composition change of MAPb(I_0.7Br_0.3)₃at the interface and within the bulk under illumination. By changing the illumination direction and the electronic properties of HTL, this work elucidates the roles of charge carrier extraction and interfacial defects on vertical phase segregation. The PTAA/CuI_xBr_1‐xbilayer, with its synergistic passivation and efficient hole extraction ability, stabilizes the interface and bulk of the mixed halide perovskite layer and prevents phase segregation. This work underscores that synergetic passivation and efficient hole extraction pack a more powerful punch for arresting the vertical phase segregation in mixed‐halide perovskite. 

Transport properties of doped conjugated polymers (CPs) have been widely analyzed with the Gaussian Disorder Model (GDM) in conjunction with hopping transport between localized states. These models reveal that even in highly doped CPs, a majority of carriers are still localized because dielectric permittivity of CPs is well below that of inorganic materials, making Coulomb interactions between carriers and dopant counter-ions much more pronounced. However, previous studies within the GDM did not consider the role of screening the dielectric interactions by carriers. Here we implement carrier screening in the Debye-H¨uckel formalism in our calculations of dopant-induced energetic disorder, which modifies the Gaussian density of states (DOS). Then we solve the Pauli Master Equation using Miller-Abrahams hopping rates with states from the resulting screened DOS to obtain conductivity and Seebeck coefficient across a broad range of carrier concentrations and compare them to measurements. Our results show that screening has significant impact on the shape of the DOS and consequently on carrier transport, particularly at high doping. We prove that the slope of Seebeck coefficient vs electric conductivity, which was previously thought to be universal, is impacted by screening and decreases for systems with small dopant-carrier separation, explaining our measurements. We also show that thermoelectric power factor is underestimated by a factor of ∼ 10 at higher doping concentrations if screening is neglected. We conclude that carrier screening plays a crucial role in curtailing dopant-induced energetic disorder, particularly at high carrier concentrations.