Reducing Recombination in Halide Perovskite Solar Cells via Interface Engineering

Abstract

Halide perovskite solar cells have attracted tremendous attention and have been extensively studied over the last decade. Though the power conversion eciency of single junction of perovskite solar cells has reached 26.1%, it still lags behind the theoretical limit, which is largely due to the open-circuit voltage deficit that results from nonradiative recombination in the bulk of perovskite films and also at the interfaces between perovskite and transport layers. When transport layers contact with perovskite, it generally induces new nonradia- tive loss pathways at the interface, resulting in a decrease in device performance. In this dissertation, we engineer the interface of perovskite solar cells to minimize the nonradiative recombination loss via interlayer engineering, electronic decoupling, and surface field, to further enhance perovskite solar cells performance.First, we investigate a photo-crosslinkable naphthalene diimide polymer as the electron- transport layer for n-i-p perovskite solar cells. Inorganic metal oxides such as titanium dioxide (TiO2) and tin oxide (SnO2) have been widely used as the electron-transport layer in n-i-p perovskite solar cell. Nevertheless, these inorganic materials require high annealing temperature and may incur instability of the perovskite layer due to photoactivity. Organic polymers as electron-transport layers offer a new pathway for perovskite solar cells because of their low processing cost, good chemical and thermal stability, and ability to tune the energy levels. Thus, we study the thermal stability, conductivity with and without doping and solvent resistance of naphthalene diimide polymer. Furthermore, we incorporate the photo- crosslinkable naphthalene diimide polymer into perovskite solar cell as electron transport layer, studying the impact of this photo-crosslinkable polymer on device performance. We further explore the influence of this polymer on the structure and optoelectronic properties of perovskite film. Next, we focus on studying the surface/interface passivation of perovskite layer in p- i-n perovskite solar cells. Halide perovskite is polycrystalline material which has many grain boundaries. These grain boundaries as well as perovskite top surface are most defective due to abruptly broken atomic lattice and unsatisfied dangling bonds at a surface/interface, which results in enhanced electron-hole nonradiative recombination. We demonstrate reduced surface recombination velocity (SRV) and enhanced power-conversion eciency (PCE) in mixed-cation mixed-halide perovskite solar cells by using a surface pas- sivator called (3-aminopropyl)trimethoxysilane (APTMS). We show the APTMS serves to passivate defects at the perovskite surface, while also decoupling the perovskite from detrimental interactions at the C60 interface. Lastly, we design two ionic pair salts as interlayers and apply them in between wide bandgap perovskite and C60 layer. Wide-bandgap perovskite can be integrated in the perovskite/silicon tandems to overcome the theoretical limit of single junction solar cells. However, the substantial nonradiative interfacial recombination at the perovskite/C60 interface, limiting open-circuit voltage VOC and thus PCE. We show that benzylammonium tosylate (BzAOTs) and benzylammonium triflate (BzAOTf) interlayers reduced interfacial nonra- diative recombination at the perovskite/C60 interface and enhanced VOC in mixed-halide mixed-cation wide-bandgap (1.7 eV) perovskite solar cells. We unveil that The BzAOTs interlayer improves the device performance through reducing the interfacial nonradiative recombination via surface field while BzAOTf decouples the perovskite film from the detrimental interactions at C60 interface. Our research highlights that engineering interface in perovskite solar cell is an effective approach to reduce recombination in perovskite solar cell, which provides valuable insights for device optimization.