Characterization of Interface Properties for Efficient and Stable Perovskite Solar Cells

Abstract

Perovskite solar cells (PeSCs) have attracted significant attention as promising candidates for next-generation thin film photovoltaics. Despite tremendous progress in the power conversion efficiency (PCE) of PeSCs, the long−term stability issue remains a significant challenge for commercialization. In this dissertation, some materials activated interface and additive engineering were developed toward the PeSCs with the aim of improving their stability as well as efficiency, for practical application in ambient environment. Firstly, significant enhancements in the device efficiency and stability are achieved by using a surface−active lead acetate (Pb(OAc)2) at the top or bottom of methylammonium lead triiodide (MAPbI3)−based perovskite. When a saturated Pb(OAc)2 solution is introduced on the top of the MAPbI3 perovskite precursor, the OAc− in Pb(OAc)2 participates in lattice restructuring of MAPbI3 to form MAPbI3−x(OAc)x, thereby producing a high−quality perovskite film with high crystallinity, large grain sizes, and uniform and pinhole−free morphology. Moreover, when Pb(OAc)2 solution is mixed in the poly(3,4−ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solution in the bottom way, the OAc− in Pb(OAc)2 improves the water resistance of PEDOT:PSS. As the OAc− easily bonds with the Pb2+, the deposition of MAPbI3 precursor onto the Pb(OAc)2 mixed with PEDOT:PSS results in a reduction of the uncoordinated Pb, leading to strong stabilization of perovskite layer. Both the top− and bottom− treated devices exhibit enhanced PCE values of 18.91% and 18.15%, respectively, compared to the conventional device with a PCE of 16.25%, which originates from decreased trap sites and reduced energy barriers. In particular, the bottom−treated device exhibits long−term stability, with more than 84% of its initial PCE over 800 h under an ambient environment. Secondly, phenyl ethyl−ammonium iodide (PEAI)−induced bilateral interface engineering was developed to improve the device efficiency and stability of MAPbI3-based PeSCs. Introducing PEAI onto PEDOT:PSS layer modifies the surface properties of the PEDOT:PSS and facilitates the formation of a high−quality perovskite active layer with enlarged grains on the PEDOT:PSS. The PEA+ in the PEAI−PEDOT:PSS also alters the work function of the PEDOT:PSS, leading to a reduction in the energy difference between the PEDOT:PSS and MAPbI3 perovskite layer, which decreases energy loss during charge transfer. Additionally, depositing PEAI onto three dimensional (3D) perovskite yields a two dimensional/three dimensional (2D/3D) stacked structure for the perovskite active layer. Because the 2D top layer acts as a capping layer to prevent water penetration, the stability of the perovskite active layer is significantly enhanced. A PeSC device fabricated based on this combination exhibits enhanced PCE and extended device lifetime compared to a pristine PeSC. Under high−humidity conditions (75 ± 5%), the PEAI-treated PeSC retains 88% of its initial PCE after 100 h. In contrast, a pristine PeSC device loses over 99% of its initial PCE after only 25 h under the same conditions. Lastly, by blending organic halide salts, PEAX (X = I, Br) with MAPbI3, we achieved remarkable enhancements in the water-repellency of perovskite films and long-term stability of PeSCs, together with enhanced PCE. The hydrophobic aromatic PEA+ group in PEAX protects the perovskite film from destruction by water. In addition, the smaller halide Br– in PEABr restructures MAPbI3 to form MAPbI3−xBrx during post-annealing, leading to lattice contraction with beneficial crystallization quality. The perovskite films modified by PEAX exhibited excellent water resistance. When the perovskite films were directly immersed in water, no obvious decompositions were observed, even after 60 s. The PEAX−ecorated PeSCs exhibited considerable long-term stability. Under high−humidity conditions (60±5%), the PEAX−decorated PeSCs held 80.5% for PEAI and 85.2% for PEABr of their original PCE after exposure for 100 h, whereas the pristine PeSC device lost more than 99% of its initial PCE after exposure for 60 h under the same conditions. Moreover, compared to the pristine device with a PCE of 13.28%, the PEAX−decorated PeSCs exhibited enhanced PCEs of 17.33% for the PEAI device and 17.18% for the PEABr device.