Halide Perovskites: Is It All about the Interfaces?

Abstract

Design and modification of interfaces, always a critical issue for semiconductor devices, has become a primary tool to harness the full potential of halide perovskite (HaP)-based optoelectronics, including photovoltaics and light-emitting diodes. In particular, the outstanding improvements in HaP solar cell performance and stability can be primarily ascribed to a careful choice of the interfacial layout in the layer stack. In this review, we describe the unique challenges and opportunities of these approaches (section 1). For this purpose, we first elucidate the basic physical and chemical properties of the exposed HaP thin film and crystal surfaces, including topics such as surface termination, surface reactivity, and electronic structure (section 2). This is followed by discussing experimental results on the energetic alignment processes at the interfaces between the HaP and transport and buffer layers. This section includes understandings reached as well as commonly proposed and applied models, especially the often-questionable validity of vacuum level alignment, the importance of interface dipoles, and band bending as the result of interface formation (section 3). We follow this by elaborating on the impact of the interface formation on device performance, considering effects such as chemical reactions and surface passivation on interface energetics and stability. On the basis of these concepts, we propose a roadmap for the next steps in interfacial design for HaP semiconductors (section 4), emphasizing the importance of achieving control over the interface energetics and chemistry (i.e., reactivity) to allow predictive power for tailored interface optimization.

Unveiling the Nanoparticle‐Seeded Catalytic Nucleation Kinetics of Perovskite Solar Cells by Time‐Resolved GIXS

“…The PbS NC‐seeded perovskite thin film exhibited enhanced crystallinity, crystal orientation, and thermal stability, together with the refined film morphology of reduced pinholes and grain boundaries, compared to the pristine thin film. All the elucidated effects of the PbS nanocrystals provide hints for the future design on seeding growth of perovskite thin films or a heterointerface‐enhanced performance of halide perovskite solar cells, by taking into account the crystal lattice matching and ligand surfaces of the nanocrystals.…”

High voltage vacuum-processed perovskite solar cells with organic semiconducting interlayers

“…30 Non-radiative recombination in the perovskite layer can be regulated through controlled lm crystallization/ processing, while interface recombination should be minimized through the choice of suitable transport materials and optimized device architectures. 31 The inuence of interlayer chemical and electronic properties on transport and recombination in vacuum-deposited perovskite solar cells has not been fully investigated, although it is critical to modulate and maximize FF, V oc and stability. Here we studied the inuence of interlayers and cathode work function at the C 60 interface in vacuum-deposited p-i-n perovskite solar cells.…”

Thermal stability of mobility in methylammonium lead iodide

“…While valuable, the implicit encapsulation provided by electrical contacts and hole-/electron-blocking layers in devices obscures information on the stability of the material itself. Additionally, the electronic properties of interfaces between MHPs and transport layers may not necessarily be representative of the material itself [29].…”

“…Because the technique does not require electrical contacts or transport layers, it can be carried out on isolated thin films, discontinuous films or even powders. The absence of physical contacts removes contributions from external interfaces [29,33,34], and enables us to make unambiguous statements on the thermal stability of the compound itself. For MHPs such as MAPbI 3 the exciton binding energy is known to be very small [35], and we can approximate f » 1.…”