Strain in perovskite solar cells: origins, impacts and regulation

Abstract

Metal halide perovskite solar cells (PSCs) have seen an extremely rapid rise in power conversion efficiencies in the past few years. However, the commercialization of this class of emerging materials still faces serious challenges, one of which is the instability against external stimuli such as moisture, heat, and irradiation. Much focus has deservedly been placed on understanding the different origins of intrinsic instability and thereby enhancing their stability. Among these, tensile strain in perovskite films is an important source of instability that cannot be overcome using conventionally extrinsic stabilization approaches such as encapsulation. Here we review recent progress in understanding of the origin of strain in perovskites as well as its corresponding characterization methods, and their impacts on the physical properties of perovskites and the performance of PSCs including efficiency and stability. We then summarize the latest advances in strain-regulation strategies that improve the intrinsic stability of perovskites and photovoltaic devices. Finally, we provide a perspective on how to make further progress in stable and high-efficiency PSCs via strain engineering.

Interfacial Strain Engineering in Wide-Bandgap GeS Thin Films for Photovoltaics

“…The α of GeS is calculated to be 3.1 × 10 –5 K –1 by the shift of XRD peaks (Figure f), agreeing well with a previous report (Figure S4). We find that this value is close to that of lead-halide perovskites that possess high α ranging from 3.3 to 8.4 × 10 –5 K –1 due to their soft lattices. − This high α of GeS may be attributed to its layered crystal structure, where the weak van der Waals force between layers leads to the large thermal expansion along the out-of-plane direction. This is a common trend also seen in other widely studied layered materials such as graphite with an α of ∼3.0 × 10 –5 K –1 …”

Strain relaxation and domain enlargementviaphase transition towards efficient CsPbI2Br solar cells

“…If there is a compressive strain in the perovskite film along the out-of-plane direction ( ε y ), the in-plane direction ( ε x ) would be under the tensile strain simultaneously, and vice versa . 38 Moreover, ε x and ε y are linearly related according to Poisson's ratio eqn (3), ε y = − υ ε x where ε y is the compressive strain along the out-of-plane direction, ε x is the tensile strain along the in-plane plane, and υ is Poisson's ratio. Here, we performed in-plane XRD measurements on the pristine and the PTG prepared CsPbI 2 Br films, which measures the spacing of the planes parallel to the substrate (Fig.…”

Defects and stability of perovskite solar cells: a critical analysis

“…112,113 Strain in perovskites can be divided into two types: the local lattice strain, and externally induced strain. 114 The local lattice strain mainly comes from the instability of the perovskite structure and the local lattice mismatch. The externally induced strain in different perovskite solar cells can be very different due to the usage of the different charge transport layers and perovskite compositions with different expansion coefficients.…”