Strain Engineering of Metal–Halide Perovskites toward Efficient Photovoltaics: Advances and Perspectives

Abstract

Due to the impressive optoelectronic properties, metal–halide perovskites (MHPs) have drawn much attention in the field of next‐generation photovoltaics, and perovskite solar cells (PSCs) based on MHPs as light absorbers have reached a certified power conversion efficiency (PCE) of 25.5% in 2020. Despite the great progress, it is still challenging to fabricate high‐quality MHP films. Due to the “soft” ionic nature of MHPs, their polycrystalline films suffer from inevitable residual strain, which is found to not only be fatal to photovoltaic performance of PSCs, but also seriously accelerate the degradation of MHP film. As a result, understanding of strain in MHPs and the key role of strain engineering in improving the photovoltaic performance of PSCs have recently been extensively investigated. Herein, the recent progress of strain engineering in MHPs and their PSCs is systematically summarized. First, the origin of strain in MHPs and the impact of strain on the optoelectronic characteristics of MHPs are carefully discussed. Thereafter, the up‐to‐date studies focusing on strain engineering in PSCs are comprehensively reviewed. At last, the current challenges and future prospects in this field are highlighted.

Crystallization Dynamics of Sn‐Based Perovskite Thin Films: Toward Efficient and Stable Photovoltaic Devices

“…Also, the uncontrollable crystallization of perovskite crystal will induce residual strains in the resultant perovskite film to have negative impact on the optoelectronic properties and stability of the film. [29,30] As expected, deeper understanding on the crystallization dynamics of solution-processing perovskite film and characteristics of Sn-based perovskites are of great significance toward achieving efficient Sn-based PSCs. So far, there are many comprehensive reviews in this field focusing on the current development and future perspective of Sn-based perovskite in terms of preparation, stability, and efficiency of their PSCs.…”

Managing Defects Density and Interfacial Strain via Underlayer Engineering for Inverted CsPbI2Br Perovskite Solar Cells with All‐Layer Dopant‐Free

“…On the other hand, strain issue remains as another challenge for inorganic PeSCs, which includes intrinsic lattice strain and extrinsically induced strain. [26] Particularly, the latter is mainly induced by thermal expansion mismatch between the perovskite film with high thermal expansion coefficient (α TE : ≈10 −4 K −1 ) and the underlayer with much lower α TE , such as above-mentioned TiO 2 , SnO 2 , or NiO x with α TE of 0.1 ∼ 2 × 10 −5 K −1 . [27][28][29] In addition, the large temperature gradient (△T) from perovskite formation temperature (i.e., >160 °C for CsPbI 2 Br) to room temperature aggravates such mismatch.…”

Multistrategy Toward Highly Efficient and Stable CsPbI2Br Perovskite Solar Cells Based on Dopant‐Free Poly(3‐Hexylthiophene)

“…It has been reported that stress accumulation could induce lattice distortion, reduce the bond strength between atoms and the formation energy of defects. [ 51 ] As a result, it led to more point defects and dislocations, which was not conducive to the migration of free charge carriers. [ 51 ] In addition, stress might promote the phase separation of the mixed halides perovskite.…”

“…[51] As a result, it led to more point defects and dislocations, which was not conducive to the migration of free charge carriers. [51] In addition, stress might promote the phase separation of the mixed halides perovskite. [4,52] These adverse impacts will in turn contribute to the accumulation of strain, forming a vicious circle.…”

“…[4,52] These adverse impacts will in turn contribute to the accumulation of strain, forming a vicious circle. [51] Therefore, less defects and higher stability of CsPbI 2 Br film could be expected with introduction of ThMAAc additive and BTCIC-4Cl interlayer.…”