High‐Performance Inverted Perovskite Solar Cells with Operational Stability via n‐Type Small Molecule Additive‐Assisted Defect Passivation

Abstract

exceeds 25% for the conventional structure. [5] The inverted structured PSCs also show great promises with advantages such as low-temperature processability and ionic dopant-free hole transport layer, which can contribute toward fabricating flexible devices or improving the operational stability. [6-14] Recently, Zheng et al. reported stable inverted PSCs exhibiting a PCE of 23.0%. [15] Meng et al. demonstrated a highly flexible inverted PSCs with a PCE of 19.9%. [16] Despite such rapid progresses in PSCs, the stability of perovskite still remains below commercialization standards, because perovskite is inherently unstable under ambient environmental conditions such as ultraviolet (UV) irradiation, and is particularly degraded by humidity and heat. Perovskite is hydrophilic, meaning that moistures can readily infiltrate along the grain boundaries of its crystals, triggering severe decomposition of the constituent elements and a consequent decline in device performance. [17,18] In addition, the constituent atomic species of perovskite materials are thermally decomposed at elevated temperatures, even under protective encapsulation layers. The decomposed organic and halide ions preferentially migrate along the grain boundaries of the perovskite crystals and into the adjacent charge transporting layers, or even into the metal electrodes of the solar cell. These behaviors readily lead to defect states (e.g., cations and halide vacancies) and metal halide formations, which severely degrade the device performance. [19,20] Moreover, the unfavorable volume expansion of the perovskite lattice under continuous thermal stresses accelerates the moisture diffusion, further deteriorating the quality of perovskite film. [21] Thus, improving the stability of PSCs in moist and thermally elevated environments is greatly demanded. Defects in perovskite crystals, such as the vacancies of perovskite constituent, grain boundaries, and uncoordinated Pb 2+ ions, become the source of nonradiative recombination centers, which can adversely affect the device performance of PSCs as well as the operational stability. However, pristine perovskite films are typically known to be quite vulnerable to intrinsic defect generation. [22,23] Therefore, to minimize the defect formation and thus achieve high-quality perovskite layers with large grain size and uniform surface morphology, researchers have added cations or anions, applied antisolvent treatments, and modified neighboring layers. [24,25] Chemical additives have Significant efforts have been devoted to modulating the grain size and improving the film quality of perovskite in perovskite solar cells (PSCs). Adding materials to the perovskite is especially promising for high-performance PSCs, because the additives effectively control the crystal structure. Although the additive engineering approach has substantially boosted the efficiency of PSCs, instability of the perovskite film has remained a primary bottleneck for the commercialization of PSCs. Herein, a newly conceived bithiophene-based n-...

Toward high‐efficiency stable 2D/3D perovskite solar cells by incorporating multifunctional CNT:TiO2 additives into 3D perovskite layer

“…In this study, we can improve the charge transport of 2D M 2 A n ‐1 B n X 3 n +1 layer by additive strategy instead of increasing n . The second one is that the defects including the vacancies of perovskite constituent and uncoordinated Pb 2+ ions in 3D perovskite crystals and grain boundaries (GBs) are still not eliminated, which can degrade device efficiency and stability 42 . Typically, when the solution method is used, the formation of defects in polycrystalline films is inevitable 43 .…”

Emerging Perovskite Solar Cell Technology: Remedial Actions for the Foremost Challenges

“…has introduced a rod‐shaped n‐type organic small molecule, (5Z,5′Z)‐5,5′‐((7,7′‐(3,3′‐dioctyl‐[2,2′‐bithiophene]‐5,5′‐diyl) bis(benzo[c] [ 1,2,5 ] thiadiazole‐7,4‐diyl)) bis(methanylylidene) bis(3‐ethyl‐2‐thioxothiazolidin‐4‐one (Y‐Th2), to combat against operational stability under humid conditions. [ 220 ] The passivation of Y‐Th2 can form a Lewis acid–base interaction with the Pb + ions, which increases a Lewis acid–base interaction with the Pb 2+ ions. Subsequently, this increases the Gibbs free energy of nucleating perovskite crystals.…”

“…Reproduced with permission. [ 220 ] Copyright 2020, Wiley‐VCH. g) J–V curves of PSCs with and without KPF6 measured in different scan directions.…”

“…[ 287,288 ] Perovskite surface passivation treatment. [ 218,220 ] Suppression of ion migration. [ 233–237 ] Device encapsulation.…”

Surface Modification of Cs0.1(CH3NH3)0.9PbI3 by Isopropanol as Green Antisolvent for Efficiency Enhancement of Perovskite Solar Cells

“…Surface modification of perovskite films can be symmetrically controlled and conducted by various methods such as solvent engineering, [ 5–7 ] vacuum evaporation, [ 8–10 ] additive‐assisted deposition, [ 11–13 ] ASAC, [ 14–16 ] etc. Commonly, surface modification using the ASAC method can easily be applied during the perovskite film processes, which can accelerate the nucleation rate, crystal growth rate, and improve surface properties of perovskite films.…”