Efficient Bifacial Passivation with Crosslinked Thioctic Acid for High‐Performance Methylammonium Lead Iodide Perovskite Solar Cells

Abstract

Organic-inorganic hybrid halide perovskite materials have been used in optoelectronic applications, including photodetectors, X-ray imaging, lasing, photocatalysis, lightemitting diodes, and so on. [1][2][3][4][5] Owing to their high optical absorption coefficient, low exciton binding energy, long charge carrier diffusion lengths, high photoluminescence (PL) quantum yield, suitable bandgap, and energy level, perovskite solar cells (PSCs) are emerging as promising candidates for the next-generation thin-film solar cells. [6][7][8][9][10][11] By optimizing the perovskite compositions, device structures, and deposition methods, power conversion efficiency (PCE) of PSCs has been dramatically increased from 3.8% in 2009 to the latest certified value of 25.2%, approaching the champion efficiency of the industry silicon solar cells. [12][13][14][15][16][17] The traditional lowtemperature solution-processing and fast crystallization method are widely used in synthesis of perovskite films, which inevitably introduce a large amount of defects into perovskite bulk and perovskite-transport layer interfaces (PTLIs). [18,19] Herein, PTLIs refer to the interfaces of both electron transport layer (ETL)/perovskite and perovskite/hole transport layer (HTL). It is well known that the defects can act as charge recombination centers to induce severe energy loss, thereby reducing the device efficiency. [18] Meanwhile, these trap states create conditions for the infiltration of moisture and oxygen into perovskite layer and subsequently seriously decrease the device stability. [20][21][22] Moreover, several recent studies show that defects mainly present at the PTLIs (called interface defects), which are strongly associated with the energy level alignment, charge dynamics, photocurrent hysteresis, and the long-term operational stability. [23][24][25] Therefore, it is imperative to seek an effective way to reduce the defects, especially at the PTLIs, for achieving the high-performance PSCs. Additive engineering [26][27][28][29][30][31][32][33][34] and interface engineering [35][36][37][38][39][40][41] have been regarded as effective strategies to reduce the defect density in PSCs, such as incorporating Phenyl-C61-butyric acid methyl ester (PCBM) [29] into perovskite layer to effectively passivate the defects and minimize the photocurrent hysteresis, inserting self-assembled monolayer of organic molecules with functional groups [36,37] into perovskite/ETL interface to suppress defects Defects, inevitably produced within bulk and at perovskite-transport layer interfaces (PTLIs), are detrimental to power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). It is demonstrated that a crosslinkable organic small molecule thioctic acid (TA), which can simultaneously be chemically anchored to the surface of TiO 2 and methylammonium lead iodide (MAPbI 3 ) through coordination effects and then in situ crosslinked to form a robust continuous polymer (Poly(TA)) network after thermal treatment, can be introduced into PSCs as a ...

Examining the Interfacial Defect Passivation with Chlorinated Organic Salt for Highly Efficient and Stable Perovskite Solar Cells

“…[ 17 ] Moreover, previously reported work indicated that trap states mainly located at the interfaces of multilayers of whole device (called interface defects) and at the perovskite surface (called surface defects), which are effectively related to the energy level matching, hysteresis, charge carriers dynamics, and the long‐term environmental and operational stability. [ 18–22 ] Therefore, it is indispensable to explore an impressive way to diminish the defects, particularly at the interfaces, for acquiring the high‐efficient and stable PSCs. Currently, there are lots of approaches to improve the performance and stability of PSCs, containing additive engineering, using additive into a perovskite absorber layer and interface engineering, modifying the hole transport layer (HTL)/perovskite or perovskite/electron transport layer (ETL) interfaces.…”

The J–V Hysteresis Behavior and Solutions in Perovskite Solar Cells

“…[ 126 ] As shown in Figure a, the crosslinkable thioctic acid (TA) can in situ crosslinked to form a polymer (poly(TA)) network after thermal treatment, effectively passivate defects in the perovskite film. [ 122 ] Moreover, the —COOH group in TA can interact with PbI 2 and TA is chemically bonded to GBs. Therefore, the finally prepared PSCs show negligible hysteresis benefit from the low defect density in the perovskite film.…”

“…Reproduced with permission. [ 122 ] Copyright 2020, Wiley‐VCH Publications. b) Molecular structure of DMF, GBL, NMP, and DMSO.…”

“…Additives can be introduced during the preparation of the perovskite film. [121,122] In recent years, ionic liquids have been gradually used in PSCs. Ionic liquid methylammonium acetate (MAAc) as an additive used in 2D perovskite, which improved the performance and achieved hysteresis-free by affecting the crystallization and morphology of the perovskite film.…”

Multilayer Cascade Charge Transport Layer for High‐Performance Inverted Mesoscopic All‐Inorganic and Hybrid Wide‐Bandgap Perovskite Solar Cells

“…It is well known that the key factors influencing the overall device efficiency should be: 1) the film quality of all functional layers, especially for light absorber and charge transport layers (CTLs); 2) optoelectronic properties of CTLs, such as bandgaps, carrier mobility, and energy levels. [ 20–23 ] Therefore, obtaining high‐quality perovskite film with reduced defects is the prerequisite for high‐performance solar cells. Thus, far ion doping, such as Eu 2+ , [ 24 ] Mn 2+ , [ 25 ] Nb 5+ , [ 26 ] Cu 2+ , [ 27 ] Cl − , [ 25 ] and Br − , [ 28 ] has been proven to be an effective strategy to obtain large grains and in situ strengthen original octahedral structural stability in all‐inorganic perovskite system.…”