Sodium Benzenesulfonate Modified Poly (3,4‐Ethylenedioxythiophene):Polystyrene Sulfonate with Improved Wettability and Work Function for Efficient and Stable Perovskite Solar Cells

Abstract

The increasing interest in high-performance and economical photovoltaic materials has heightened the emergency to develop the organic-inorganic hybrid halide perovskite solar cells (PSCs). Since the debut of PSCs proposed by Miyasaka et al. in 2009, the PSCs community has achieved great success such as the rocketing power conversion efficiency (PCE) from the initial 3.8% to the latest 25.5% in 2020 in single-junction architectures, and to 29.1% in silicon-based tandem cells. [1-5] This eye-catching breakthrough is contributed by the numerous merits of perovskite material such as long carrier-diffusion length, proper bandgap (1.5-1.6 eV), and facile solution processing. [6-10] In general, the PSCs are classified by architecture into normal (n-i-p) and inverted (p-in) structures, where the perovskite layer is sandwiched between the electron transport layer (ETL) and hole transport layer (HTL). [11,12] For the normal-structured PSCs, metal oxides such as SnO 2 and TiO 2 are commonly used as the bottom ETL, whereas the organic materials such as Spiro-OMeTAD are used as HTL. [13,14] The PSCs feature high efficiency up to 24.82% by introducing fluorinated isomeric analogs in Spiro-OMeTAD. [15] However, the normal-structured PSCs with high PCE are usually based on mesoscopic n-type TiO 2 or insulating Al 2 O 3 to accelerate electron mobility, while the high sintering temperature (>450 C) limits the application in low-cost flexible devices. [16,17] Meanwhile, the upper HTL used organic materials is extremely costly and unstable in air. In contrast, the bottom HTL of inverted (p-in) PSCs is low-temperature processable (<100 C) and cheaper. Therefore, the inverted planar PSCs have a wider application prospect on account of lowtemperature preparation, excellent reproducibility, and negligible hysteresis. [18,19] In addition, the efficiency of the small-area inverted planar PSCs has reached a certified value of 22.3%. [20] Also the record efficiency of over 18% for a mini-module has been achieved in an aperture area of 19.276 cm 2. [21] These results indicate that the inverted structure may be more suitable for manufacturing large-area cells with long-term stability and outstanding efficiency, which means inverted planar PSCs have a better prospect in commercialization. The most common structure of the inverted PSCs is indium tin oxide (ITO)/Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS)/perovskite/PCBM/metal electrode. [22,23] PEDOT:PSS is the most extensively used hole transfer material in inverted PSCs due to its optical transparency, high thermal stability, and good mechanical flexibility.

Review on Tailoring PEDOT:PSS Layer for Improved Device Stability of Perovskite Solar Cells

“…Table 1 lists the PCE and long-term stability of PSCs adopting PEDOT:PSS as HTL in previous research work. Generally, modification methods can be classified into three types: doping [61,[78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94], post-treatment [62,[95][96][97] and using bilayer [98][99][100][101][102]. Furthermore, there are some other methods reported to modify the properties of PEDOT:PSS for improving the device stability, such as, using other dopants to replace PSS [56,103], and developing new processing methods of PEDOT:PSS film [104,105], which are discussed in Section 3.…”

“…It has been proved that the conductivity of PEDOT:PSS can be increased from 10 −2 to 10 3 S/cm by doping an organic compound, such as ethylene glycol (EG), dimethyl sulfoxide (DMSO), an ionic liquid, an anionic surfactant, or dimethyl sulfate, into PEDOT:PSS aqueous solution [23][24][25][26][27][28][29]. Besides conductivity, other properties, such as work function, acidity and hydrophilic properties, can also be modified using the doping method [61,[78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94].…”

“…Large grain size indicates better crystallinity and fewer grain boundaries, where the humidity could penetrate the perovskite film. The fewer grain boundaries of the perovskite layer contribute to higher humidity stability [92]. Li et al demonstrated that doping PEDOT:PSS with sodium benzenesulfonate (SBS) can improve the device performance of inverted PSCs with enhanced stability.…”

“…It was observed that the modified PEDOT:PSS was more smooth and had higher conductivity, leading to better crystallinity in the perovskite film. The PCE can retain 90% after 20 days storage in air [92]. Zhou et al found that ionic liquid can also increase the conductivity of PEDOT:PSS.…”

Enhancement of Volumetric Capacitance of Binder-Free Single-Walled Carbon Nanotube Film via Fluorination

“…The depletion of fossil fuels causes fluctuations in their price and leads to problems with pollution of air and soil. Therefore, recently there has been a growing interest in the development of highly efficient energy storage devices, including solar cells [ 1 , 2 ], rechargeable batteries [ 3 ], and electrochemical double-layer capacitors (EDLCs) [ 4 , 5 ]. EDLCs provide high power density, a long-term cycle life, and are environmentally friendly [ 6 ].…”