Abstract
Organic-inorganic halide perovskite materials have been touted for their excellent light-absorbing properties, implying great potential for low-cost fabrication of high-performance solar cells. Nevertheless, numerous studies revealed that choice of materials and optimization of device architecture is crucial for realizing high efficiency photovoltaics consisting perovskite photoactive materials. PEDOT:PSS, poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate), has been widely selected as a hole transport material, for its high transparency, which allows enough light to the photoactive layer. However, perovskite solar cells with PEDOT:PSS hole transport layer often suffers low stability, due to the high acidity compared to the other devices.
In this research, we introduce various effective solutions for controlling electrical and chemical properties of PEDOT:PSS, for realization of high efficiency and stability of perovskite solar cells. Introducing inorganic copper-based chalcogenide, (such as copper sulfide, Cu2-xS) nanoparticles [1] and organic nanosheets [2] (covalent organic nanosheets, CONs) to PEDOT:PSS hole transport layer resulted in improved charge dynamics factors and device performance. The incorporation of the CuS nanoparticles induced interaction between PEDOT molecules and the particles, which resulted in structural transition of PEDOT:PSS and its higher hole mobility. Interestingly, UV-selective absorbing properties of CuS particles reduced photo-induced damage on perovskite materials, by filtering UV light from the sunlight which enhanced the devices' stability significantly. On the other hand, the additional organic interlayer between PEDOT:PSS and hole-selective electrode facilitates formation of even film morphology, which contributed to the higher crystallinity of perovskite layers and enhanced charge separation, which resulted in higher performance compared to the pristine device. Suppressing acidity of PEDOT:PSS layer has been another target for enhancing stability of perovskite solar cells. Acidity modification by incorporation of imidazole [3] not only prevented unintentional degradation of device structure, and the PEDOT:PSS with modified pH brought about higher performance which originated from tuned surface properties and molecular rearrangement, which resulted in better crystallization of perovskite coated onto the PEDOT:PSS layers, and efficient charge transport. Also, tailoring ratio of amount of PEDOT to PSS molecules by inducing solution reaction between neutral and acid PEDOT:PSS [4] revealed encouraging electric properties and stability of PEDOT:PSS hole transport layer. This work provides solutions for effective tailoring of electrical and chemical properties of PEDOT:PSS, which will shed light on the low-cost and reliable fabrication of perovskite photovoltaics.
[1] Kim, B. G., Jang, W., Choa, Y. H., and Wang, D. H., ACS Sustain. Chem. Eng., 2020, 8, 20, 7617–7627.
[2] Park, S., Kim, M. S., Jang, W., Park, J. K., and Wang, D. H. Nanoscale, 2018, 10, 4708-4717.
[3] Yi, M., Jang, W., and Wang, D. H. (2019). ACS Sustain. Chem. Eng., 2019, 7, 8245–8254.
[4] Kim, M., Yi, M., Jang, W., Kim, J. K., and Wang, D. H. Polymers, 2020, 12, 129.