Scientists in the US and China have collaborated on a new paper investigating the use of polyaniline as a material for improved perovskite solar cells. The findings of their research have been published online in ACS Applied Energy Materials.
Study: Electrochemically Prepared Polyaniline as an Alternative to Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) for Inverted Perovskite Solar Cells. Image Credit: Audio und werbung/Shutterstock.com
Perovskite Solar Cells
Solar power is a key technological solution to the world’s energy and climate change problems. Solar cell technology has existed for several decades, with considerable progress made in the field in recent years in both solar energy harvesting and storage.
Perovskite photovoltaic solar cells are a hybrid organic/inorganic technology. These advanced solar power devices have several benefits, including tunable band gaps, long charge carrier lifetimes, low exciton binding energies, and long diffusion lengths. Initially limited in terms of their power conversion efficiencies, in recent years, devices have been reported that possess over 25% power conversion efficiency.
PEDOT:PSS and Perovskites
PEDOT:PSS is a commonly used material in perovskites. This material is used as a hole transport layer between the photoactive perovskite layer and indium tin oxide layer. Using PEDOT:PSS markedly improves the power conversion efficiency of perovskite solar cells.
Several strategies have been explored in studies to further improve the electron transport in perovskites. Conjugated zwitterions have been employed as interlayers to lower the metal layer’s work function, and adding LiF layers has a positive influence on the device’s FF and Voc.
Doping PEDOT:PSS with materials such as NaCl and RbCl has effects such as enhanced electrical conductivity, enlarged crystal size, and hole transport. This strategy has a positive influence on the work function of perovskite layers and the overall power conversion efficiency of devices.
Several issues have been observed with PEDOT:PSS, however. One of the fundamental issues is the degradation of active layers and defect formation associated with the large particle size of this material. Moreover, the of this material as a hole transport layer is hindered by issues with low electrical conductivity limits and cost.
Overcoming these Challenges
Due to these issues, research has focused in recent years on using alternative materials as hole transport layers. Several inorganic materials have shown promise for this purpose, such as CuI, CuSCN, NiOx, MoS2, and CuOx. Another strategy that has been demonstrated to produce favorable power conversion efficiencies is using CPE-K in inverted perovskite solar cells.
Other materials explored as promising candidates include transparent conducting polymers, which display enhanced conductivity and stability. Amongst these polymeric materials, polyaniline (PANI) has shown particular promise.
Polyaniline has several beneficial attributes such as low cost, environmental stability, high performance, facile synthesis methods, thin film transparency, superior processibility, and high purity. These make it an ideal candidate for use in perovskite solar cell hole transport layers.
Several studies have investigated the benefits of polyaniline. This material can be easily synthesized from aniline by chemical, photochemical, electrochemical, and enzyme-catalyzed routes. Chemically synthesized PANI:PSS has been evaluated for use in inverted solar cells as a hole transport mechanism, with power conversion efficiencies of up to 11.67% reported.
Doping polyaniline with various chemicals has produced devices with competitive power conversion efficiencies of up to 15.42%. Researchers have developed large-area polyaniline films for the production of optoelectronic modules. Electrochemical polymerization has emerged as the preferred option for producing polyaniline films for use as hole transport mechanisms in perovskites.
The Study
The new paper has proposed a method for preparing polyaniline films for use in perovskites. The authors have prepared a p-type doped polyaniline-based hole transport layer using cyclic voltammetry.
High electrical conductivity was demonstrated in the synthesized polyaniline electrode using nitric acid doping. Experimental analysis and comparative photovoltaic studies demonstrated an enhanced power conversion efficiency of 16.94% in inverted perovskite solar cells, higher than previously reported with polyaniline-based hole transport mechanisms.
Preparing the inverted polyaniline-based perovskite solar cell via electrochemical methods produced a device with lower Voc and FF and higher Jsc compared to conventional PEDOT:PSS devices. The authors have attributed this to the lower work function of polyaniline compared to PEDOT:PSS. Voc is decreased, but hole extraction is enhanced. Work function was increased using LiTFSI doping of the electrolyte solution.
In Summary
The new paper has demonstrated a facile, low-cost fabrication route for polyaniline hole transport mechanisms that display enhanced power conversion efficiency compared to conventional PEDOT:PSS hole transport layers in perovskites. This provides a route toward low-cost, high-efficiency perovskite solar cells, with the potential to provide an advanced technological solution for the solar power industry.
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Further Reading
Mabrouk, S et al. (2022) Electrochemically Prepared Polyaniline as an Alternative to Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) for Inverted Perovskite Solar Cells ACS Applied Energy Materials [online] pubs.acs.org. Available at: https://pubs.acs.org/doi/10.1021/acsaem.2c00621
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