A recent article in the Royal Society of Chemistry conducted by Researchers at the University of Manchester’s School of Materials, Photon Science Institute and School of Chemistry, demonstrates the use of polystyrene (PS) microgel particles (PM) as a substitute for hole transport material (HTM) in the manufacturing of perovskite solar cells (PSCs).
This new generation of solar cells developed by Brian Saunders’ team at the University of Manchester could significantly reduce the cost of production of PSCs in the future, thereby allowing for the production of electricity by solar power to be a more affordable and realistic option.
While traditional photovoltaic (PV) cells, which function by converting light energy to electricity, utilize silicon to harvest the light energy, this process is typically energy intensive, thereby increasing the cost associated with the production of these cells. The PSCs, which uses perovskite instead of silicon, are being widely used as an alternative to silicon-PVs due to the perovskite material being much less expensive.
Although the power conversion efficiency (PCE) of the PSCs is still not on par with that of the PV cells, recent improvements in the technology over the past several decades has led to the better development of PSCs.
The perovskite material used in PSCs is vulnerable to degradation as a result of their exposure to moisture, light, oxygen and high temperatures. The HTM materials used in the PSC such as Spiro-MeeOTAD (spiro), poly(3-hexylthiophene) (P3HT) and poly (triaryl amine) (PTAA) acts as a barrier to protect the perovskite from degradation, which serves a crucial role in ensuring the adequate performance of these devices.
Despite this, these HTM materials are relatively expensive, contributing to a significant amount of the PSCs cost, therefore, materials that can improve the stability of and reduce the costs associated with PSCs is gaining great interest among the Researchers in this field.
Polystyrene microgels (MGs) are sub-micrometer cross-linked polymer particles that are hydrophobic, but capable of swelling when presented in a good solvent. Based on previous findings that confirmed MGs to increase the structural order, light absorption and conductivity preservation within composite MG-P3HT films, Saunders’ team investigated whether MGs could increase the stability of PSCs and replace a majority of the HTM phase used in the PSCs.
To do this, the team of Researchers utilized scalable-emulsion polymerization technique to prepare polystyrene-MGs that are cross-linked by divinyl benzene (DVB).
The MG particles were mixed with HTM materials such as spiro, P3HT and PTAA to create mixed dispersions of HTM/MG. While the spiro-MG composites formed micro-cracks due to the inability of the spiro molecules to interdigitate, the P3HT-MG and PTAA-MG formed mechanically robust composites. The mixed dispersions of P3HT-MG and PTAA-MG are further used to coat the surface of the PSCs using spin coating.
Although the HTMs, P3HT and PTAA were used as minority phases occupying less than 35% weight of the composite HTM while the MGs composition was 65% weight, the efficiencies of the P3HT-MG and PTAA-MG decreased only by 20% compared to the control PSC made of just P3HT and PTAA. The current research also found that MGs were well dispersed within the PTAA matrix. The open circuit voltages for the P3HT-MG PSCs was found to increase by 170 mV compared to the control PSCs. Interestingly, the solar cell stability of P3HT-MG and PTAA-MG composites was also found to be far superior than the control PSCs. Furthermore, the PTAA-MG films were found to be highly efficient in quenching MAPI (C) fluorescence despite of the 65% use of MGs.
The current research suggests that use of MGs, especially as conjugate polymers, in the manufacturing of PSCs could significantly decrease the cost of the PSC cells due to the scalability of the making MGs and the increased performance stability of the PSCs made from composites. Due to the ability of MGs to be readily functionalized, MGs serve as excellent vehicles for introducing diversity into future PSCs made from composite HTMs, which could have a variety of applications in the future.
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- “Reducing hole transporter use and increasing perovskite solar cell stability with dual-role polystyrene microgel particles” Chen, M., Mokhtar, M., et al. Nanoscale. (2017). DOI: 10.1039/C79R02650A.