A paper recently published in the journal ACS Applied Electronic Materials reviewed the use of iron disulfide/pyrite in solar cells to improve their efficiency.
Study: Iron Pyrite in Photovoltaics: A Review on Recent Trends and Challenges. Image Credit: LukVFX/Shutterstock.com
The increasing demand for energy coupled with the rapid exhaustion of fossil fuels has increased the significance of renewable sources of energy generation. Solar cells have emerged as a suitable alternative as they represent a clean and sustainable way of energy generation. Solar cells are composed of various materials that define the performance of the cells.
Significant potential exists to improve the overall solar cell performance by introducing new materials. Iron pyrite or disulfide is one such material that has gained attention for photovoltaic (PV) cells owing to its low cost, suitable bandgap, and high absorption coefficient. Moreover, pyrite is nontoxic and abundant on earth, which makes it more suitable as a PV material.
In this study, researchers reviewed the recent advancements in the synthesis of pyrite and its use in solar cells.
Traditional synthesis routes, such as the solvothermal method, hydrothermal method, hot injection method, and electrodeposition method, were used extensively for the synthesis of different pyrite structures.
Advanced synthesis methods, such as sputtering, physical vapor deposition (PVD), and chemical vapor deposition (CVD), were also used for pyrite synthesis to achieve better control over the final product quality and experimental conditions.
Other methods that were used for pyrite synthesis include sequential evaporation, magnetic field-laser ablation, pulsed electron deposition, aerosol-assisted CVD, spray pyrolysis, biosynthesis, ball milling, and liquid phase exfoliation.
The hydrothermal method was used to synthesize pyrite nanoparticles, nanorods, nanotubes, nanocrystals, microspheres, nanocubic crystals, irregular microcubes, and flower-like pyrite at different reaction temperatures and duration.
The synthesized pyrite structures were used for mössbauer spectroscopy, thermoelectric analysis, and chromate ion reduction as supercapacitor electrodes and in lithium-ion batteries and quantum-dot-sensitized solar cells.
Pyrite nanospheres, nanoparticles, nanocrystals, thin films, and microspheres were synthesized using the solvothermal method. The fabricated pyrite structures were used for PV measurements and characterization and in sodium batteries.
The hot injection method was used to fabricate pyrite nanoparticles, nanocrystals, nanocubes, and one-dimensional (1D) and two-dimensional (2D) nanostructured pyrites. The synthesized pyrites were used for intrinsic energy storage, hydrogen evolution electrocatalysis, band gap tuning for photovoltaics, PV measurements, seed-stimulation, and as hole transport layer in cadmium tellurium (CdTe) solar cell.
Iron pyrite films were prepared using a novel hybrid system composed of a novel sputtering process along with co-evaporation and used the synthesized films as a hole transport layer in cadmium sulfur (CdS)/CdTe solar cells.
Use of Pyrite in Solar Cells
Dye-sensitized Solar Cells (DSSCs)
DSSCs have received significant attention in the last few years owing to their low cost, versatility, and efficiency compared to conventional solar cells. DSSCs consist of a working electrode, a sensitizer, an electrolyte, and a counter electrode (CE).
Although platinum is typically utilized as a CE in DSSCs, the metal is extremely expensive, which limits its use in commercial applications. Pyrite is considered a suitable alternative to platinum to platinum for CEs.
Cobalt-doped pyrite was used as CE in DSSCs, with the cobalt concentration varying from 0 to 0.5 in terms of the atomic ratio relative to iron. The increase in power conversion efficiency (PCE) was 7.16% when undoped pyrite was used as CE and 8.36% when both cobalt and iron concentration was equal in the CE. The rise in PCE was attributed to the increase in current density and fill factor.
A sulfur-doped graphene composite with pyrite was utilized as an electrocatalyst in DSSCs. The pyrite CE demonstrated a PCE of 8.1%, which was similar to the PCE of 8.3% achieved when platinum is used as CE. Moreover, the obtained pyrite structure displayed enhanced stability.
Hollow porous pyrite nanoparticles with 150 ± 25 nm diameter synthesized through sulfurization of iron oxide obtained from Prussian blue were used as CE in DSSCs. The synthesized hollow pyrite yielded a PCE of 7.31%.
Organic Photovoltaic Cells (OPVCs)
OPVCs/organic solar cells (OSCs) possess several benefits, such as mechanical flexibility and better tuning. Additionally, OPVCs can be manufactured in mild conditions, which makes them an attractive alternative to silicone-based solar cells.
OPVCs consist of a blended active layer containing both an n-type acceptor and p-type donor organic semiconductor between the electrodes made from transparent materials at the bottom and top.
Bulk heterojunction (BHJ) OPVCs displayed an efficiency of more than 17% in a tandem configuration. However, the efficiency of BHJ solar cells can be increased with the incorporation of advanced materials and better structural configuration.
A semispherical pyrite was synthesized and used as an electron acceptor layer in a BHJ using a glass/indium-tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/poly(thieno[3,4-b]thiophene-co-benzodithiophene): [6,6]-phenyl C71butyric acid methyl ester:iron pyrite (PTB7:PC71BM:FeS2)/poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-florene)-alt-2,7-(9,9-dioctylflorene)] (PFN)/field metal (FM) configuration.
FM was composed of 16.5% tin, 51% indium, and 32.5% bismuth. Active layers comprising PC71BM and PTB7 were utilized. Pyrite nanocrystals were introduced in 0 to 1% weight ratios.
The PCE was increased with the rising concentration of pyrite nanocrystals, with the highest PCE of 6.47% observed at 0.5% pyrite concentration as pyrite nanocrystals increased the pathways to charge transfer and accelerated charge dissociation.
Pyrite quantum dots prepared using a colloidal solvothermal route were utilized as an electron acceptor layer in a BHJ consisting of a mixture of [6,6]-phenyl-C60-butyric methyl ester (PCBM) and poly(3-hexylthiophene-2,5-diyl) (P3HT) as conjugated polymers.
The pyrite concentration varied from 10 to 40% wt. in P3HT, and the highest PCE of 3.62% was observed at 20% wt. Further increase in pyrite concentration resulted in a reduction in the PCE. The PCE without pyrite doping of the BHJ was 2.32%, which indicated the synergistic effects of pyrite.
Inorganic Solar Cells (ISCs)
ISCs comprise multiple subclasses of solar cells, including gallium−arsenide−germanium solar cells (GaAs), CdTe solar cells, copper−indium−gallium−selenide (CIGS) solar cells, and silicon-based solar cells, which are used extensively as solar cell systems.
Among them, silicon-based solar cells have gained more attention than other IPOs owing to their high efficiency of over 27%, high reliability, and lower operating and manufacturing costs.
Iron pyrite crystals doped with different nickel concentrations were synthesized using the hot injection method and then used as a hole transport layer in a CdTe solar cell. The PCE was highest at 0.05% nickel concentration and then decreased sharply when the concentration was increased beyond the optimum nickel concentration.
Similarly, the PCE of a copper/pyrite/gold CdTe solar cell was 12.7% compared to 11.8% in copper/gold cells without pyrite. The increase in PCE after the inclusion of pyrite was attributed to the significant reduction of the barrier height.
To summarize, the use of iron pyrite in solar cells can considerably increase their PCE. However, more research is required to investigate the feasibility of using this strategy on a commercial scale to meet future energy needs in a sustainable and eco-friendly manner.
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Nayfeh, A., Alhassan, S. M., Zaka, A. Iron Pyrite in Photovoltaics: A Review on Recent Trends and Challenges. ACS Applied Electronic Materials 2022. https://pubs.acs.org/doi/10.1021/acsaelm.2c00489
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