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| Fig. 1: Diagram of crystalline perovskite. The blue and black spheres represent cations, while the red spheres represent anions. (Source: Wikimedia Commons.) |
As the world attempts to transition from non-renewable sources of energy such as petroleum and natural gas to renewable sources, solar energy is increasingly looked to by many in both the public and private sectors as a source of cheap, reliable power that could replace a substantial component of the current input into the electric grid. Solar energy creates power by agglomerating the output of many solar panels that are placed in a given location. Solar panels are made up of smaller units called solar cells; when exposed to photons in sunlight, electrons in the inner layers of the solar cell are energized, creating usable electric current. The most common type of commercially available solar cell uses monocrystalline silicon as the semiconductor material placed in the active layer of the solar cell. [1] However, the manufacturing process for silicon solar cells requires intense heat to remove impurities, and the theoretical limit of single-junction silicon solar cells is quickly being approached. [2] As such, there has been a great deal of interest in recent years to investigate alternatives to silicon. A different type of semiconducting material, called perovskites, has garnered much of this recent attention by both the public and private sectors, and shows promising results for future solar cells.
Perovskites are a class of materials that have the same crystalline structure as calcium titanium oxide (chemical formula CaTiO3) and have the general chemical structure ABX3, where A and B represent cations of different sizes, and X represents an organic anion. [3] Perovskite solar cells work in a similar way to silicon solar cells, with the perovskite taking the place of silicon as the active light-harvesting layer in the solar cell.
Proponents of perovskite solar cell technology cite several advantages over traditional silicon solar cells - perovskite cells have a lower intergranular defect density than silicon cells, which removes the need for an intense purification process during manufacturing. [4] They also have much higher optical absorption compared to silicon solar cells, which reduces the required thickness of the cells thin. [4] Perovskite is also more physically flexible than silicon, and can be manufactured from commonly available materials - in fact, Rolston et al. were able to develop a fast method to spray films of perovskite onto a pane of glass through a robotically-controlled nozzle, thereby creating a solar cell. [5]
However, the most import current disadvantage to perovskite solar cells is their lifetime. While many commercially available silicon solar cells are warrantied to last 25 years, perovskite solar cells are far more susceptible to environmental conditions like humidity and blunt force impact, and degrade much more quickly. [6] As such, they have significantly shorter lifetimes than silicon solar cells. Additionally, perovskite solar cells are currently less efficient than silicon solar cells, which compounds the disadvantage of the technology. [2]
Still, proponents of perovskite solar cell technology argue that these drawbacks are rapidly being addressed in the research lab, and the significantly lower cost of perovskite cells should provide the impetus for investment today.
To analyze the viability of perovskite solar cells modules as replacements for silicon solar cells, we will compute the cost per year for each type of cell technology. The comparative cost, efficiency and service life of perovskite and silicon solar cells is given in the Table 1.
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| Table 1: Solar cell specifications from Meng et al. [7] |
If we take the irradiance of the Earth at standard testing conditions to be 1000 watts per square meter, and if we assume that we are testing solar cells with an area of 1 square meter, then we have that the cost to operate a perovskite solar cell is
| $0.15 W-1 × 0.233
× 1000 W m-2 1 year |
= | $34.95 m-2 y-1 |
and that the cost to operate a silicon solar cell is
| $0.30 W-1 × 0.266
× 1000 W m2 25 years |
= | $3.19 m-2 y-1 |
As such, perovskite solar cells are roughly an order of magnitude more expensive to run per year than silicon cells.
Although the analysis above showed that perovskite solar cells are not yet ready for industrial deployment, the cost benefits associated with the manufacturing process, combined with the rapidly increasing energy efficiency and recent research efforts into increasing the stability of perovskite solar cells shows that they are still a promising technology for the future. [8]
© Nikesh Mishra. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] B. L. Smith et al., "Photovoltaic (PV) Module Technologies: 2020 Benchmark Costs and Technology Evolution Framework Results," U.S. National Renewable Energy Laboratory, NREL/TP-7A40-78173, November 2021.
[2] N. Shrivastav et al., "Investigations Aimed at Producing 33% Efficient Perovskite-Silicon Tandem Solar Cells Through Device Simulations," RSC Adv. 11 37366 (2021).
[3] B. Knapp, "How Feasible Is Perovskite Solar Technology?," Physics 240, Stanford University, Fall 2018.
[4] M. A. Green, A. Ho-Baillie, and H. J. Snaith, "The Emergence of Perovskite Solar Cells," Nat. Photonics 8, 506 (2014)
[5] N. Rolston et al., "Rapid Open-Air Fabrication of Perovskite Solar Modules," Joule 4, 2675 (2020).
[6] D. A. Quansah et al., "Reliability and Degradation of Solar PV Modules - Case Study of 19-Year-Old Polycrystalline Modules in Ghana." Technologies 5, 22 (2017).
[7] L. Meng, J. You, and Y. Yang," Addressing the Stability Issue of Perovskite Solar Cells For Commercial Applications," Nat. Commun. 9, 5265 (2018).
[8] X. Zhao et al., "Accelerated Aging of All-Inorganic, Interface-Stabilized Perovskite Solar Cells," Science 377, 307 (2022).
