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| Fig. 1:Graph showing the best tested cell efficiencies by year, highlighting the emerging PV technologies like perovskite cells shown in orange highlighted yellow. [11] (Courtesy of the DOE.) |
As demand for renewable energy increases worldwide, and the clean energy transition continues, solar energy has become an increasingly cheap and scalable option that has been explored vigorously. Among renewable options, solar panels have continued to evolve and been widely adopted, but have been largely dominated by silicon solar cells, due to their cheap and scalable properties. [1]
The most common type of solar panels on the market are made of monocrystalline silicon. This is due to a variety of factors, for example the abundance of silicon, the ability to cast large rods improving scalability, and the stability of these panels, found to be up to 25 years. [2] However, as shown in Fig. 1, the monocrystalline single-junction silicon architecture is quickly reaching the Shockley-Queisser efficiency limit (31.6%). [3] However, this percentage is given in ideal conditions, and the actual possible tested efficiency turns out to be much lower (26.8%). [3]
With solar efficiency being paramount to the commercial success of solar panels, recent research efforts have thus been directed elsewhere. One of the most promising new technologies has been perovskite solar cells (PSCs), which boasts an already comparable test efficiency (26.7%) while still in the early stages of improvement. [4]
The main advantage provided by PSCs is efficiency, with the highest stable efficiency of a single-junction PSC reported at 26.7%, as shown in Fig. 1. [5] Although the power conversion efficiency has not caught up to the best silicon solar cells, the marked improvements being made year to year suggest a lot more growing room for PSCs.
PSCs suffer from a shortened lifespan, as the perovskite structure is prone to degrading under light exposure, moisture, and temperature changes. [6] Current PSCs display a commercial lifetime of 1-2 years, with laboratory lifetimes pushing 5-7 years. This is increasing steadily as new strategies to increase stability in certain conditions are applied. [7] For example, notable progress was made by Azmi et al. to passivate the perovskite structure using oleylammonium iodide molecules. [8] This adjusts the size of the 2D perovskite layers, improving the PSCs ability to resist moisture and humidity, achieving efficiency of 24.3% with 95% retention at 85°C and 85% relative humidity for 1000 hours. For reference, commercial silicon solar cells have a stable power conversion efficiency around 20% with 95% retention under these conditions. [6] Thermal cycling performed by Jiang et al. using a thin 35 nm conjugated polymer as a hole transport layer and more resistant back electrode show an impressive 95% retained efficiency after 1000 thermal cycles (-40°C to 85°C). [7]
As shown in the previous section, there is still a lot of work to be done to improve the stability and lifetime of PSCs. However, to analyze the viability of PSCs as an emerging technology, we will compute the cost for both current lifespans and ideal lab lifespans against current silicon lifespans based on cost per watt over predicted lifespan. [9]
Assuming the irradiance of Earth at standard conditions to be 1000 watts per square meter, with an array of solar cells of dimensions 1 m × 1 m, then we can calculate the cost of each solar cell architecture based on work from Mathews et al. in Table 1. [10]
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| Table 1: Solar cell costs, from Mathews et al. [10] |
For the silicon single-junction cell, we can estimate
| $0.25 W-1 × 0.222
× 1000 W m-2 20 yrs |
= | $2.775 m-2 y-1 |
for the perovskite single-junction cell, we can estimate
| $0.53 W-1 × 0.258
× 1000 W m-2 1.5 yrs |
= | $91.16 m-2 y-1 |
and for the ideal lab perovskite single-junction cell, we can estimate
| $0.44 W-1 × 0.258
× 1000 W m-2 6 yrs |
= | $18.92 m-2 y-1 |
These results for cost analysis lead us to believe that currently, PCSs are still far too expensive compared to current silicon solar cells. This is by nature of their order-of-magnitude shorter lifespan. However, Mathews et al. suggest that a $0.40 cost/W is commercially viable and scalable, which perovskites are quickly approaching. [10] What is more promising is that this cost of manufacturing PCSs has dropped significantly over the past two decades (22% yearly by company First Solar).
With silicon solar cells reaching their ideal efficiency limits, PSCs have quickly become the focus of much interest in both academia and industry, with huge pushes for improved efficiency as well as prolonged stability. Although this technology is not currently viable, mostly due to the quick degradation of the materials under moisture and heat, it is a promising architecture for future commercial solar panels. If the lifespan can be pushed out to a comparable 20-25 years like silicon solar panels through stability-enhancing methods, PSCs can be competitive with not only other solar options, but also with fossil fuels and natural gas.
© Charm Feng Ang. 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] R. Sharif et al., "A Comprehensive Review of the Current Progresses and Material Advances in Perovskite Solar Cells," Nanoscale Adv. 5, 3803 (2023).
[2] D. M. Atia et al., "Degradation and Energy Performance Evaluation of Mono-Crystalline Photovoltaic Modules in Egypt," Sci. Rep. 13, 13066 (2023).
[3] B. Ehrler et al., "Photovoltaics Reaching for the Shockley-Queisser Limit," ACS Energy Lett. 5, 3029 (2020).
[4] N. T. P. Hartono et al., "Stability Follows Efficiency Based on the Analysis of a Large Perovskite Solar Cells Ageing Dataset," Nat Commun. 14, 4869 (2023).
[5] M. A. Green et al., "Solar Cell Efficiency Tables (Version 64)," Prog. Photovolt.: Res. Appl. 32, 425 (2024).
[6] C. Harito et al., "Current Progress of Perovskite Solar Cells Stability with Bibliometric Study," Curr. Opin. Colloid Interface Sci. 74, 101862 (2024).
[7] Q. Jiang et al., "Towards Linking Lab and Field Lifetimes of Perovskite Solar Cells," Nature 623, 313 (2023).
[8] R. Azmi et al. "Damp Heat-Stable Perovskite Solar Cells with Tailored-Dimensionality 2D/3D Heterojunctions," Science 376, 73 (2022).
[9] N. Mishra, "Perovskite Solar Cells," Physics 240, Stanford University, Fall 2022.
[10] I. Mathews et al., "Economically Sustainable Growth of Perovskite Photovoltaics Manufacturing," Joule 4, 822 (2020).
[11] T. Sarver, A. Al-Qaraghuli, and L. L. Kazmerski, "A Comprehensive Review of the Impact of Dust on the Use of Solar Energy: History, Investigations, Results, Literature, and Mitigation Approaches," Renew Sustain, Energy Rev, 22, 698 (2013).