In the field of solar energy, researchers are constantly striving to improve the efficiency of photovoltaic cells. A paper published in Advanced Materials presents innovative photovoltaic architectures that could overcome the single-junction limit and provide new insights into solar energy conversion efficiency.
Photovoltaic technology is considered one of the pillars of the transition to a sustainable society. The efficiency of converting solar energy into electricity is further limited by the so-called “single junction limit”.
This is because photons above the bandgap of the semiconductor are absorbed but lose excess energy (thermalization losses), while photons below the bandgap are not absorbed by the semiconductor (transmission losses). This limit is just under 33%. under AM1.5 conditions for an ideal semiconductor material.
Innovative photovoltaic architectures
Researchers have identified two architectures that, with appropriate complexity, could push the single-junction limit of photovoltaic power conversion.
The first is a vertical “staggered half octave” system where selective absorption allows the use of 6 different band gaps.
The second is the lateral “overlapping rainbow” system, in which selective irradiation allows the use of a narrow-band energy acceptor with reduced voltage losses according to the energy gap law.
Both of these architectures would be very resilient to spectral changes, unlike two-port, multi-junction architectures which are limited by the Kirchhoff's law.
Figure 1.a) Architectures, level diagrams and transfer processes for radiation and charge transfer coupled up- and down-conversion materials (UC and DC, respectively), summarized as multi-exciton generation (MEG) and a double-junction system. The abbreviations for the layers are as follows: HTL: hole transport layer, ETL: electron transport layer, SC: active layer including the semiconductor, E: semi-transparent electrode, R: recombination layer. b) Corresponding equivalent circuits, c) Unique schematic representation of vertical and lateral multi-connection stacks, d) Features of the corresponding Python classes in the BOAR simulation and optimization environment.
A simulation based on Bayesian optimization
The researchers presented a simulation environment based on Bayesian optimization that can predict and virtually optimize the electrical performance of multi-junction architectures, both vertical and lateral, in combination with up-conversion and down-conversion materials.
The impact of microstructure on performance is explicitly considered using machine-learned predictive models from high-throughput experiments on simpler architectures.
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The presented work opens new perspectives for improving the efficiency of photovoltaic cells. The proposed innovative architectures could overcome the limitation of single ports and thus offer significant potential to improve the efficiency of solar energy conversion.
Furthermore, the use of Bayesian optimization to simulate and optimize the electrical performance of these architectures represents an important advance in the field of solar energy research.
For better understanding
What is the single connection limit?
The single junction limit refers to the maximum efficiency that a semiconductor-based solar cell can achieve due to thermalization and transmission losses.
What two architectures are proposed to overcome this limit?
The two proposed architectures are the vertical “staggered half octave” system and the lateral “overlapping rainbow” system.
What is Bayesian Optimization?
Bayesian optimization is an optimization method that uses Bayes' theorem to update the probability distribution of a model's variables based on observed data.
What is the advantage of these new architectures?
These architectures would be very resilient to spectral changes, in contrast to two-port, multi-junction architectures that are constrained by Kirchhoff's law.
What impact does this research have on the field of solar energy?
This research opens new perspectives for improving the efficiency of photovoltaic cells, which could have a significant impact on the development of solar energy.
References
Lüer, L., Peters, IM, Le Corre, VM, Forberich, K., Guldi, DM, & Brabec, CJ (2023). Bypassing the single-junction limit with advanced photovoltaic architectures. Advanced materials. https://doi.org/10.1002/adma.202308578
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