Chinese scientists have proposed a new structure scheme for perovskite batteries, which has achieved a world record in terms of the steady-state certified efficiency of pin trans-structure devices. This breakthrough has solved the "passivation-transmission" contradiction problem, which has been a long-standing issue in perovskite solar cells.
The “Passivation- Transport” Contradiction Problem
The contradiction between passivation and transport has been a ubiquitous problem in optoelectronic devices, including solar cells, light-emitting diodes, photodetectors, and more. In order to reduce the non-radiative recombination loss on the semiconductor surface, a passivation layer is used to reduce the defect density of the semiconductor surface. However, the conductivity of these passivation materials is generally very low. Increasing their thickness enhances the passivation effect but limits current transmission. This contradiction means that the thickness of these ultra-thin passivation layers must be precisely controlled within a few nanometers, which is not suitable for low-cost large-area production.
Perovskite Solar Cell Technology
Perovskite solar cell technology has attracted widespread attention in recent years as it provides new low-cost and high-efficiency photovoltaic solutions. The non-radiative recombination loss caused by the heterojunction contact problem has been shown to be the main performance limiting factor. Due to the "passivation-transport" contradiction problem, the thickness change of the ultra-thin passivation layer at the nanometer level causes a decrease in fill factor and current density. Therefore, all types of perovskite devices need a new type of contact structure, which can reduce the sensitivity of passivation thickness and improve performance.
The PIC Contact Structure Scheme
After long-term thinking and a lot of experimental exploration, Professor Xu Jixian’s team and collaborators from the University of Science and Technology of China proposed the PIC contact structure scheme. The main idea is to use a porous insulating layer with a thickness of hundreds of nanometers instead of the traditional nano-scale passivation layer and tunneling transport. This forces carriers to transport through the local open area while reducing the contact area. The team's semiconductor device modeling calculations reveal that the period of this PIC structure should match the carrier transport length of the perovskite.
Verification of the PIC Scheme
The team carried out the verification of the PIC scheme in the pin trans structure widely used in stacked devices. They realized that the hole interface recombination velocity dropped from ~60cm/s to 10cm/s, and 25.5% of the single junction highest efficiency (record 24.7% certified steady-state efficiency for pin structure) was achieved. This substantial improvement in performance is common in perovskites with a variety of band gaps and compositions, demonstrating the broad application prospects of PICs. In addition, the PIC structure has achieved the improvement of perovskite film coverage and crystal quality on various hydrophobic substrates.
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| Figure 1. PIC (porous insulator contact) design principle and device simulation |
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| Figure 2. Based on the nanosheet size effect to regulate the island growth mode to realize the PIC structure |
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| Figure 3. PIC suppression of nonradiative recombination at the interface and bulk of the perovskite |
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| Figure 4. PIC structure verification in pin trans device |
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