Four-terminal perovskite/silicon tandem cell is reported with power conversion efficiency > 29%, where top perovskite subcell uses an optimal thickness of Al2O3 passivation layer and transparent electrode engineering with customized metallization scheme to overcome performance losses in terms of open circuit voltage and fill factor.
Four-terminal (4-T) perovskite/silicon tandem solar cell is crucial due to the different lifetime of top near-infrared transparent (NIRT) perovskite solar cell (PSC) and bottom silicon (Si) solar cell, and it allows for independent optimization and operation of the top and bottom subcells. Knowing the fact that Si solar cells are well established, we take the opportunity to explore NIRT-PSC which is still reported by selective groups because of challenges associated with sputtered transparent conducting electrode (TCE) deposition. In this study, we have emphasized on passivation engineering, scalability, modifications to the absorber layer thickness, and advancements in electrode design to improve the performance of NIRT-PSC. First, we have optimized thickness of passivating aluminum oxide (Al2O3) for p-i-n PSCs device with wide bandgap (Eg = 1.67 eV) perovskite absorber. We have achieved power conversion efficiency (PCE) of 20.20% with active area of 0.056 cm2 and 19.16% with active area of 0.175 cm2 by using an optimized thickness of Al2O3 (3 nm) interlayer for opaque devices. Additionally, Al2O3 passivated devices (T80 > 1600 h) demonstrated improved stability compared to control devices (T80 ∼ 100 h) under identical measurement conditions. Building on this optimized passivation strategy, we extended the design to NIRT-PSCs, which are crucial for 4-T tandem solar cells. For optimized NIRT-PSCs, (i) we have used thicker perovskite layer, as TCEs do not provide the benefit of back reflection, and (ii) metallization of transparent conducting electrodes to mitigate higher sheet resistance of TCE compared to opaque electrodes. With optimized NIRT-PSCs, we have achieved PCE of 29.14% & 26.86% for active areas of 0.175 and 1.08 cm2, respectively, in 4-T perovskite/Si tandem solar cell, where the bottom Si solar cell has the PCE = 25.5%.
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