Semitransparent perovskite solar cells (ST-PSCs) are critical components for tandem applications, where their integration with other photovoltaic technologies, resulting in perovskite/silicon, all-perovskite, or perovskite/CIGS tandem devices, can overcome the single junction limit.[1, 2] A key challenge in fabricating ST-PSCs is protecting the underlying layers from damage caused by the sputtering process used to deposit transparent electrodes. This protection has conventionally been achieved using buffer layers deposited via atomic layer deposition (ALD).[3, 4] However, ALD requires specialized equipment not available in all laboratories and represents an expensive, time-consuming process, limiting its widespread adoption.

In this study, we present a cost-effective, universally applicable solution-processed buffer layer based on metal-oxide nanoparticles. To identify the optimal buffer layer, we systematically evaluated a variety of metal-oxide nanoparticles for their ability to mitigate sputtering-induced damage. Photoluminescence (PL) quenching measurements were employed to assess damage levels, revealing that certain materials exhibited higher defect densities after the sputtering process. In addition, absorbance measurements provided insights into the UV shielding performance of these materials during sputtering. Analysis of their crystal structures further revealed either preferential crystal growth, which enhanced charge transport, or amorphous structures, depending on the nanoparticle type. These combined insights enabled the selection of an optimal solution-processed buffer layer with superior protective and functional properties.

We demonstrate the efficacy of this buffer layer in monolithic tandem device configurations, including perovskite-CIGS tandems, all-perovskite tandems, and perovskite/silicon tandems. For the latter, we integrate an optimized ST-PSC with a polished front-side/unpolished rear-side p-type silicon heterojunction (SHJ) solar cell. The intrinsic roughness of the unpolished rear-side significantly enhances light absorption, eliminating the need for a dedicated texturization step. This innovation enables a final tandem efficiency of 25.3%, illustrating the potential of combining solution-processed buffer layers with unpolished silicon wafers for higher photocurrent generation.

Our findings highlight the scalability and versatility of solution-processed buffer layers as a practical solution for perovskite-based tandem solar cells. The universal nature of this buffer layer allows it to be employed in various tandem configurations, including perovskite-CIGS and all-perovskite tandem solar cells, broadening its applicability and impact across tandem technologies.

References:

[1]    W. Shockley and H. J. Queisser, J. Appl. Phys. (1961), vol. 32, no. 3, pp. 510–519.

[2]    A. De Vos, J. Phys. D. Appl. Phys. (1980), vol. 13, no. 5, pp. 839–846.

[3]    S. Mariotti et al, Science (2023)., vol. 381, no. 6653, pp. 63–69.

[4]    E. Aydin et al., Nature (2023), vol. 623, no. 7988, pp. 732–738.