Researchers from China's Shenzhen University of Information Technology, Handan Polytechnic College and Harbin Institute of Technology have developed a new strategy to improve the performance of two-dimensional (2D) perovskite solar cells by introducing diethylammonium (DEA⁺) as a spacer cation, addressing the long-standing trade-off between stability and efficiency in these materials.
2D perovskites are seen as a promising alternative to their 3D counterparts due to their enhanced environmental stability, which originates from the incorporation of bulky organic spacer cations between inorganic layers. These spacers act as barriers against moisture and oxygen ingress, but they typically introduce insulating characteristics that hinder charge transport and reduce crystallinity. As a result, while 2D perovskites have achieved power conversion efficiencies (PCEs) up to 19.41%, further improvements are constrained by limited carrier mobility and suboptimal film quality. In this work, the researchers replaced the commonly used phenylethylammonium (PEA⁺) spacer with DEA⁺ in layered perovskite structures of the form A'₂MAₙ₋₁PbₙI₃ₙ₊₁, focusing on the n = 4 composition (DEA₂MA₃Pb₄I₁₃). Structural characterization revealed a substantial improvement in film morphology: DEA-based films exhibited grain sizes of approximately 1.5 μm, compared to less than 150 nm for PEA-based films. This increase in grain size is indicative of reduced grain boundary density, which directly lowers trap-assisted recombination and facilitates more efficient carrier transport.
Optoelectronic measurements further showed that DEA incorporation leads to enhanced light absorption and a slightly narrower bandgap of 1.580 eV, compared to 1.593 eV for PEA-based films at the same n value. This improved band alignment supports more effective charge separation and extraction, which was confirmed by time-resolved photoluminescence measurements indicating faster carrier dynamics.
The impact of these material improvements was demonstrated in flexible inverted perovskite solar cells fabricated on 100 mm × 100 mm substrates. Devices based on DEA₂MA₃Pb₄I₁₃ achieved a PCE of 11.77%, significantly outperforming the 9.18% obtained with PEA-based counterparts. In addition to higher efficiency, the DEA-based devices showed markedly improved operational stability under both mechanical stress and environmental exposure.
The enhanced performance can be attributed to the combined effects of improved crystallinity, larger grain domains, and more favorable energy level alignment introduced by the DEA spacer. These factors collectively enable more efficient carrier extraction while maintaining the intrinsic stability advantages of 2D perovskite structures.
This work highlights spacer cation engineering as a critical lever for advancing flexible perovskite photovoltaics, with DEA⁺ emerging as a promising candidate for achieving both high efficiency and mechanical robustness in next-generation large-area devices.
