Flexible perovskite solar cells (PSCs) have attracted extensive interest as the next-generation photovoltaic technology. However, their commercialization has been impeded by undesirable reliability with respect to long-term operational stability and mechanical endurance, which mostly originates from defects that aggregate at layer interfaces in typical PSCs. The charge accumulation due to the imperfect electronic contact at the electron-transport layer (ETL)/perovskite interface (bottom interface) is more significant than that at the perovskite/hole-transport layer (HTL) interface.

We posited that a high concentration of defects (specifically deep-level defects) at the bottom interface may contribute to irreversible degradation of flexible PSCs.

 Therefore we explored the goal of more robust interfacial contact between ETL and perovskite layer. We found that using a well-aligned liquid crystal elastomer (LCE) can simultaneously maintain excellent charge collection and minimize charge recombination at the bottom interface. The molecular ordering is instantly locked upon photopolymerization of liquid crystalline diacrylate monomers and dithiol-terminated oligomers. It provides high surface energy and nucleation density, which promote the film densification process (Figure 1).

Uniform charge transfer channels are configured by the molecular ordering interlayer, which not only reduces the non-radiative interfacial recombination but also promotes the photogenerated charge transfer to the electrode. The tDOS, as a function of the defect energy, demonstrates a reduction in trap states for the SnO₂/LCE based device compared with the SnO₂ based device. On account of the same perovskite composition and film architecture, the reduced trap density can be mainly ascribed to the ordered LCE interlayer that results in robust interfacial contact. (Figure 2).

We report particularly high performance and durable flexible PSCs as well as integrated wearable devices using this new strategy (Figure 3). The resultant rigid and flexible PSCs show efficiency up to 23.26% and 22.10%, respectively. The LCE-induced suppression of phase segregation endows the unencapsulated device maintaining >80% of the initial efficiency for 1570 h. Moreover, the aligned elastomer interlayer preserves the configuration integrity with remarkable repeatability and mechanical robustness, which enables the flexible device to retain 86% of its original efficiency after 5000 bending cycles. The reliable solar cell chips are integrated into a wearable haptic device with microneedle-based arrays of sensors to demonstrate a pain sensation system in virtual reality.

This work titled “Wearable perovskite solar cells by aligned liquid crystal elastomers” was published in the latest volume of Nature Communications journal (https://www.nature.com/articles/s41467-023-36938-7).