Room Temperature Ionic Liquid Capping Layer for High Efficiency FAPbI3 Perovskite Solar Cells with Long‐Term Stability

TL;DR

A room-temperature ionic liquid is used to improve the efficiency and stability of perovskite solar cells.

Contribution

A new passivation method using BAAc at room temperature enhances FAPbI3 solar cell performance and scalability.

Findings

BAAc RT passivation achieves 24.76% power conversion efficiency in perovskite solar cells.

The BAAc capping layer improves long-term stability with a T80 lifetime of 3500 hours.

BAAc RT enables 20.47% efficiency in large-area perovskite mini-modules.

Abstract

Ionic liquid salts (ILs) are generally recognized as additives in perovskite precursor solutions to enhance the efficiency and stability of solar cells. However, the success of ILs incorporation as additives is highly dependent on the precursor formulation and perovskite crystallization process, posing challenges for industrial‐scale implementation. In this study, a room‐temperature spin‐coated IL, n‐butylamine acetate (BAAc), is identified as an ideal passivation agent for formamidinium lead iodide (FAPbI3) films. Compared with other passivation methods, the room‐temperature BAAc capping layer (BAAc RT) demonstrates more uniform and thorough passivation of surface defects in the FAPbI3 perovskite. Additionally, it provides better energy level alignment for hole extraction. As a result, the champion n–i–p perovskite solar cell with a BAAc capping layer exhibits a power conversion efficiency (PCE) of 24.76%, with an open‐circuit voltage (Voc) of 1.19 V, and a Voc loss of ≈330 mV. The PCE of the perovskite mini‐module with BAAc RT reaches 20.47%, showcasing the effectiveness and viability of this method for manufacturing large‐area perovskite solar cells. Moreover, the BAAc passivation layer also improves the long‐term stability of unencapsulated FAPbI3 perovskite solar cells, enabling a T80 lifetime of  3500 h when stored at 35% relative humidity at room temperature in an air atmosphere.

In this study, a room‐temperature spin‐coated IL, n‐butylamine acetate (BAAc), is identified as an ideal passivation agent for formamidinium lead iodide (FAPbI3) films. The PCE of the devices treated by BAAc RT achieves 24.76%, with a Voc value reaching as high as 1.19 V.

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