Accelerated Degradation Due to Weakened Adhesion from Li-TFSI Additives in Perovskite Solar Cells

Abstract

Reliable integration of organometallic halide perovskite in photovoltaic devices is critically limited by its low stability in humid environments. Furthermore, additives to increase the mobility in the hole transport material (HTM) have deliquescence and hygroscopic properties, which attract water molecules and result in accelerated degradation of the perovskite devices. In this study, a double cantilever beam (DCB) test is used to investigate the effects of additives in the HTM layer on the perovskite layer through neatly delaminating the interface between the perovskite and HTM layers. Using the DCB test, the bottom surface of the HTM layers is directly observed, and it is found that the additives are accumulated at the bottom along the thickness (i.e., through-plane direction) of the films. It is also found that the additives significantly decrease the adhesion at the interface between the perovskite and HTM layers by more than 60% through hardening the HTM films. Finally, the adhesion-based degradation mechanism of perovskite devices according to the existence of additives is proposed for humid environments.

Short‐Term Stability of Perovskite Solar Cells Affected by In Situ Interface Modification

“…Therefore, we suppose that the additives tBP and acetonitrile (ACN) may play important roles in this PCE transformation. This hypothesis based on our experiments is distinct from previously accepted opinions …”

“…However, it has previously been argued that tBP corrode perovskite within the cells, thus causing a great threat to long‐term stability . In addition, many reports have approved that the reactivity of hygroscopic lithium salts is detrimental to the chemical stability of the perovskite . All the above are considered to contribute to degraded performance and result in the long‐term instability of PSCs.…”

Perovskite Solar Cells: From the Laboratory to the Assembly Line

“…The highest performance HTMs still require additiveso re lse perform poorly.A dditives,h owever,b ring their own set of disadvantages, most notably they cause degradation of the perovskite layer. [71][72][73][74] Thus, removinga dditives has becomea n important direction fori mproving the long-term stabilityo f PSCs. Frequently there is at rade-off between high performance and stability.…”

Hole Transport Materials in Conventional Structural (n–i–p) Perovskite Solar Cells: From Past to the Future

“…However, such materials have hygroscopic and deliquescent properties that lead to HTL demolition, perovskite degradation, and short device lifespan. A few reports have investigated the adverse role of dopants . LiTFSI has deliquescence defined as the ability to absorb moisture in air, which is necessarily harmful to perovskite or spiro‐OMeTAD or both .…”

“…LiTFSI has deliquescence defined as the ability to absorb moisture in air, which is necessarily harmful to perovskite or spiro‐OMeTAD or both . In addition, LiTFSI gradually decreases adhesion at the interface between the perovskite layer and the HTL . tBP slowly and gradually evaporates because of its high boiling point (196 °C) and reacts with the perovskite layer, forming a new complex with PbI 2 , which quickly deteriorates the device performances .…”