Inhibited Aggregation of Lithium Salt in Spiro-OMeTAD for Perovskite Solar Cells

Abstract

High-efficiency and stable hole transport materials (HTMs) play an essential role in high-performance planar perovskite solar cells (PSCs). 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobi-fluorene (Spiro-OMeTAD) is often used as HTMs in perovskite solar cells because of its excellent characteristics, such as energy level matching with perovskite, good film-forming ability, and high solubility. However, the accumulation and hydrolysis of the common additive Li-TFSI in Spiro-OMeTAD can cause voids/pinholes in the hole transport layer (HTL), which reduces the efficiency of the PSCs. In order to improve the functional characteristics of HTMs, in this work, we first used CsI as a dopant to modify the HTL and reduce the voids in the HTL. A small amount of CsI is introduced into Spiro-OMeTAD together with Li-TFSI and 4-tert-butylpyridine (TBP). It is found that CsI and TBP formed a complex, which prevented the rapid evaporation of TBP and eliminated some cracks in Spiro-OMeTAD. Moreover, the uniformly dispersed TBP inhibits the agglomeration of Li-TFSI in Spiro-OMeTAD, so that the effective oxidation reaction between Spiro-OMeTAD and air produces Spiro-OMeTAD+ in the oxidation state, thereby increasing the conductivity and adjusting the HTL energy. Correspondingly, the PCE of the planar PSC of the CsI-modified Spiro-OMeTAD is up to 13.31%. In contrast, the PSC without CsI modification showed a poor PCE of 10.01%. More importantly, the PSC of Spiro-OMeTAD treated with CsI has negligible hysteresis and excellent long-term stability. Our work provides a low-cost, simple, and effective method for improving the performance of hole transport materials and perovskite solar cells.

Outstanding Thermal Stability of Perovskite Solar Cells Based on Zn(TFSI)2-Doped Spiro-MeOTAD

“…The weakened role of plasticizer by using Zn­(TFSI) 2 and tBP can be assumed by the weight loss as a function of temperature in Figure . While the pristine spiro-MeOTAD exhibits a single step in weight loss (Figure a), spiro-MeOTAD with LiTFSI and tBP demonstrates discrete decay steps (Figure b), where the residual solvent, mainly composed of tBP, rapidly evaporates at the initial heating stage (<200 °C), − whereas the initial weight loss is significantly inhibited with a gentle slope owing to the strong interaction of tBP in the presence of Zn­(TFSI) 2 (Figure c).…”

Degassing 4-tert-Butylpyridine in the Spiro-MeOTAD Film Improves the Thermal Stability of Perovskite Solar Cells

“…However, the pain point remains because of conductivity loss by the diffusion of lithium cation triggered by the presence of coadditive tBP and aggregation caused by evaporation of tBP. 35 Thus, an effective way together with the factors affecting the thermal stability of the Spiro-MeOTAD−based PSCs should be discovered to enhance the thermal stability of Spiro-MeOTAD. 36 In this work, the effects of the additives in the Spiro-MeOTAD film on the thermal stability of PSCs were systematically explored to unveil the origin of thermal instability of PSCs employing the additive-containing Spiro-MeOTAD film.…”

“…On the perspective of stability, the passivation benefits blocking the migration of ions from perovskite to Spiro-MeOTAD film and suppressing the diffusion of LiTFSI from Spiro-MeOTAD to perovskite, as well as controlling the underlying chemical reaction of tBP with perovskite surface. However, the pain point remains because of conductivity loss by the diffusion of lithium cation triggered by the presence of coadditive tBP and aggregation caused by evaporation of tBP . Thus, an effective way together with the factors affecting the thermal stability of the Spiro-MeOTAD–based PSCs should be discovered to enhance the thermal stability of Spiro-MeOTAD …”

Theoretical analysis of the electrical characteristics of lead‐free formamidinium tin iodide solar cell

“…More recently, Manish et al [13] reported an optimised PCE of 19.08% in FASnI 3 based solar cell device with TiO 2 as the ETL and spiro-OMeTAD as the HTL. Due to low hole mobility and conductivity in spiro-OMeTADs' pristine form [14], as well as self-aggregation when deposited as a thin film, the proposed structure was found to be inactive.…”