Efficient Perovskite Solar Cells Based on Tin Oxide Nanocrystals with Difunctional Modification

Tin oxide (SnO2) nanocrystals-based electron transport layer (ETL) has been widely used in perovskite solar cells due to its high charge mobility and suitable energy band alignment with perovskite, but the high surface trap density of SnO2 nanocrystals harms the electron transfer and collection within device. Here, an effective method to achieve a low trap density and high electron mobility ETL based on SnO2 nanocrystals by devising a difunctional additive of potassium trifluoroacetate (KTFA) is proposed. KTFA is added to the SnO2 nanocrystals solution, in which trifluoroacetate ions could effectively passivate the oxygen vacancies (O-V) in SnO2 nanocrystals through binding of TFA(-) and Sn4+, thus reducing the traps of SnO2 nanocrystals to boost the electrons collection in the solar cell. Furthermore, the conduction band of SnO2 nanocrystals is shifted up by surface modification to close to that of perovskite, which facilitates electrons transfer because of the decreased energy barrier between ETL and perovskite layer. Benefiting from the decreased trap density and energy barrier, the perovskite solar cells exhibit a power conversion efficiency of 21.73% with negligible hysteresis.

Automated summary

In this study, an effective method to achieve a low trap density and high electron mobility electron transport layer (ETL) based on SnO2 nanocrystals is proposed. The addition of potassium trifluoroacetate (KTFA) is able to passivate the oxygen vacancies in SnO2 nanocrystals, reducing traps and boosting electron collection. Furthermore, surface modification shifts the conduction band of SnO2 nanocrystals close to that of perovskite, facilitating electron transfer. As a result, the perovskite solar cells exhibit high efficiency and negligible hysteresis.