2021 Energy Environ. Sci. (IF 38.532), 22.09% PCE Inverted Perovskite! How does hydroxylated NFA work?

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　　Energy & Environmental Science (IF 38.532) recently published a study to explore hydroxylated non-fullerene acceptors (NFA) that could be used in inverted perovskite solar cells and achieved a high efficiency of 22.09%. In the past decade, organic-inorganic metal halide perovskite solar cells (PSC) have led to extensive research, and power conversion efficiency (PCE) has also been continuously improved. Compared with the traditional n-i-p structure PSC, the inverted p-i-n structure PSC (i-PSC) shows negligible hysteresis and can be used to construct tandem solar cells. However, due to the non-radiative recombination of the defect state and the energy mismatch of the electron transport layer, the power conversion efficiency (PCE) of i-PSC still lags behind that of traditional batteries.

　　In this study, in order to reduce defects and improve electron transport at the same time, the research team used hydroxylated non-fullerene receptors (called IT-DOH) to modify the interface between the perovskite and the electron transport layer (ETL). IT-DOH molecules were mainly distributed at the grain boundaries and acted in three ways:

First, compared with the reference molecule ITIC. In addition to the -CN and -C=O groups, the additional -OH could be used with Pb²⁺ to further passivate the defects of the perovskite film and inhibit non-radiative recombination more effectively.

Second, the LUMO energy level of ITDOH formed a cascade energy level arrangement and promotes electron extraction.

Third, due to the elongation of the conjugated surface caused by the hydrogen bond interaction between molecules, the IT-DOH molecule exhibited a long-range-ordered molecular arrangement and frontal orientation, which facilitated the transfer of electrons from the perovskite to the ETL.

　　The current density-voltage (J−V) measurement, forward scan and reverse scan were carried out through the Enlitech’s solar simulator, and the external quantum efficiency (EQE) test was carried out with the QE-R quantum efficiency measurement system of Enlitech. The results of the study found that the i-PSC processed by IT-DOH achieved a PCE of 22.09%, which is the highest value among the published papers on NFA i-PSC. This study also confirmed that the hydroxylation of NFA molecules is very important for reducing defects and improving electron extraction/transport.

　　In addition to the EQE (External Quantum Efficiency) spectrum analysis of solar cells, the Quantum Efficiency Measurement System of Enlitech also provides J_sc (short-circuit current density) comparison for the short-circuit current of solar cells under the solar simulator to prove the authenticity of the experiment. The solar simulator and KA-6000 software of Enlitech also provide monitoring of the short-circuit current over time to prove the stability of the solar cell!