Tetrabutylammonium Hydroxide-Functionalized Ti3C2T x MXene for Significantly Improving the Photovoltaic Performance of Perovskite Solar Cells

An appropriate electron transport layer (ETL) or cathode buffer layer (CBL) is critical for high-performance perovskite solar cells (PVSCs). In this work, tetrabutylammonium hydroxide (TBAOH)-functionalized Ti3C2T x MXene (TBAOH-Ti3C2T x ) is developed to improve the photovoltaic performance of PVSCs. TBAOH-Ti3C2T x is synthesized by HF etching and then TBAOH intercalation, and TBAOH can effectively attach to the Ti3C2T x surface during the intercalation process. In hole transport material (HTM)-free carbon-based PVSCs with the structure of ITO/ETL/MAPbI3/carbon, the SnO2 doped by TBAOH-Ti3C2T x (SnO2:TBAOH-Ti3C2T x ) as ETL shows decreased WF and increased conductivity and improves the growth of the perovskite film with a larger grain and significantly reduced defects, which synergistically facilitate charge transport and extraction and reduce charge recombination. The HTM-free carbon-based PVSC with SnO2:TBAOH-Ti3C2T x ETL exhibits a significantly higher PCE of 14.93% with enhanced device stability compared to the control device with pristine SnO2 ETL (11.95%) and also outperforms most of the HTM-free carbon-based PVSCs with MAPbI3 perovskite reported so far. In traditional inverted PVSCs with the structure of ITO/PTAA/MAPbI3/PCBM/CBL/Ag, the TBAOH-Ti3C2T x is utilized as a CBL to significantly enhance device performance with a high PCE of 21.16%, which is obviously superior than that (16.26%) of the control device without CBL. The impressive results indicate that tetrabutylammonium hydroxide-functionalized Ti3C2T x MXene possesses great application potential in different functional layers for high-performance PVSCs.