MXene-Based Tailoring of Carrier Dynamics, Defect Passivation, and Interfacial Band Alignment for Efficient Planar p–i–n Perovskite Solar Cells

Defect passivation and tailoring of perovskite–charge transport layer interfaces are critical strategies to minimize the recombination losses and improve the power conversion efficiency (PCE) in perovskite solar cells (PSCs). Herein, we use titanium carbide MXene (Ti3C2Tx) to tailor the electronic properties of the electron transport layer (ETL) and ETL/perovskite interface in inverted (p–i–n) PSCs and correlate them to the observed PCE. MXene doping in a [6,6]-phenyl-C61-butyric acid methyl ester (M-PC61BM)-based ETL results in an improved electrical conductivity and ETL/perovskite interface band alignment. A red shift in the Ag(2) peak in the Raman spectrum and a localized upshift of the Fermi level calculated using scanning Kelvin probe force microscopy (SKPFM) confirm the n-doping of PC61BM. Consequently, PSC devices with M-PC61BM as the ETL show a higher PCE of 18% than PC61BM ETL-based control devices (PCE = 15.2%). Importantly, our study proves that the improvement in the open-circuit voltage (VOC) and fill factor (FF) depends on how MXene is integrated into the PSC, i.e., as a dopant in the PC61BM ETL, an interfacial layer between the perovskite and ETL, or a standalone ETL. Through comprehensive photoluminescence, electrochemical impedance spectroscopy, space-charge limited current, and scanning Kelvin probe force microscopy-based analyses, we establish that the introduction of MXene in PSCs has multiple benefits, including improvement in carrier transport, passivation and trap state reduction, and better interfacial energy alignment. Further, we unravel the most prominent factor influencing device performance in each mode of MXene introduction. Hence, the study reinforces the potential of Ti3C2Tx MXene as a versatile material for high-performance electronic and optoelectronic devices.