Solution-processable Ti3C2Tx nanosheets as an efficient hole transport layer for high-performance and stable polymer solar cells

MXenes, a newly interesting family of two-dimensional (2D) materials, have recently attracted wide attention owing to their unique photoelectric properties. In this study, 2D Ti3C2Tx, a classic representative of the MXene family, is fabricated and functioned as a hole transport layer (HTL) in polymer solar cells (PSCs) due to its features of outstanding metallic conductivity, excellent optical transparency, suitable work function, and superior mechanical properties. The Ti3C2Tx nanosheets deposited from neutral solutions are incorporated between the photoactive layer and the anode electrode as HTLs to facilitate charge transport and collection characteristics in PSCs. The results show that the Ti3C2Tx film possesses good light transmission and high conductivity. The photovoltaic characteristics of the Ti3C2Tx-based devices are systematically investigated. It is demonstrated that the incorporation of Ti3C2Tx as a HTL endows PSCs with superior charge extraction capability, exhibiting a significantly higher power conversion efficiency (PCE) of 10.53% than that of the only ITO-based device (4.21%) with PBDB-T as the donor and ITIC as the acceptor. Such photovoltaic performance also outperforms that of the state-of-the-art PEDOT:PSS-based devices (10.11%). Furthermore, the Ti3C2Tx-based device also shows better long-term stability under atmospheric conditions without any encapsulation than the PEDOT:PSS devices, which indicates that the 2D Ti3C2Tx material possesses great potential in PSCs.