Amino acid modified Ti3C2Tx as electron transport layers for high-performance organic solar cells

The Ti3C2Tx, as a typical representative of the MXene family, has attracted much attention due to excellent properties in terms of transmittance, conductivity, tunable work function (WF), and low temperature solution processability. However, the work function that needs to be adjusted and a large number of crystal defects in Ti3C2Tx greatly restrict its use in electronic devices. Herein, Ti3C2Tx is modified with amino acids to modulate WF of Ti3C2Tx and passivate its defect sites, thereby improving the electrical properties of Ti3C2Tx and enhancing the performance of organic solar cells (OSCs). Amino acids interact with Ti3C2Tx by charge transfer and forming a surface dipole on the surface, which reduces the WF of Ti3C2Tx. Moreover, -NH2 of amino acids passivates the negatively charged Ti vacancies in Ti3C2Tx, while -COOH of amino acids passivates the positively charged C vacancies, increasing the conductivity of Ti3C2Tx. Consequently, the OSCs with amino acid-modified Ti3C2Tx-based as new electron transport layer (ETL) exhibit more than 18% of power conversion efficiency (PCE) and good device stability. The work shows OSCs with high performance can be fabricated by using environmental-friendly amino acids, which inspires researchers to seek ideas for fabricating efficient devices from natural materials.