The elimination of electron transport layers (ETLs) to fabricate ETL-free perovskite solar cells (PSCs) could save manufacturing costs and time. However, compared with PSCs based on the traditional architecture, ETL-free PSCs suffered low efficiency due to the device shunting and large energy barriers for carriers. Herein, a bifunctional interfacial modification material, 3-aminopropyl trimethoxy silane (APS), is selected and in situ grown on a transparent conducting oxide (TCO). On the one hand, the increased hydrophobicity of APS modified indium tin oxide (ITO) could improve the crystal growth of perovskites, resulting in larger grain sizes and reduced surface defects. On the other hand, the APS modification could improve the energy level alignment of ITO and the perovskite, leading to enhanced electron extraction and hole blocking. The PCE of the ETL-free PSCs based on APS modified ITO reached 19.09%, which was over 60% higher than that of ETL-free PSCs based on ITO.