The development of efficient photodetectors (PDs) for ultraviolet (UV) light is of great importance for many applications. In the present paper, we propose a novel approach for boosting the performances of self-powered PDs. Visible-blind UV-A PDs have been built by combining a mesoporous TiO2 layer with a Spiro-OMeTAD layer. The nanostructured heterointerface has been engineered by inserting a self-assembled layer of organic modifiers. By choosing the 4-nitrobenzoic acid (NBA), the responsivity has been boosted by 70% compared to the pristine devices. It achieved 64 mA/W at 0 V bias, 380 nm and 1 mW.cm-2. The PD displayed a very high sensitivity (> 10 4), a fast response time (< 3ms), a high stability and repeatability. 4-chlorobenzoic acid, 4-methoxy benzoic acid, 4-nitro benzoic acid and β-alanine surface modifier have been studied by a combined experimental and theoretical approach. Their dipole moment has been calculated. Their presence induces a step in the 2 vacuum energy and the formed dipole field dramatically affects the charge transfer and then the photocurrent/photoresponse of the device. The higher responsivity of the NBA-modified PD has been thus explained by the better and faster electron charge transfer towards the electrical contact on TiO2.