The authors report the first mesoscopic CH3NH3PbI3/TiO2 heterojunction solar cell, where CH3NH3PbI3 nanoparticles act as both light harvesters and hole conductors, eliminating the need for an additional hole conductor. The device was fabricated by depositing CH3NH3PbI3 nanoparticles on a 400 nm thick TiO2 nanosheet film and covering it with an Au film as a back contact. The solar cell demonstrated impressive photovoltaic performance, achieving a short-circuit photocurrent (Jsc) of 16.1 mA/cm², an open-circuit photovoltage (Voc) of 0.631 V, and a fill factor (FF) of 0.57, corresponding to a power conversion efficiency (PCE) of 5.5% under standard AM 1.5 solar light intensity. At a lower light intensity of 100 W/m², the PCE increased to 7.3%. This simple, solution-processed heterojunction solar cell opens new avenues for the development of low-cost, high-efficiency solar cells.The authors report the first mesoscopic CH3NH3PbI3/TiO2 heterojunction solar cell, where CH3NH3PbI3 nanoparticles act as both light harvesters and hole conductors, eliminating the need for an additional hole conductor. The device was fabricated by depositing CH3NH3PbI3 nanoparticles on a 400 nm thick TiO2 nanosheet film and covering it with an Au film as a back contact. The solar cell demonstrated impressive photovoltaic performance, achieving a short-circuit photocurrent (Jsc) of 16.1 mA/cm², an open-circuit photovoltage (Voc) of 0.631 V, and a fill factor (FF) of 0.57, corresponding to a power conversion efficiency (PCE) of 5.5% under standard AM 1.5 solar light intensity. At a lower light intensity of 100 W/m², the PCE increased to 7.3%. This simple, solution-processed heterojunction solar cell opens new avenues for the development of low-cost, high-efficiency solar cells.