Preparation and performance of high-efficient hole-transport-material-free carbon based perovskite solar cells

Carbon based perovskite solar cells (C-PSCs) have attracted much attention because of their high stability and low-cost of production. However, due to the high interfacial resistance and the low energy level matching between perovskite and carbon electrodes, the maximum power conversion efficiency (PCE) is less than that of the metal-based perovskite solar cells. In this paper, a carbon-based perovskite solar cell is fabricated with the device structure of FTO/c-TiO2/m-TiO2/CH3NH3PbI3/Carbon. The perovskite films and carbon based perovskite solar cells are characterized by scanning electron microscope, atomic force microscope, X-ray diffraction (XRD), UV-Vis absorption spectrum, the steady-state spectrum, the time-resolved PL (TRPL) spectrum, and an electrochemical workstation. In addition, the internal mechanism of the efficiency improvement of carbon-based perovskite solar cell is discussed in depth. Then, the rotation speeds of mesoporous TiO2 layer (TiO2 paste diluted by ethanol with mass ratio of 1:4) are 1500, 1600, 1700 and 1800 r/min and the speeds of perovskite layer (CH3NH3I and PbI2 at a 1:1 molar ratio are stirred in a mixture of DMF and DMSO (9:1, v/v)) are 2000, 3000, 4000 and 5000 r/min; When the speed of m-TiO2 layer is 1700 r/min and the speed of perovskite layer is 4000 r/min, the mesoporous TiO2 layer thickness is about 500 nm, Thickness of CH3NH3PbI3 capping layer is about 400 nm. The cooperation of these two layers eventually leads to the high-quality perovskite with enlarged grain size, prolonged photoluminescence lifetime, lowered defect density, increased carrier concentration, and the finally enhanced photovoltaic performance. The device obtains the highest PCE of 11.11% with an open circuit voltage (Voc) of 0.93 V, a current density (Jsc) of 21.75 mA/cm2 and fill factor (FF) of 55%. At the same time, the stability of the carbon-based perovskite solar cell is also studied. The XRD is used for initial perovskite and the perovskite after 15 days to investigate the photo- and humidity stability of the full cells without encapsulation. The device exhibits excellent air stability with only 5% degradation when aged in ambient air at room temperature with 40%-50% humidity without any encapsulation after 15 days, which is better than the metal based perovskite solar cell. Our results open the way for making cost-efficient and stable PSCs toward market deployment.