Experimental and SCAPS simulated formamidinium perovskite solar cells: A comparison of device performance

In this study, experimental photovoltaic performance and their numerical SCAPS-1D simulations are compared for methylammonium-free perovskite solar devices based on the formamidinium organic cation. Experimentally, it is established that the incorporation of small amounts of cesium (Cs+) and bromide (Br-) into HC(NH2)2PbI3(FAPI) stabilizes the optically active α-FAPbI3 black phase, and boost the power conversion efficiency (PCE) of associated devices from 4 to 15% under standard illumination. The effect of series and shunt resistances (Rseries & Rshunt) were theoretically evaluated and discussed by modeling the electrical characteristics of the cell as a function of active layer composition, using the SCAPS-1D software. Ideal devices built without these parasitic resistances do not match the experimental trends, although they reflect the influence of bandgap edge on the photocurrent generation. Feeding the experimental Rseries and Rshunt values to SCAPS allows us to interpret the main limitations to the device current-voltage characteristics. The instability of the pure FAPI phase is responsible for the drastic deterioration in Rseries and Rshunt, ultimately influencing the fill factor. Our data clearly confirm the beneficial effect of mixed cation and mixed halides on device operation.