Stability in photoluminescence and photovoltaic properties of formamidinium lead iodide quantum dots

Formamidinium lead iodide (FAPI) thin films in the perovskite crystalline phase have piqued interest for single-junction solar cells due to their optimal bandgap, long photocarrier lifetime, and intrinsic structural stability. However, trap states on the surface and within the lattice impede the performance and stability of FAPI bulk crystalline film cells. Strategies such as film crystallization, deposition optimization, precursor engineering, and interface property tailoring aim to overcome these limitations. One approach involves forming FAPI quantum dots (QDs). By reducing the size, we achieve better quality and stable alpha-phase FAPI on a nanometer scale. In this contribution, we report synthesizing of alpha-phase FAPI QDs with a mean size distribution of 20 nm. These QDs exhibit a narrow photoluminescence emission peak at 1.61 eV and higher absolute quantum yields ranging from 70% to 86%. Compared to bulk FAPI with a 1.54 eV gap, a blue shift is observed due to the quantum confinement effect. However, achieving degradation-free perovskite solar cells under prolonged light soaking remains a challenge. Furthermore, we investigate the stability of FAPI bulk and QDS films in a humid chamber and after exposure to AM1.5G light in a humid setting (RH ~ 30%, T ~ 28°C). Our approach allows us to form homogeneously dispersed films of quantum dots with thicknesses of several hundred nanometers. These films are studied for photoluminescence and photovoltaic properties. Prototype solar cells incorporating synthesized FAPI QDs showed a power conversion efficiency of around 8%. These findings indicate considerably more stability in photoluminescence and photovoltaic properties of FAPI QDs for enhanced light-soaking stability compared to bulk FAPI films.