Benefits of surface engineered silicon quantum dots in formamidinium lead iodide perovskite solar cells

Hybrid quantum dot (QD) solar cells based on solution-processed blends of perovskites with Si QDs might be a potential candidate toward practical use of its outstanding optoelectronic properties. On the other hand, to overcome the stability bottleneck of perovskites we avoid using methylammonium (MA) ions and instead favor the more thermally stable formamidinium (FA) cation. In this contribution we present details on the synthesis and wide characterizations (e.g. energy bands evaluation, elemental content analysis, etc.) of FA lead iodide (FAPbI3) stable thin films and single junction FAPbI3 solar cells with efficiencies exceeding > 20%. We show that FAPbI3 with the energy gap 1.54 eV considerably enhances the short-circuit current density (JSC) and does not compromise the VOC, whereby VOC exceeds >1.1 eV. We furthermore show that the integration of surface engineered (SE) Si quantum dots into the FAPbI3 absorber does not significantly change the material properties such as energy band gap, while exhibiting superior solar cell properties over long time durations. We observed superior properties of solar cells made from SE Si-QDs in FAPbI3 over long time durations (5 months stored in a dry box between I-V measurements) compared to FAPbI3 without SE Si-QDs. Typical performance for the reference FAPbI3 solar cell (JSC = 20.6 mA/cm2, VOC =0.98 V, FF =67%, eta=13.7 %) and that with SE Si-QDs (JSC = 22.5 mA/cm2, VOC =1.05 V, FF =65%, eta=15.4 %) after 5 months. The external quantum efficiency (EQE) of SE Si-QDs in FAPbI3 cells remains superior after 5 months and the evaluated JSC roughly correspond to that from the I-V curves.