Performance enhancement in up-conversion nanoparticle-embedded perovskite solar cells by harvesting near-infrared sunlight

The employment of up-conversion materials in perovskite solar cells (PSCs) provides an intriguing strategy to extend the spectral absorption from the visible to the near infrared (NIR) regions and thus improves device performance. Here, we synthesized an effective up-conversion nanoparticle (UCNP) material, namely NaYF4:Yb3+,Tm3+, which transformed NIR photons to visible and even to UV emissions. For the first time, the UCNPs were incorporated into PSCs by adopting a double-layer structure that consisted of a bottom layer and a top layer of UCNPs, which were located next to the front (FTO) and rear (Au) electrodes, respectively. Importantly, the UCNP-incorporated PSCs achieved a higher power conversion efficiency (PCE) of 18.2% with a higher long-term device stability, in comparison with a PCE of 15.8% from the UCNP-free PSCs. Besides the contribution of additional photocurrent generation via NIR photon up-conversion of the UCNPs, atomic force microscopy and time-resolved photoluminescence spectra measurements revealed that the top and bottom layers of UCNPs also played important roles in the film morphology and charge dynamic behaviors respectively, and all of these features led to performance enhancement.