Multi-Influences of Ionic Migration on Illumination-Dependent Electrical Performances of Inverted Perovskite Solar Cells

ZnO films are employed as the electron transport layers for perovskite solar cells. Such a device exhibits an ultralong time increase in <i>V</i>_oc (∼100 s) and <i>J</i>_sc (∼1000 s) and a weakening hysteresis under continuous illumination. Besides, a slow (∼20 s) <i>V</i>_oc decay when illumination is switched off is also observed. The electrical measurements performed under illumination and under voltage bias before being illuminated, suggest the influences of ionic accumulation/redistribution in causing above phenomena. Ionic accumulation happening in dark and ionic redistribution under illumination lead to band bending which affects the excitons separation and carrier extraction. These can account for the ultralong time increase in <i>V</i>_oc and <i>J</i>_sc as well as the slow <i>V</i>_oc decay. Also, the time-dependent photocurrent response under stepwise scan proves the presence of a capacitive effect in the device which can be dramatically reduced by the ionic redistribution under illumination. The ionic redistribution is also an important reason for the weakening hysteresis

Enhanced Photoluminescence and Thermal Properties of Size Mismatch in Sr_{2.97–<i>x</i>–<i>y</i>}Eu_0.03Mg_<i>x</i>Ba_<i>y</i>SiO₅ for High-Power White Light-Emitting Diodes

In this Study, Mg²⁺ and Ba²⁺ act to enhance the maximum emission of Sr_2.97SiO₅:0.03Eu²⁺ significantly and redshift the emission band to the orange-red region in Sr_{2.97–<i>x</i>–<i>y</i>}Mg_<i>x</i>Ba_<i>y</i>SiO₅:0.03Eu²⁺. Size mismatch between the host and the doped cations tunes the photoluminescence spectra shift systematically. A slight blue shift when increasing the amount of Mg²⁺ occurs in the Sr_{2.97–<i>x</i>}Eu_0.03Mg_<i>x</i>SiO₅ lattices, and a rapid red shift occurs when Ba²⁺ is codoped in the Sr_{2.57–<i>y</i>}Eu_0.03Mg_0.4Ba_<i>y</i>SiO₅ lattices. The emission spectra were tuned from 585 to 601 nm by changing the concentration of Ba²⁺. Accordingly, we propose the underlying mechanisms of the changes in the photoluminescence properties by adjusting the cation composition of phosphors. The influence of the size mismatch on the thermal quenching is also observed. This mechanism could be widely applied to oxide materials and could be useful in tuning the photoluminescence properties, which are sensitive to local coordination environment. The emission bands of Sr_{2.97–<i>x</i>–<i>y</i>}Eu_0.03Mg_<i>x</i>Ba_<i>y</i>SiO₅ show the blue shift with increasing temperature, which could be described in terms of back tunneling of the excited electrons from the low-energy excited state to the high-energy excited state. Thus, the Sr_{2.97–<i>x</i>–<i>y</i>}Eu_0.03Mg_<i>x</i>Ba_<i>y</i>SiO₅ phosphors could have potential applications in the daylight LEDs or warm white LEDs

Highly Efficient Flexible Perovskite Solar Cells Using Solution-Derived NiO_<i>x</i> Hole Contacts

A solution-derived NiO_<i>x</i> film was employed as the hole contact of a flexible organic–inorganic hybrid perovskite solar cell. The NiO_<i>x</i> film, which was spin coated from presynthesized NiO_<i>x</i> nanoparticles solution, can extract holes and block electrons efficiently, without any other post-treatments. An optimal power conversion efficiency (PCE) of 16.47% was demonstrated in the NiO_<i>x</i>-based perovskite solar cell on an ITO-glass substrate, which is much higher than that of the perovskite solar cells using high temperature-derived NiO_<i>x</i> film contacts. The low-temperature deposition process made the NiO_<i>x</i> films suitable for flexible devices. NiO_<i>x</i>-based flexible perovskite solar cells were fabricated on ITO-PEN substrates, and a preliminary PCE of 13.43% was achieved

Amino Acid Double-Passivation-Enhanced Quantum Dot Coupling for High-Efficiency FAPbI₃ Perovskite Quantum Dot Solar Cells

Formamidinium lead triiodide (FAPbI3) perovskite quantum dot has outstanding durability, reasonable carrier lifetime, and long carrier diffusion length for a new generation of highly efficient solar cells. However, ligand engineering is a dilemma because of the highly ionized and dynamic characteristics of quantum dots. To circumvent this issue, herein, we employed a mild solution-phase ligand-exchange approach through adding short-chain amino acids that contain amino and carboxyl groups to modify quantum dots and passivate their surface defects during the purification process. As a result, the photoelectric conversion efficiency of FAPbI3 perovskite quantum dot solar cells (PQDSCs) increased from 11.23 to 12.97% with an open-circuit voltage of 1.09 V, a short-circuit current density of 16.37 mA cm–2, and a filling factor of 72.13%. Furthermore, the stability of the device modified by amino acids retains over 80% of the initial efficiency upon being exposed to 20–30% relative humidity for 240 h of aging treatment. This work may offer an innovative concept and approach for surface ligand treatment to improve the photovoltaic performance of PQDSCs toward large-scale manufacture