Chang-Ryul Lee

Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%.

We report on solid-state mesoscopic heterojunction solar cells employing nanoparticles (NPs) of methyl ammonium lead iodide (CH3NH3)PbI3 as light harvesters. The perovskite NPs were produced by reaction of methylammonium iodide with PbI2 and deposited onto a submicron-thick mesoscopic TiO2 film, whose pores were infiltrated with the hole-conductor spiro-MeOTAD. Illumination with standard AM-1.5 sunlight generated large photocurrents (JSC) exceeding 17 mA/cm2, an open circuit photovoltage (VOC) of 0.888 V and a fill factor (FF) of 0.62 yielding a power conversion efficiency (PCE) of 9.7%, the highest reported to date for such cells. Femto second laser studies combined with photo-induced absorption measurements showed charge separation to proceed via hole injection from the excited (CH3NH3)PbI3 NPs into the spiro-MeOTAD followed by electron transfer to the mesoscopic TiO2 film. The use of a solid hole conductor dramatically improved the device stability compared to (CH3NH3)PbI3 -sensitized liquid junction cells.

Pseudo first-order adsorption kinetics of N719 dye on TiO2 surface.

We have investigated the adsorption kinetics of Ru-based N719 dye on TiO(2) surface in dye-sensitized solar cell using 0.5 mM and 5 mM dye solutions. The amount of adsorbed dye on TiO(2) surface of ca. 5 μm-thick film was measured as a function of immersion (adsorption) time. The amount of adsorbed dye increases with increasing the adsorption time and keeps constant after saturation. Completion of dye adsorption is found to be more than 5 times faster in 5 mM than in 0.5 mM. Since the change of dye concentration is negligible compared to that of number of TiO(2) adsorption site, reaction order and rate constant can be estimated from a pseudo reaction. Among the zeroth-, first-, and second-order simulation, the observed data follow first order reaction for both 0.5 mM and 5 mM cases. The rate constant is estimated to be 0.504 min(-1) for 5 mM and 0.094 min(-1) for 0.5 mM, which indicates that completion of dye adsorption is about 5 times shorter in 5 mM than in 0.5 mM. This is consistent with the observed adsorption time difference. Except for the difference in adsorption kinetics, best cell efficiency is similar regardless of dye solution concentration.

Hierarchical SnO2 Nanoparticle-ZnO Nanorod Photoanode for Improving Transport and Life Time of Photoinjected Electrons in Dye-Sensitized Solar Cell

A hierarchical photoanode comprising a SnO(2) nanoparticle underlayer and a ZnO nanorod overlayer was prepared and its photovoltaic performance was compared to photoanodes consisting of SnO(2) nanoparticle only and ZnO nanorod only. The photoanode layer thickness was adjusted to about 7.6 μm to eliminate thickness effect. Ruthenium complex, coded N719, was used as a sensitizer. The photoanode composed of ZnO nanorod only showed a power conversion efficiency (PCE) as low as 0.54% with a short-circuit photocurrent density (J(SC)) of 2.04 mA/cm(2) and an open-circuit voltage (V(OC)) of 500 mV. The photoanode with SnO(2) nanoparticle only exhibited higher PCE (1.24%) because of higher J(SC) (6.64 mA/cm(2)), whereas V(OC) (340 mV) was lower than ZnO nanorod. Compared to SnO(2) nanoparticle and ZnO nanorod films, the bilayer structured film demonstrated much higher PCE (2.62%) because of both higher J(SC) (7.35 mA/cm(2)) and V(OC) (660 mV). Introduction of ZnO nanorod on the SnO(2) nanoparticle layer improved significantly electron transport and lifetime compared to the SnO(2) only film. One Order of magnitude slower charge recombination rate for the bilayer film than for the SnO(2) film was mainly responsible for the improved efficiency.