Abstracts Category : Other

Optimization of nanoarchitectures for high-performance planar perovskite solar cells [an abstract of entire text]

by Ahmed Esmail Shalan

Perovskite solar cells (PSCs) based on organometal halide light-absorbing materials have attracted enormous research interest for solar cell applications due to their many intriguing optical and electronic features, such as large absorption coefficient, large chargecarrier mobility, long carrier-recombination lifetime and unique defect physics. Since the first report on a solid-state PSC with a (power conversion efficiency) PCE of 9.7% in 2012, and a PCE of 22.1% was certified in 2016. To improve the net PCE value more, it is important to elucidate the essential factors influencing on the PCE. This thesis focused on several element technologies to enhance PCE and the external quantum efficiency (EQE) from the viewpoints of 1) the light-harvesting, and 2) the hole extraction material. These studies were performed in order to give a better understanding and insight into the nanoarchitectures optimization for high-performance PSCs. Although a lot of studies have been done related to PSCs, the EQE values are almost saturated especially in the longer wavelengths. Therefore, it is necessary to find a new way to improve the EQE at longer wavelengths for PSCs. Plasmonics is a highly promising due to its light-harvesting property. In this section, inverted planar PSCs with a p-i-n device configuration of indium-doped tin oxide (ITO)/NiO/CH3NH3PbI3/[6,6]-phenyl-C61-butanoic acid methyl ester (PCBM)/Ag with and without gold nanoislands (Au NIs) were prepared. The results demonstrated that the Au NIs increased the PCE to 5.1%, almost twice that of the samples without Au NIs. This result is due to the excitation of surface plasmons. Furthermore, we observed an enhancement of EQE at wavelengths shorter than the plasmon resonance. It is speculated that the plasmoelectric potential effect may contribute to the enhancement of EQE at the off-resonance region. A hole-extracting layer (HEL) is a key material which affects device performances of PSCs. CoOx is a promising HEL for inverted planar PSCs with a p-i-n device configuration of ITO/CoOx/CH3NH3PbI3/PCBM/Ag. The devices fabricated according to a simple solution procedure showed the best photovoltaic PCE 14.5%, which is significantly superior to those fabricated with traditional HEL such as PEDOT:PSS (12.2%), NiOx (10.2%) and CuOx (9.4%), under the same experimental conditions. Photoluminescence (PL) spectra and the corresponding PL lifetime of perovskite deposited on varied HEL films were measured to obtain the hole-extracting characteristics, for which the hole-extracting times consistent with the trend of their PCE. The reproducibility and endurance of those devices were examined to show the outstanding long-term stability of the devices made of metal oxide HEL, for which the CoOx device still had PCE ~12% for over 1000 h.