Abstract
In this work, we report on solution-based p-i-n-type planar-structured CH3NH3PbI3 perovskite photovoltaic (PV) cells, in which precrystallized NiO nanoparticles (NPs) without post-treatment are used to form a hole transport layer (HTL). X-ray diffraction and high-resolution transmission electron microscopy showed the crystallinity of the NPs, and atomic force microscopy and scanning electron microscopy confirmed the uniform surfaces of the resultant NiO thin film and the subsequent perovskite photoactive layer. Compared to the conventional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL, the NiO HTL had excellent energy-level alignment with that of CH3NH3PbI3 and improved electron-blocking capability, as analyzed by photoelectron spectroscopy and diode modeling, resulting in Voc ~0.13 V higher than conventional PEDOT:PSS-based devices. Consequently, a power conversion efficiency (PCE) of 15.4% with a high fill factor (FF, 0.74), short-circuit current density (Jsc, 20.2 mA·cm−2), and open circuit voltage (Voc, 1.04 V) having negligible hysteresis and superior air stability has been achieved.
Highlights
There has been significant improvement in the performance of perovskite-based PV cells since they were first reported[8], when CH3NH3PbI3 was initially used as a visible-light sensitizer in DSSCs on mesoporous TiO2
The Nickel oxide (NiO) NPs utilized in this work to form an hole transport layer (HTL) between the perovskite photoactive layer and the ITO electrode were synthesized by the reduction of Ni(II) acetylacetonate (C10H14NiO4) via the reducing agent borane-triethylamine complex [(C2H5)3NBH3] in oleylamine (C18H37N), which was both the solvent and the surfactant
We found that the quality of the NiO thin film was affected significantly by residual impurities after synthesis; the synthesized NPs underwent extra ethanol rinses to thoroughly remove the residual chemicals for better film quality
Summary
There has been significant improvement in the performance of perovskite-based PV cells since they were first reported[8], when CH3NH3PbI3 was initially used as a visible-light sensitizer in DSSCs on mesoporous (mp) TiO2. Recent reports showed that the hysteretic I-V characteristics in p-i-n-type planar heterojunction perovskite PV cells having indium tin oxide(ITO)/hole transport layer(HTL)/CH3NH3PbI3/PCBM electron transport layer(ETL)/metal electrode structures were suppressed[16,17]. This is beneficial because this structure compensates for the effect of the relatively short hole diffusion length and provides better charge balance, and the PCBM ETL, cast on the photoactive layer, is expected to passivate charge trap states on the surface and grain boundary of the CH3NH3PbI3 perovskite materials[9,16,17]. Quantum efficiency and absorbance were used to analyze the performances of the PV cells
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