Surface Modified Cerium Oxide Nanoparticles For Inorganic Electron Transport Layer In Perovskite Solar Cells

The solar market ushered in the dawn of organic-inorganic perovskite solar cells?PVSCs?with their rapidly increasing power conversion efficiency?PCE?and simple fabrication processes.Currently,the new efficiency record has reached 22.1%,comparable to that of the commercialized PV technologies developed for decades,such as multi-crystalline Si,CIGS and CdTe thin film solar cells.It is very possible that PVSCs would one day step over the threshold of marketization,share or even overturn the current PV market dominated by crystalline-Si solar cells.However,stability issue and high material cost hamper its sustainable development.Interface engineering on charge transport layers?CTLs?is one of the most efficient approaches to improve the cell stability of PVSCs with accessible inorganic charge transport materials?CTMs?.Major inorganic CTMs are always mobilized and conductive,but poor dispersion and bad film quality stuned its application in PVSCs.Here,we proposed a surface modification process for cerium oxide nanoparticles?NPs?which simply synthesized by mature solvothermal technique,and thin film based on these NPs of high quality.In this paper,we employed surface modified CeO₂ as electron transport material?ETM?in p-i-n inverted planar PVSC to obtain improvement of stability and high performance.It is expected that this study set up important experimental and theoretical basis for the development of stabilized PVSCs with high efficiency and low cost.The main results and conclusion of this paper are as follows:Firstly,CeO₂ NPs wrapped with oleic acid were synthesized through a liquid-solid-liquid phase transfer synthetic strategy.Ligand exchange surface modification process then applied on these NPs,achieving a highly conductivity(10^-4 S/cm)of CeO₂ film.Especially,these materials were bipolar with their surface ligands,acetylacetone,which can form nano-ink by easily dispersed into methanol or chlorobenzene.The roughness of compact CeO₂ thin layer prepared through low-temperature solution process is 0.257 nm,it is soft enough to make it possible coating on fragile perovskite what can be degraded when exposed to oxygen and water easily.Secondly,given the high driving force of charge transport and suitable energy level,p-i-n inverted planar PSVCs based on PCBM/CeO₂ bilayer electron transport layer?ETL?were demonstrated with its improved stability and performance.By a drop-casting method,CeO₂nano-ink formed ETL cooperated with PCBM,achieved an aggressive PCE of 18.69%and long-term stability.Unencapsulated device maintained almost 90%of their original efficiency under continuous monitoring at its maximum power point in the ambient air for 200 hours and without significant degradation after being kept in N₂ glovebox.Moreover,all-metal-oxide charge transport layers based PVSCs achieved a promising efficiency of 14.82%.This demonstrates a great progress for apply cheap and stable inorganic nanocrystals on photovoltaic devices.