The degradation of perovskite precursor

Perovskite solar cells(PSCs)are taking a leading position in thin-film optoelectronic devices due to their excellent optical,physical and electrical properties[1-4].Nevertheless,the stability issue of metal halide perovskite precursor solution severely retards the future industrialization of PSCs[5-7].In stoichiometry,slight solution composition change will induce severe degradation of device performance.

Self-assembled monolayers enhance the performance of oxide thin-film transistors

Thin-film transistors(TFTs)based on oxide semiconductors have gained a lot of attention in applications such as displays and sensors particularly in recent years due to the advantages of oxide semiconductors like high mobility,good uniformity over large area and low deposition temperature[1−4].However,the defects/traps at dielectric/channel interface and top surface of oxide TFTs might dramatically degrade device performance including current on/off ratio,mobility and most importantly stability[5,6],making it quite urgent to systematically make effective interface engineering to improve TFT performance.

Dimethylammonium cation stabilizes all-inorganic perovskite solar cells

Facing the poor environmental stability of traditional methylammonium or formamidinium-based lead halide per-ovskites,scientists turn their attention to inorganic lead hal-ide perovskites(ILHPs)with narrow bandgaps,excellent thermal stability and reduced ion migration compared to their organic/inorganic counterparts[1−4].Up to now,the PCEs for ILHP solar cells exceed 21%[5].Especially,the preferred black ILHP(e.g.CsPbI3)with the smallest bandgap of~1.7 eV and single-halide composition for avoiding phase separation is crucial for high-performance single-junction solar cells and can be applied in tandem devices as the top cells[6,7].However,small Cs+(167 pm)in CsPbI3 with a tolerance factor close to 0.8 is unsuitable for the 3D PbI3-framework[8].The mis-matched size of cations will induce lattice strain and the per-ovskite spontaneously transforms to undesired non-photoact-ive yellow phase(δ-phase,like NH4CdCl3)(Fig.1(a))[9,10].There-fore,improving lattice symmetry and reducing lattice strain are the strategies for inhibiting the phase transition of ILHPs.

Doping organic hole-transport materials for high-performance perovskite solar cells

Single-junction and tandem perovskite solar cells(PSCs)have achieved impressive power conversion efficiencies(PCEs)of 25.7%and 31.3%,respectively,which makes it to be one of next-generation photovoltaic technologies[1−9].Inter-face engineering[3,5,10−12],composition engineering[13]and ad-ditive engineering[7,14,15]have made remarkable contribu-tions to efficiency enhancement.Compared with efficiency,the long-term operational stability of PSCs jogs along,which is far from the requirements of commercialization.Currently,almost all regular n-i-p PSCs were accomplished with classic-al organic hole-transport materials(HTMs),i.e.,PTAA[16]and spiro-OMeTAD[2,4,6].However,the highly efficient PSCs with the above organic hole-transport layers(HTL)usually suffer from instability.To facilitate hole transport and extraction,LiTF-SI and tBP are frequently employed to dope organic HTLs but this would sacrifice device stability.The use of these hygro-scopic p-dopants endows the devices with poor moisture sta-bility.

Perovskite solar cells with NiO_(x) hole-transport layer

Inverted perovskite solar cells(PSCs)have attracted interest due to their simple fabrication,long-term stability,and small hysteresis[1-3].It is noteworthy that the quality of the hole-transport layer(HTL)largely determines the device performance.Nickel oxide(NiO_(x))has been paid great attention as a hole-transport material in PSCs because of its natural p-type property,low cost,good stability,and high transmittance[4,5].

Ionic liquids in perovskite solar cells

Metal halide perovskites have gained a lot of attention particularly in recent years due to their excellent optoelectronic properties and simple scalable processability[1−3].One major application of halide perovskites is solar cells,however,despite the power conversion efficiencies(PCEs)have already reached around 25%[4,5],the long-term stability issue of such devices still impedes their commercialization.

2D perovskites for field-effect transistors

Metal halide perovskites have gained a lot of attention in the field of solar cells and light-emitting diodes because of their excellent optoelectronic properties and simple scalable processability[1-3].The exceptional structural tunability enables perovskites to possess low-dimensional form at the atomic level,offering advantages such as suppressed ion migrations and improved stability[4].Solar cells with power conversion efficiency over 19%have already been reported using quasi-two-dimensional(quasi-2D)Ruddlesden-Popper perovskites[5].Alternatively,2D perovskites could be used in field-effect transistors(FETs),which require horizontal charge transport,therefore avoiding the limitations of weak vertical charge transport in 2D perovskites while still maintaining the advantages such as suppressed ion migration and high intrinsic carrier mobility[6-8].