Iodine Chemistry Dictating Stability of Metal Halide Perovskites

The thermodynamic and redox properties of halide perovskites provide a strong driving force for hole trapping and oxidation of iodide species. When in contact with a non-polar solvent, the migration of iodine species is further extended to expulsion of iodine from the perovskite film. Thus, the mobility of halides and their susceptibility to hole-induced oxidation play a crucial role in determining the long-term stability of metal halide perovskite solar cells. When Ruddlesden-Popper 2D mixed-halide perovskite films with spacer cations such as butylammonium are introduced into three-dimensional (3D) perovskite films, they can stabilize them against moisture-induced degradation at room temperature. While such passivation of 3D perovskites using 2D perovskites has been reported widely, the instability of the 2D/3D interface during long term solar cell operation can be problematic, especially at higher temperatures. The cation migration under light and heat can significantly alter the 2D/3D interface, thus affecting the solar cell performance. We have now probed the cation migration between 2D and 3D perovskites by physically pairing X PbI (X=butylammonium BA, oleylammonium OA, or phenethylammonium PEA) 2D film and (CH3)PbI3 3D film at different temperatures by recording changes in the absorption and emission spectra. Thus, suppression of halide ion migration as well as cation migration remains a key factor in achieving long term stability and improving efficiency of perovskite solar cells and light emitting devices.

Influence of Charge Transport Layers on Capacitance Measured in Halide Perovskite Solar Cells

Heteroleptic Tin-Antimony Sulfoiodide for Stable and Lead-free Solar Cells

Lead-free tin perovskite solar cells

The ability to tune the bandgap of metal halide perovskites through compositional alloying of the halide ion is of interest in designing tandem solar cells and light emitting displays. However, photoinduced migration of halide ions can significantly affect the device performance. One such property is photoinduced phase segregation in mixed halide perovskites (MHP), which forms bromide rich and iodide-rich domains. These domains act as charge carrier traps and lower the efficiency of perovskite-based devices.[1,2] The thermodynamic and redox properties of halide perovskites provide a strong driving force for hole trapping and oxidation of iodide species. Thus, the mobility of halides and their susceptibility to hole-induced oxidation play a crucial role in determining the long-term stability of metal halide perovskite solar cells.When Ruddlesden-Popper 2D mixed-halide perovskite films with spacer cations such as butylammonium are introduced into three-dimensional (3D) perovskite films, they can stabilize them against moisture-induced degradation at room temperature. While such passivation of 3D perovskites using 2D perovskites has been reported widely, the instability of the 2D/3D interface during long term solar cell operation can be problematic.[3,4] The cation migration under light and heat can significantly alter the 2D/3D interface, thus affecting the solar cell performance. Thus, suppression of halide ion migration as well as cation migration remains a key factor in achieving long term stability and improving efficiency of perovskite solar cells and light emitting devices.

High-performance methylammonium-free ideal-band-gap perovskite solar cells

Decoupling the effects of defects on efficiency and stability through phosphonates in stable halide perovskite solar cells

Crossing Up Charge Extraction Layers

Shallow Iodine Defects Accelerate the Degradation of α-Phase Formamidinium Perovskite

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Halide Perovskites for Selective Ultraviolet-Harvesting Transparent Photovoltaics

Organic–inorganic metal halide perovskite solar cells (PSCs) are one of the emerging technologies in photovoltaic research. The certified maximum power conversion efficiency (PCE) of PSCs has reached as high as 25%. In particular, the development of hole transport layer (HTL) materials plays a key role in increasing PCEs. Among a vast number of HTL materials developed to date, the most common HTL material is 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD), because it can provide very high performance in PSCs. Besides the high PCE, the issue of long-term stability is of paramount importance. The room-temperature operational stability of PSCs with the spiro-OMeTAD HTL has been improved significantly past few years, but it is still low, compared with Si-based technology. In addition, the instability at high temperature is the Achilles heel of PSCs with the spiro-OMeTAD HTL. Although the low operational stability of PSCs, especially at high temperature, is generally associated with instability of spiro-OMeTAD, the high-temperature stability has been improved significantly by understanding the degradation mechanisms. In this mini-review, we discuss the degradation mechanisms and suggest our perspectives to overcome the degradation. Thus, this mini-review will guide the development of stable PSCs with the spiro-OMeTAD HTL and the design of new HTL materials to replace spiro-OMeTAD toward commercialization of PSCs in the future.

Single-crystal halide perovskites: Opportunities and challenges

Metal halide perovskite solar cells have now reached efficiencies of over 22%. To date, the most efficient perovskite solar cells have the n-i-p device architecture and use 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene or poly(triarylamine) as the hole transport material (HTM), which are typically doped with lithium bis((trifluomethyl)sulfonyl)amide (Li-TFSI). Li-TFSI is hygroscopic and detrimental to the long-term performance of the solar cells, limiting its practical use. In this work, we successfully replace Li-TFSI by molybdenum tris(1-(methoxycarbonyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), Mo(tfd-CO2Me)3, or molybdenum tris(1-(trifluoroacetyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), Mo(tfd-COCF3)3. With these two dopants, we achieve stabilized power conversion efficiencies up to 16.7% and 15.7% with average efficiencies of 14.8% ± 1.1% and 14.4% ± 1.2%, respectively. Moreover, we observe a significant enhancement of the long-term stability of perovskite solar cells und...

Photovoltaics literature survey (no. 149)