Metal halides perovskites, such as hybrid organic–inorganic CH3NH3PbI3, are newcomer optoelectronic materials that have attracted enormous attention as solution-deposited absorbing layers in solar cells with power conversion efficiencies reaching 20%. Herein we demonstrate a new avenue for halide perovskites by designing highly luminescent perovskite-based colloidal quantum dot materials. We have synthesized monodisperse colloidal nanocubes (4–15 nm edge lengths) of fully inorganic cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) using inexpensive commercial precursors. Through compositional modulations and quantum size-effects, the bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410–700 nm. The photoluminescence of CsPbX3 nanocrystals is characterized by narrow emission line-widths of 12–42 nm, wide color gamut covering up to 140% of the NTSC color standard, high quantum yields of up to 90%, and radiativ...

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Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut

Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

http://science.sciencemag.org/content/sci/345/6196/542.full.pdf

Interface engineering of highly efficient perovskite solar cells

The performance of solar cells based on organic–inorganic perovskites strongly depends on the device architecture and processing conditions. It is now shown that solvent engineering enables the deposition of very dense perovskite layers on mesoporous titania, leading to photovoltaic devices with a high light-conversion efficiency and no hysteresis.

Solvent engineering for high-performance inorganic–organic hybrid perovskite solar cells

Within the space of a few years, hybrid organic–inorganic perovskite solar cells have emerged as one of the most exciting material platforms in the photovoltaic sector. This review describes the rapid progress that has been made in this area.

The emergence of perovskite solar cells

The band gap of formamidinium lead iodide (FAPbI3) perovskites allows broader absorption of the solar spectrum relative to conventional methylammonium lead iodide (MAPbI3). Because the optoelectronic properties of perovskite films are closely related to film quality, deposition of dense and uniform films is crucial for fabricating high-performance perovskite solar cells (PSCs). We report an approach for depositing high-quality FAPbI3 films, involving FAPbI3 crystallization by the direct intramolecular exchange of dimethylsulfoxide (DMSO) molecules intercalated in PbI2 with formamidinium iodide. This process produces FAPbI3 films with (111)-preferred crystallographic orientation, large-grained dense microstructures, and flat surfaces without residual PbI2. Using films prepared by this technique, we fabricated FAPbI3-based PSCs with maximum power conversion efficiency greater than 20%.

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High-performance photovoltaic perovskite layers fabricated through intramolecular exchange

Improved understanding of the origins of instability during photovoltaic operation of perovskite solar cell materials must be established to overcome barriers to commercialization. In this study, we analyze the microscopic mechanisms of degradation in high-performing methylammonium free (FA 0.9 Cs 0.1 PbI 3 ) perovskite solar cells (PSC) over 600 hours of operation under stressors inherent to PV operation, including heat, illumination, and a load while excluding atmospheric effects by testing in a water-and oxygen-free atmosphere. While the PSCs exhibit reasonable thermal stability, they show considerable performance loss under constant illumination or stable power output. Synchrotron-based nanoprobe X-ray fluorescence and X-ray beam induced current (XRF/XBIC) measurements reveal segregation of current-blocking Cs-rich phases during stress testing. The decrease in performance correlates with the resulting number density of the Cs-rich clusters, which varies by stress condition. These findings unveil cation-dependent instability in FA0.9Cs0.1PbI3 perovskites and provide a framework for understanding the energy landscape in alloy perovskites to guide the engineering of long-lived halide perovskite devices.

The Impacts and Origins of A-site Instability in Formamidinium-Cesium Lead Iodide Perovskite Solar Cells Under Extended Operation

The long‐term stability issue of halide perovskite solar cells hinders their commercialization. The residual stress–strain affects device stability, which is derived from the mismatched thermophysical and mechanical properties between adjacent layers. In this work, we introduced the Rb2CO3 layer at the interface of SnO2/perovskite with the hierarchy morphology of snowflake‐like microislands and dendritic nanostructures. With a suitable thermal expansion coefficient, the Rb2CO3 layer benefits the interfacial stress relaxation and results in a compressive stress–strain in the perovskite layer. Moreover, reduced nonradiative recombination losses and optimized band alignment were achieved. An enhancement of open‐circuit voltage from 1.087 to 1.153 V in the resultant device was witnessed, which led to power conversion efficiency (PCE) of 22.7% (active area of 0.08313 cm2) and 20.6% (1 cm2). Moreover, these devices retained 95% of its initial PCE under the maximum power point tracking (MPPT) after 2700 h. It suggests inorganic materials with high thermal expansion coefficients and specific nanostructures are promising candidates to optimize interfacial mechanics, which improves the operational stability of perovskite cells.

Huanping Zhou

Papers

The Impacts and Origins of A-site Instability in Formamidinium-Cesium Lead Iodide Perovskite Solar Cells Under Extended Operation

Stress compensation based on interfacial nanostructures for stable perovskite solar cells