Organic Hybrid Perovskite Research Articles

Measuring n and k at the Microscale in Single Crystals of CH3NH3PbBr3 Perovskite

Lead-based, inorganic–organic hybrid perovskites have shown much promise in photovoltaics, and the ability to tune their band gap makes them attractive for tandem solar cells, photodetectors, light-emitting diodes, and lasers. A crucial first step toward understanding a material’s behavior in such optoelectronic devices is determining its complex refractive index, n + ik; however, optically smooth films of hybrid perovskites are challenging to produce, and the optical properties of films of these materials have been shown to depend on the size of their crystallites. To address these challenges, this work reports quantitative reflectance and transmittance measurements performed on individual microcrystals of CH3NH3PbBr3, with thicknesses ranging from 155 to 1907 nm. The single crystals are formed by spin-coating a film of precursor solution and then stamping it with polydimethylsiloxane (PDMS) during crystallization. By measuring crystals of varying thickness, n and k values at each wavelength (405–1100 nm...

Optical Investigation of Broadband White-Light Emission in Self-Assembled Organic–Inorganic Perovskite (C6H11NH3)2PbBr4

The performance of hybrid organic perovskite (HOP) for solar energy conversion is driving a renewed interest in their light emitting properties. The recent observation of broad visible emission in layered HOP highlights their potential as white-light emitters. Improvement of the efficiency of the material requires a better understanding of its photophysical properties. We present in-depth experimental investigations of white-light (WL) emission in thin films of the (C6H11NH3)2PbBr4. The broadband, strongly Stokes shifted emission presents a maximum at 90 K when excited at 3.815 eV, and below this temperature coexists with an excitonic edge emission. X-rays and calorimetry measurements exclude the existence of a phase transition as an origin of the thermal behavior of the WL luminescence. The free excitonic emission quenches at low temperature, despite a binding energy estimated to 280 meV. Time-resolved photoluminescence spectroscopy reveals the multicomponent nature of the broad emission. We analyzed the...

High-performance flexible perovskite solar cells exploiting Zn2SnO4 prepared in solution below 100 °C.

Fabricating inorganic–organic hybrid perovskite solar cells (PSCs) on plastic substrates broadens their scope for implementation in real systems by imparting portability, conformability and allowing high-throughput production, which is necessary for lowering costs. Here we report a new route to prepare highly dispersed Zn2SnO4 (ZSO) nanoparticles at low-temperature (<100 °C) for the development of high-performance flexible PSCs. The introduction of the ZSO film significantly improves transmittance of flexible polyethylene naphthalate/indium-doped tin oxide (PEN/ITO)-coated substrate from ∼75 to ∼90% over the entire range of wavelengths. The best performing flexible PSC, based on the ZSO and CH3NH3PbI3 layer, exhibits steady-state power conversion efficiency (PCE) of 14.85% under AM 1.5G 100 mW·cm−2 illumination. This renders ZSO a promising candidate as electron-conducting electrode for the highly efficient flexible PSC applications.

Ferroelectric solar cells based on inorganic–organic hybrid perovskites

Ferroelectric solar cells were fabricated by using the inorganic–organic hybrid perovskite materials, and power conversion efficieny as high as 6.7% had been obtained based on the MAPbI3−xClxthin film. This work provides an alternative avenue for high-performance ferroelectric solar cells beyond inorganic ferroelectric oxides.

Solution Chemistry Engineering toward High-Efficiency Perovskite Solar Cells.

Organic and inorganic hybrid perovskites (e.g., CH3NH3PbI3) have emerged as a revolutionary class of light-absorbing semiconductors that has demonstrated a rapid increase in efficiency within a few years of active research. Controlling perovskite morphology and composition has been found critical to developing high-performance perovskite solar cells. The recent development of solution chemistry engineering has led to fabrication of greater than 15-17%-efficiency solar cells by multiple groups, with the highest certified 17.9% efficiency that has significantly surpassed the best-reported perovskite solar cell by vapor-phase growth. In this Perspective, we review recent progress on solution chemistry engineering processes and various control parameters that are critical to the success of solution growth of high-quality perovskite films. We discuss the importance of understanding the impact of solution-processing parameters and perovskite film architectures on the fundamental charge carrier dynamics in perovskite solar cells. The cost and stability issues of perovskite solar cells will also be discussed.

Recent Progress of Lead Halide Perovskite Sensitized Solar Cells

Low cost organic and inorganic hybrid perovskites such as CH3NH3PbI3 has demonstrated a rapid increase in efficiency and has attracted tremendous research effort within a few years. The perovskite solar cells has evolved from tradi- tional sensitized solar cell using liquid iodine electrolyte to solid state solar cell with either mesoporous or planar structure. The morphology controllable solution chemistry deposition of perovskite has progress into 15%~17% efficiency perovoskite solar cells reported by several groups. The perovskite sensitized solar cells has also progress from pure mesoporous structure into meso-planar hybrid one, which has the advantages of high efficiency and better stability. Here we review recent progress on the development of perovskite sensitized solar cells, different band gap perovskites and their deposition, different back- bone nanostructures and their charge transfer properties. Keywords lead halide perovskite; solar cell; sensitized; mesoporous

Polyfluorene Derivatives are High‐Performance Organic Hole‐Transporting Materials for Inorganic−Organic Hybrid Perovskite Solar Cells

Photovoltaics based on organic−inorganic perovskites offer new promise to address the contemporary energy and environmental issues. These solar cells have so far largely relied on small‐molecule hole transport materials such as spiro‐OMeTAD, which commonly suffer from high cost and low mobility. In principle, polyfluorene copolymers can be an ideal alternative to spiro‐OMeTAD, given their low price, high hole mobility and good processability, but this potential has not been explored. Herein, polyfluorene derived polymers‐TFB and PFB, which contain fluorine and arylamine groups, are demonstrated and can indeed rival or even outperform spiro‐OMeTAD as efficient hole‐conducting materials for perovskite solar cells. In particular, under the one‐step perovskite deposition condition, TFB achieves a 10.92% power conversion efficiency that is considerably higher than that with spiro‐OMeTAD (9.78%), while using the two‐step perovskite deposition method, about 13% efficient solar cells with TFB (12.80%) and spiro‐OMeTAD (13.58%) are delivered. Photo­luminescence reveals the efficient hole extraction and diffusion at the interface between CH3NH3PbI3 and the hole conducting polymer. Impedance spectroscopy uncovers the higher electrical conductivity and lower series resistance than spiro‐OMeTAD, accounting for the significantly higher fill factor, photocurrent and open‐circuit voltage of the TFB‐derived cells than with spiro‐MeOTAD.

Understanding quantum confinement of charge carriers in layered 2D hybrid perovskites.

Layered hybrid organic perovskites (HOPs) structures are a class of low-cost two-dimensional materials that exhibit outstanding optical properties, related to dielectric and quantum confinement effects. Whereas modeling and understanding of quantum confinement are well developed for conventional semiconductors, such knowledge is still lacking for 2D HOPs. In this work, concepts of effective mass and quantum well are carefully investigated and their applicability to 2D HOPs is discussed. For ultrathin layers, the effective-mass model fails. Absence of superlattice coupling and importance of non-parabolicity effects prevents the use of simple empirical models based on effective masses and envelope function approximations. An alternative method is suggested in which 2D HOPs are treated as composite materials, and a first-principles approach to the calculation of band offsets is introduced. These findings might also be relevant for other classes of layered 2D functional materials.

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

Organolead trihalide perovskite materials have been successfully used as light absorbers in efficient photovoltaic cells. Two different cell structures, based on mesoscopic metal oxides and planar heterojunctions have already demonstrated very impressive advances in performance. Here, we report a bilayer architecture comprising the key features of mesoscopic and planar structures obtained by a fully solution-based process. We used CH3NH3 Pb(I(1-x)Br(x))3 (x = 0.1-0.15) as the absorbing layer and poly(triarylamine) as a hole-transporting material. The use of a mixed solvent of γ-butyrolactone and dimethylsulphoxide (DMSO) followed by toluene drop-casting leads to extremely uniform and dense perovskite layers via a CH3NH3I-PbI2-DMSO intermediate phase, and enables the fabrication of remarkably improved solar cells with a certified power-conversion efficiency of 16.2% and no hysteresis. These results provide important progress towards the understanding of the role of solution-processing in the realization of low-cost and highly efficient perovskite solar cells.

Well-Organized Mesoporous TiO2 Photoelectrodes by Block Copolymer-Induced Sol–Gel Assembly for Inorganic–Organic Hybrid Perovskite Solar Cells

A well-aligned mesoporous thin layer was formed by spin-coating followed by the burn-out of its organic components at 500 °C. This film, prepared by an inorganic sol–gel process using block copolymers as a sacrificial template, showed mesoporous (mp) and crack-free layers with various pore sizes depending on the amount of 1,3,5-trimethylbenzene (TMB), which acted as a swelling agent. The mesoporous photoanodes were used in the fabrication of CH3NH3Pb(I0.9Br0.1)3 perovskite-based solar cells. The cells showed overall power conversion efficiencies of 11.7% and 12.8% with the 10 and 15 nm mp-layers, respectively. The superior performance shown in the 15 nm mp-layers may be attributed to the easier filling of CH3NH3Pb(I0.9Br0.1)3 by bigger pore sizes, and the efficiency is comparable with that of the reference cell fabricated by TiO2 paste. This template-induced self-organizing sol–gel process was shown to be a useful technique for depositing mesoporous photoanodes in the fabrication of perovskite-based solar...

Back Cover: DFT and k · p modelling of the phase transitions of lead and tin halide perovskites for photovoltaic cells (Phys. Status Solidi RRL 1/2014)

Perovskites for photovoltaics: Three-dimensional hybrid organic perovskites, CH3NH3PbX3 (X = I, Br, Cl), have recently been used to strongly improve the efficiency of dye sensitized solar cells (DSSC) leading to a new class of low-cost mesoscopic solar cells. Density functional theory (DFT) and many body (GW) corrections are used by Jacky Even et al. (pp. 31–35) to compare lead and tin hybrid and all-inorganic perovskites. The room-temperature optical absorption is associated to electronic transitions between the spin–orbit split-off band in the conduction band and the valence band. The low-temperature excitonic effect is studied by comparing the RPA and the Bethe–Salpeter (BSE) computation of the dielectric constant. Spin–orbit coupling is about three times smaller for tin. The recently reported phases of CH3NH3MI3 (where M = Pb, Sn) close to the room-temperature and tetragonal distortions from the ideal cubic phase, are analysed by a k·p perturbation, including spin–orbit effect. In addition, the non-centrosymmetric phases of CH3NH3MI3 exhibit a splitting of the electronic bands away from the critical point.

Efficient Inorganic–Organic Hybrid Perovskite Solar Cells Based on Pyrene Arylamine Derivatives as Hole-Transporting Materials

A set of three N,N-di-p-methoxyphenylamine-substituted pyrene derivatives have successfully been synthesized and characterized by (1)H/(13)C NMR spectroscopy, mass spectrometry, and elemental analysis. The optical and electronic structures of the pyrene derivatives were adjusted by controlling the ratio of N,N-di-p-methoxyphenylamine to pyrene, and investigated by UV/vis spectroscopy and cyclic voltammetry. The pyrene derivatives were employed as hole-transporting materials (HTMs) in fabricating mesoporous TiO2/CH3NH3PbI3/HTMs/Au solar cells. The pyrene-based derivative Py-C exhibited a short-circuit current density of 20.2 mA/cm(2), an open-circuit voltage (Voc) of 0.886 V, and a fill factor of 69.4% under an illumination of 1 sun (100 mW/cm(2)), resulting in an overall power conversion efficiency of 12.4%. The performance is comparable to that of the well-studied spiro-OMeTAD, even though the Voc is slightly lower. Thus, this newly synthesized pyrene derivative holds promise as a HTM for highly efficient perovskite-based solar cells.

DFT and k · p modelling of the phase transitions of lead and tin halide perovskites for photovoltaic cells

Abstract3D hybrid organic perovskites, CH3NH3PbX3 (X = halogen), have recently been used to strongly improve the efficiency of dye sensitized solar cells (DSSC) leading to a new class of low‐cost mesoscopic solar cells. CsSnI3 perovskite can also be used for hole conduction in DSSC. Density functional theory and GW corrections are used to compare lead and tin hybrid and all‐inorganic perovskites. The room temperature optical absorption is associated to electronic transitions between the spin–orbit split‐off band in the conduction band and the valence band. Spin–orbit coupling is about three times smaller for tin. Moreover, the effective mass of relevant band edge hole states is small (0.17). The high temperature phase sequence of CsSnI3 leading to the room temperature orthorhombic phase and the recently reported phases of CH3NH3MI3 (where M = Pb, Sn) close to the room temperature, are also studied. Tetragonal distortions from the ideal cubic phase are analysed by a k · p perturbation, including spin–orbit effect. In addition, the non‐centrosymmetric phases of CH3NH3MI3 exhibit a splitting of the electronic bands away from the critical point. The present work shows that their physical properties are more similar to conventional semiconductors than to the absorbers used in DSSC. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The structure and photoluminescence of chiral tin and lead inorganic–organic hybrid perovskites

The structure and photoluminescence of chiral tin and lead inorganic–organic hybrid perovskites

Poly[bis[2-(1-cyclohexenyl)ethylammonium] di-μ-iodo-diodoplumbate(II)

The title compound, (C(8)H(16)N)(2)[PbI(4)], crystallizes as an inorganic-organic hybrid perovskite, adopting the unusual 2a(p) x 2a(p) superstructure. As such, the structure consists of two-dimensional sheets of corner-sharing PbI(6) octahedra in the ab plane, separated by bilayers of 2-(1-cyclohexenyl)ethylammonium cations. The ethylammonium groups are not in the plane of the cyclohexenyl rings.