Mixed Organic-inorganic Halide Perovskite Research Articles

Phase segregation affects electron–phonon coupling in perovskite solar cell materials

Phase segregation has been described as a significant factor that limits solar cell efficiency and long-term stability in mixed organic–inorganic halide perovskite materials.

Improving Opto-Electronic Performance of Mixed-Cation Perovskite Solar Cells Through Surface-Treatment Strategy

Among thin-film solar cells, perovskite solar cells are receiving close review by the researchers due to rapid increase in efficiency during the last decade. Mixed organic–inorganic halide perovskites (CH3NH3PbI3 or MAPbI3) are easy in fabrication as well as cost-effective but these solar cells are facing challenges of stability under normal environmental conditions. Halide perovskite solar cells (PSCs) are polycrystalline in nature but still lacking the effective optical and electrical properties, and one of the big reasons behind it is the less grain size. In this study, formamidinium lead iodide (FAI) treatment was applied along with deposition of MAPbI3. The grain size was increased which further decreased defects of film surface and grain boundary between the grains. The treatment also helped improving the crystallinity of films, as well as opto-electronic characteristics of PSCs. The FAI treated PSCs showed more resilience stability than untreated PSCs in terms of aged power conversion efficiency (PCE). The complete investigation was done by comparing the scanning electron microscope (SEM) images, atomic force microscopy (AFM) images, X-ray diffraction peaks, UV-Vis absorbance and mean grain size of the FAI treated and non-FAI treated films.

A Study on the Effect of Ambient Air Plasma Treatment on the Properties of Methylammonium Lead Halide Perovskite Films

Organic-inorganic halide perovskite materials are considered excellent active layers in the fabrication of highly efficient and low-cost photovoltaic devices. This contribution demonstrates that rapid and low-temperature air-plasma treatment of mixed organic-inorganic halide perovskite film is a promising technique, controlling its opto-electrical surface properties by changing the ratio of organic-to-inorganic components. Plasma treatment of perovskite films was performed with high power-density (25 kW/m2 and 100 W/cm3) diffuse coplanar surface barrier discharge (DCSBD) at 70 °C in ambient air. The results show that short plasma treatment time (1 s, 2 s, and 5 s) led to a relatively enlargement of grain size, however, longer plasma treatment time (10 s and 20 s) led to an etching of the surface. The band-gap energy of the perovskite films was related to the duration of plasma treatment; short periods (≤5 s) led to a widening of the band gap from ~1.66 to 1.73 eV, while longer exposure (>5 s) led to a narrowing of the band gap to approx. 1.63 eV and fast degradation of the film due to etching. Surface analysis demonstrated that the film became homogeneous, with highly oriented crystals, after short plasma treatment; however, prolonging the plasma treatment led to morphological disorders and partial etching of the surface. The plasma treatment approach presented herein addresses important challenges in current perovskite solar cells: tuning the optoelectronic properties and manufacturing homogeneous perovskite films.

Influence of a Hole-Transport Layer on Light-Induced Degradation of Mixed Organic–Inorganic Halide Perovskite Solar Cells

Organic–inorganic halide perovskites (OIHPs) have been intensively studied in recent years for use in solar cells. Many studies have reported the light-induced phenomena of OIHP materials and their solar cells. In this study, we investigated the influence of a hole-transport layer (HTL) on light-induced degradation (LID) of mixed OIHP solar cells, especially at the OIHP/HTL interface, by hard X-ray photoelectron spectroscopy (HAXPES) and impedance spectroscopy. HAXPES shows accumulation of iodine and metallic lead in the vicinity of the OIHP/HTL and electron-transport layer/OIHP interfaces, respectively, after LID. Under light illumination and in the dark after LID, characteristic impedance responses are observed for a sample with a highly damaged OIHP/HTL interface as an intermediate frequency arc and negative capacitance, respectively, because of the electrochemical reaction in the vicinity of the OIHP/HTL interface. Overall, the results indicate that light-induced iodide diffusion to the OIHP/HTL inter...

Effect of organic cation states on electronic properties of mixed organic-inorganic halide perovskite clusters.

We study the effect of organic cation-centered states in mixed organic-inorganic halide perovskites on the bandstructure and optical properties. Clusters of methylammonium lead iodide (MAPbI3) and bromide (MAPbBr3) and of MAPbI3 (MAPbBr3) in which an organic cation was substituted with formamidinium (FA) and guanidinium (GA) are studied with density functional theory and time-dependent density functional theory. This model permitted comparing bandstructure and optical properties with different organic cations computed with GGA and hybrid functionals. We find that while with MA and GA, cation-centered states are deep in the conduction band, with FA, organic cation-centered states are introduced within as little as 0.5 eV of the conduction band maximum, which are expected to influence electronic and optical properties of perovskites in solar cells and other optoelectronic devices. There is qualitative agreement between a GGA and a hybrid functional; however, the use of a hybrid functional leads to a slightly higher offset of the cation-centered states from the conduction band edge, a different order of electronic states, and much better localization of cation-centered states. Analysis of optical absorption spectra suggests that occupation by photoexcitation of FA-centered states and formation of transient formamidinium species is possible in both I and Br-based perovskites.

Comparative Performance Study of Perovskite Solar Cell for Different Electron Transport Materials

In recent times, planar organo-metal halide perovskite solar cells (PSCs) achieved high power conversion efficiency (PCE > 22%). Mixed organic-inorganic halide perovskites, with excellent light harvesting properties, have evolved as a promising class of semiconductors for photovoltaics. In this work, compositional and electrical characterizations of materials used for different layers of PSC have been studied. One dimensional solar cell simulator wx-AMPS is used for numerical simulation of such devices and all simulations are done under AM1.5 illuminations and 300K temperature. Investigating the influences of thickness of electron transport material (ETM), hole transporting material (HTM) and absorber on the photovoltaic performance of PSCs, it is observed that, increase in thickness of perovskite (MAPbI3) results in the increase in PCE of solar cells, whereas increase in thickness of ETM layer results in decrease in the efficiency of the devices. The ETM plays a vital role on the performance of PSC. In this paper, for the first time performances of PSC for three different ETMs (TiO2, ZnO or SnO2) are calculated and analyzed simultaneously with the simulator wx-AMPS. The photovoltaic performances have been explored and efficiencies of 27.6%, 27.5% and 28.02% are reported for perovskite solar cells with TiO2, ZnO and SnO2 as ETM respectively for a specific thickness. Finally, this simulation study concludes that ZnO and SnO2 may be effective alternatives of the commonly used material, TiO2 as they are economically more potential and give somewhat better photovoltaic performance.
 Dhaka Univ. J. Sci. 66(2): 109-114, 2018 (July)

Nucleation and Crystallization Control via Polyurethane to Enhance the Bendability of Perovskite Solar Cells with Excellent Device Performance

AbstractSolar cells based on mixed organic–inorganic halide perovskites are promising photovoltaic technologies with low‐cost and fantastic power conversion efficiency (PCE). Enhancing the nucleation and regulating the crystallization rate of perovskite films and improving the bendability of brittle hybrid grains are crucial to improving the photovoltaic performance of flexible perovskite solar cells (PVSCs). Here, a simple approach is first introduced for fabricating perovskite films with full coverage and larger crystalline size by incorporating the elastomer polyurethane (PU) into the perovskite precursor solution to both retard the crystallization rate and improve the bendability. Shiny, smooth perovskite films are obtained with compact, micrometer‐sized crystalline grains that exhibit excellent photoelectric performances. The PVSCs fabricated by incorporating PU into the perovskite precursor offer an impressive PCE of 18.7% with almost no photocurrent hysteresis and excellent stability in ambient air. More importantly, the elastomer PU additive crosslinks the grain boundaries between neighboring perovskite crystals to form a PU network that effectively improves the bendability of the perovskite films.

Continuous Dripping Method as a Deposition Route for High-performance Mesoporous Perovskite Solar Cells

The past five years have witnessed the uniquely rapid emergence of the mixed organic-inorganic halide perovskite solar cells. Here, a modified deposition process, continuous dripping method, is reported for fabricating high-performance and reproducible perovskite solar cells. The best power conversion efficiency (PCE) of 17.76% and an average PCE of 16.74% were obtained via this process. Moreover, the conventional solution two steps method was also carried out as a comparison to this process. This work provides a new simple solution approach to obtain high quality of perovskite thin films for high-performance and reproducible PSCs.

Effect on the morphology and optical properties of CH3NH3PbI3 with additive of NH4Cl

Rapid emergence of solar cells based on mixed organic-inorganic halide perovskite have led to high power conversion efficiencies of over 20% in recent years. Looking for a simple and convenient way to fine-control of the perovskite film morphology is becoming one of the main issues. In this work, we explore the effect of adding NH4Cl on crystallization process and optical properties of perovskite. With adding NH4Cl, the perovskite films prepared by one-step method present better morphology than films without adding NH4Cl, namely, smoother surface and better coverage which result in uniform and much more stable photoluminescence intensities as well as longer lifetime of photoexcitations. More importantly, the photovoltaic cells fabricated with the addition of the NH4Cl have far better performance than the cells without additives. Therefore, one-step fabrication method can also control the morphology of perovskite films finely for both optical application and solar cells with adding proper additive.

Crack-free CH3NH3PbI3 layer via continuous dripping method for high-performance mesoporous perovskite solar cells

The past five years have witnessed the uniquely rapid emergence of the mixed organic-inorganic halide perovskite solar cells. Here, a modified deposition process, continuous dripping method, is reported for fabricating high-performance and reproducible perovskite solar cells. We have systematically investigated the impact of different molar ratio of lead iodide (PbI2) to dimethylsulfoxide (DMSO) on the growth, morphology and crystallinity of CH3NH3PbI3 (MAPbI3) films obtained via this process. The high power conversion efficiency (PCE) perovskite solar cell originates in crack-free and highly crystallographic perovskite films prepared with optimized ratio of PbI2 to DMSO in first precursor solution. The best PCE of 17.76% and an average PCE of 16.37±0.51% were obtained via this process. Moreover, the conventional solution two steps method was also carried out as a comparison to this process. This work provides a new simple solution approach to obtain high quality of perovskite thin films for high-performance and reproducible PSCs.

Polymer-templated nucleation and crystal growth of perovskite films for solar cells with efficiency greater than 21%

The past several years have witnessed the rapid emergence of a class of solar cells based on mixed organic–inorganic halide perovskites. Today’s state-of-the-art perovskite solar cells (PSCs) employ various methods to enhance nucleation and improve the smoothness of the perovskite films formed via solution processing. However, the lack of precise control over the crystallization process creates a risk of forming unwanted defects, for example, pinholes and grain boundaries. Here, we introduce an approach to prepare perovskite films of high electronic quality by using poly(methyl methacrylate) (PMMA) as a template to control nucleation and crystal growth. We obtain shiny smooth perovskite films of excellent electronic quality, as manifested by a remarkably long photoluminescence lifetime. We realize stable PSCs with excellent reproducibility showing a power conversion efficiency (PCE) of up to 21.6% and a certified PCE of 21.02% under standard AM 1.5G reporting conditions. Controlling the crystallization process of perovskite films is crucial to obtaining high efficiency in perovskite solar cells. Bi et al. propose the use of poly(methyl methacrylate) as a template for the controlled nucleation and growth of perovskite crystals achieving efficiency of 21.6%.

Potentials and challenges towards application of perovskite solar cells

The key progress in the development of solar cells based on mixed organic-inorganic halide perovskite was reviewed. Perovskite solar cells (PSCs) have developed rapidly and achieved highest efficiency exceeding 20% in these years. The origin, working principle and fabrication technology of PSCs are stated, and several promising methods to realize the industrialization of the solar cell modules have been put forward. Meanwhile, two main problems existing in PSCs have been pointed out, hysteresis in the photocurrent density-voltage measurement and the instability of perovskite, which have impacted the application of PSCs seriously. Efforts and study in order to solve these problems are also listed. The fundamental mechanism still needs further investigation so as to improve the performance of PSCs and realize their large-scale application eventually.

Beyond Efficiency: the Challenge of Stability in Mesoscopic Perovskite Solar Cells

Over the past five years, the rapid emergence of a new class of solar cell based on mixed organic–inorganic halide perovskite semiconductors has captured the attention of scientists and researchers in the field of energy conversion. Benefiting from the optimization of perovskite film deposition approaches, the design of new material systems, and the diversity of device concepts, the efficiency of perovskite solar cells (PSCs) has increased from 2.19% in 2006 to a certified 20.1% in 2014, making this the fastest‐advancing solar cell technology to date. However, as a photovoltaic technology, which needs to meet the requirements of working under long‐term sunlight, PSCs suffer stability concerns for both materials and devices. Evolved from dye‐sensitized solar cells (DSSCs), PSCs usually contain a mesoporous electron transporting layer or scaffold layer, a perovskite active layer, a hole transporting layer and a back contact to construct a mesoscopic‐structured device. Using interface engineering, mesoscopic PSCs (MPSCs) have obtained exciting stability with a hole‐conductor‐free printable triple‐layer architecture or conventional heterojunction version. Herein, the achievements of mesoscopic solar cells from solid‐state DSSCs to MPSCs are outlined and summary of recent progress in the stability of MPSCs is presented. Possible degradation mechanism and solutions are presented and, finally, challenges for the commercialization of this photovoltaic technology are discussed.

Room temperature optical properties of organic–inorganic lead halide perovskites

Past two years have seen the rapid emergence of a new class of solar cell based on mixed organic–inorganic halide perovskites. The optical and optical frequency dielectric properties of these perovskites at ambient temperatures are important both to the design of optimised solar cells and in other areas such as the refinement of electronic band structure calculations. Limited previous information has been published. The experimental optical and related dielectric constants of CH3NH3PbI3−xClx and CH3NH3PbI3 perovskite films are reported at 297K as determined by detailed analysis of reflectance and transmittance data. Absorption coefficients are also extracted from these data and compared with a range of previously reported values.

Benefit of Grain Boundaries in Organic-Inorganic Halide Planar Perovskite Solar Cells.

The past 2 years have seen the uniquely rapid emergence of a new class of solar cell based on mixed organic-inorganic halide perovskite. Grain boundaries are present in polycrystalline thin film solar cell, and they play an important role that could be benign or detrimental to solar-cell performance. Here we present efficient charge separation and collection at the grain boundaries measured by KPFM and c-AFM in CH3NH3PbI3 film in a CH3NH3PbI3/TiO2/FTO/glass heterojunction structure. We observe the presence of a potential barrier along the grain boundaries under dark conditions and higher photovoltage along the grain boundaries compare to grain interior under the illumination. Also, c-AFM measurement presents higher short-circuit current collection near grain boundaries, confirming the beneficial roles grain boundaries play in collecting carriers efficiently.

Correction to "Morphology and Carrier Extraction Study of Organic-Inorganic Metal Halide Perovskite by One- and Two-Photon Fluorescence Microscopy".

The past two years have seen the uniquely rapid emergence of a new class of solar-cell-based on mixed organic-inorganic halide perovskite. In this work, we demonstrate a promising technique for studying the morphology of perovskite and its impact on carrier extraction by carrier transport layer using one-photon and two-photon fluorescence imaging in conjunction with time-resolved photoluminescence. This technique is not only effective in separating surface and bulk effects but it also allows the determination of lifetimes in localized regions and local carrier extraction efficiency. The difference in sensitivities of transport materials to grain boundaries and film uniformity is highlighted in this study. It is shown that the PCBM fabricated in this work is more sensitive to film nonuniformity, whereas spiro-OMeTAD is more sensitive to grain boundaries in terms of effective carrier extraction.

Morphology and Carrier Extraction Study of Organic-Inorganic Metal Halide Perovskite by One- and Two-Photon Fluorescence Microscopy.

The past two years have seen the uniquely rapid emergence of a new class of solar-cell-based on mixed organic-inorganic halide perovskite. In this work, we demonstrate a promising technique for studying the morphology of perovskite and its impact on carrier extraction by carrier transport layer using one-photon and two-photon fluorescence imaging in conjunction with time-resolved photoluminescence. This technique is not only effective in separating surface and bulk effects but it also allows the determination of lifetimes in localized regions and local carrier extraction efficiency. The difference in sensitivities of transport materials to grain boundaries and film uniformity is highlighted in this study. It is shown that the PCBM fabricated in this work is more sensitive to film nonuniformity, whereas spiro-OMeTAD is more sensitive to grain boundaries in terms of effective carrier extraction.