Morphology Of Perovskite Films Research Articles

Highly efficient, low-cost, lead-free bifacial perovskite solar cells: A designing strategy through simulation

The bipolar properties of perovskites make it fascinating to design a perovskite solar cell (PSC) without a hole transport layer (HTL). An HTL-free PSCs provide easy fabrication, are low-cost, and time-saving. In HTL-free PSCs, the crystallinity and morphology of perovskite film can enhance device performance. With the bifacial approach, the device efficiency can be further enhanced. In the present work, HTL-free bifacial PSCs have been simulated, and a strategy has been provided to design a high-performance device. In investigating the effect of various electron transport layers (ETLs) and lead-free perovskite layers, we observed that a suitable combination of ETL and perovskite is vital to achieve a higher power conversion efficiency (PCE). The Mott-Schottky analysis of ETL/perovskite interfaces reveals that the built-in potential depends on the bandgap of the perovskite absorber layer, which affects the device performance by setting up higher open circuit voltage (VOC). A higher dielectric material between the ETL and the perovskite layer improves the device performance. Additionally, lowering the doping density of the perovskite layer increases the bifacial factor of the device. While optimizing our cells, the champion device with configuration FTO/Zn2SnO4/MASnI3/UT-Au (ultra-thin gold) exhibits a PCE of 19.76 % and 15.97 % for the front and rear illumination, respectively. By replacing UT-Au with MAM(MoOx/Ag/MoOx) transparent conducting triple-layer electrode, our device shows an improved PCE of >25 % for both front and rear illumination. The outcomes of these studies are anticipated to be beneficial in designing and optimizing HTL-free bifacial PSCs in the experiment.

Constructing low-dimensional perovskite network to assist efficient and stable perovskite solar cells

The use of low-dimensional (LD) perovskite materials is crucial for achieving high-performance perovskite solar cells (PSCs). However, LD perovskite films fabricated by conventional approaches give rise to full coverage of the underlying 3D perovskite films, which inevitably hinders the transport of charge carriers at the interface of PSCs. Here, we designed and fabricated LD perovskite structure that forms net-like morphology on top of the underlying 3D perovskite bulk film. The net-like LD perovskite not only reduced the surface defects of 3D perovskite film, but also provided channels for the vertical transport of charge carriers, effectively enhancing the interfacial charge transfer at the LD/3D hetero-interface. The net-like morphological design comprising LD perovskite effectively resolves the contradiction between interfacial defect passivation and carrier extraction across the hetero-interfaces. Furthermore, the net-like LD perovskite morphology can enhance the stability of the underlying 3D perovskite film, which is attributed to the hydrophobic nature of LD perovskite. As a result, the net-like LD perovskite film morphology assists PSCs in achieving an excellent power conversion efficiency of up to 24.6% with over 1000 h long-term operational stability.

Retrograde Solubility of Methylammonium Lead Iodide in γ-Butyrolactone Does Not Enhance the Uniformity of Continuously Coated Films.

Halide perovskite thin films can be the centerpiece of high-performance solar cells, light-emitting diodes, and other optoelectronic devices if the films are of high uniformity and relatively free of pinholes and other defects. A common strategy to form dense films from solution has been to generate a high density of nuclei by rapidly increasing supersaturation, for example, by timely application of an antisolvent or forced convection. In this work, we examine the role of retrograde solubility, wherein solubility decreases with increasing temperature, as a means of increasing the nucleation density and film coverage of slot-die-coated methylammonium lead iodide (MAPbI3) from γ-butyrolactone (GBL) solution. Coverage was investigated as a function of the substrate temperature and the presence and temperature of an air knife. Results were considered within the framework of the dimensionless modified Biot number, which quantifies the interplay between evaporation and horizontal diffusion. Moderate temperatures and a heated air knife improved film coverage and morphology by enhanced nucleation up to ∼80 °C. However, despite the dense nucleation enabled by retrograde solubility, slow evaporation as a result of the low vapor pressure of GBL, combined with Ostwald ripening at high temperatures, prevented the deposition of void-free, device-quality films. This work has provided a more detailed understanding of the interplay between perovskite processing, solvent parameters, and film morphology and ultimately indicates the obstacles to forming dense, uniform films from solvents with high boiling points even in the presence of rapid nucleation.

Effect of Spin Coat Speed on Structure, Composition and Properties of Perovskite Films

Recently, 2D perovskite has emerged as a promising alternative material for solar cell applications because of its superior stability in wet environments. Among the various methods for preparing 2D perovskite films, spin coat is the most widely used due to its low pollution, high accuracy and energy efficiency. In this study, the effects of spin coat speed on the surface morphology, crystal structure and surface composition of 2D perovskite (BA2MA3Pb4I13) films are investigated using X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy and other techniques. It is found that the BA2MA3Pb4I13 film has large crystal size, good crystallinity and small lattice constant at a relatively low spin coat speeds. The device performance test showed that the BA2MA3Pb4I13 film can obtain better device performance as well. It indicated that the photovoltaic performance of perovskite solar cells can be significantly improved by optimization of the fabrication parameters during the film preparation process.

Enhancing Stability and Photovoltaic Performance of Perovskite Solar Cells via 5‐Ammonium Acid Additive

AbstractThe quality of perovskite films plays a fundamental role in determining the performance of perovskite solar cells (PSCs). It is widely recognized that achieving high crystalline quality and minimizing defect density in perovskite films are essential. In this study, the utilization of the multifunctional additive 5‐ammonium acid (5‐AVA) to improve the morphology of perovskite films is proposed. The ‐NH2 and ‐COOH groups in 5‐AVA enable effective coordination with Pb ions and organic ions in perovskite, resulting in the suppression of defect formation and the reduction of non‐radiative recombination losses. Furthermore, the addition of 5‐AVA facilitates a more favorable energy level alignment, thereby enhancing the transfer of carriers between the perovskite layer and transport layers. Consequently, this process contributes to the improvement of the open circuit voltage (VOC) in PSCs. Attributing to the addition of 5‐AVA, the optimized PSCs achieve significantly enhanced performance with a maximum photoelectric conversion efficiency (PCE) of 24.74% and excellent long‐term stability. This work presents a straightforward and effective approach to enhance the performance and long‐term stability of PSCs.

Dimethylamine oxalate manipulating CsPbI3 perovskite film crystallization process for high efficiency carbon electrode based perovskite solar cells

Crystallization process determines the quality of perovskite films and the performances of resultant perovskite solar cells (PSCs). Dimethylamine oxalate has been proven as a multifunctional modulator, and is explored as an efficient additive in manipulating the crystallization process of CsPbI3 perovskite films. On one hand, oxalate serves as the precipitator that facilitates the nucleation process of intermediate. The larger size of intermediate is conductive to the larger size and smaller grain boundaries of resultant perovskite. On the other hand, in subsequent annealing process, the phase conversion and growth process of transient perovskite can be decelerated due to the strong interactions of oxalate with both dimethylamine cation (DMA+) and Pb2+. Due to the optimized crystallization kinetics, the morphology and quality of CsPbI3 perovskite films are comprehensively improved with lower defect concentrations, and charge recombination loss is effectively suppressed. Benefiting from the optimized crystal quality of perovskite films, the carbon electrode-based CsPbI3 PSCs exhibit a champion efficiency of 18.48%. This represents one of the highest levels among all hole transport layer-free inorganic perovskite solar cells.

Improvement of performance of perovskite solar cells through BaTiO<sub>3</sub> doping regulated built-in electric field

The preparation of hybrid perovskite solar cells is expensive and environmentally demanding. Carbon-based HTL-free perovskite solar cells (C-PSCs) have attracted much attention because they replace the expensive precious metal electrode and remove the poor stability of the hole transport material. However, the improvement of efficiency is hampered by poor carrier separation and transport performance within C-PSCs, while the enhancement of the built-in electric field can improve the carrier transport performance, thus enhancing photoelectric performance. The built-in electric field can be regulated by doping. The anomalous photovoltaic effect and the built-in electric field of ferroelectric material play an important role in the field of optoelectronics. In this work, a simple and effective method is developed to improve the performance of perovskite solar cells via the combination of internal doping of ferroelectric polymer and external control of electric field. Ferroelectric material barium titanate (BaTiO<sub>3</sub>) powder is added into perovskite precursor solution as an additive to prepare C-PSCs, which can improve the perovskite film morphology, reduce the film defect density, and enhance the carrier transport performance of C-PSCs. The results show that when the addition of BaTiO<sub>3</sub> is 1.0% (mass fraction), the perovskite film is uniform and dense, and the photoelectric conversion efficiency of the cell is the highest. After the forward voltage polarization treatment, the residual polarized electric field of ferroelectric material BaTiO<sub>3</sub> increases the built-in electric field, which provides sufficient power for realizing carrier transport and extraction, thus inhibiting the occurrence of non-radiative recombination. At the same time, the depletion layer width is increased, and the reverse saturation current is reduced, so the cell performance is significantly improved. The optimal device efficiency is 9.02%. This work provides an efficient strategy for regulating the built-in electric field by doping perovskite absorption layer.

Ruthenium Complex Optimized Contact Interfaces of NiOX Nanocrystals for Efficient and Stable Perovskite Solar Cells

Nickel oxide (NiO X ) is a desirable hole‐transporting material for perovskite solar cells owing to their merits of low‐cost, stable, and readily scalable. However, the NiO X |perovskite interface suffers from serious recombination and poor photostability because of the interfacial redox reactions. Herein, NiO X nanoparticles with tunable size have been synthesized at low temperatures by controlling the reactivity of the hydrolysis reaction. A self‐assembled monolayer composed of a ruthenium complex, i.e., C106, is then introduced to optimize the interfacial properties. The C106 molecule chemically bonds to NiO X via carboxyl acid group, which passivates the surface defects of NiO X and suppresses the negative redox reaction at the interface. The modification leads to an improvement in perovskite film morphology, crystallization, and band alignment. As a result, the efficiency of solar cells has been improved from 18.1% to 20.5%. More importantly, the modified solar cells retain >80% of their initial performance after continuous operation under 100 mW cm−2 irradiation for 800 h, which is much enhanced than the unmodified devices.

Grain Characteristics of Perovskite Thin Films Based on SEM Image Segmentation

AbstractPerovskite solar cells (PSCs) have become the forefront and hot pot of new photovoltaic technology due to their high efficiency, low cost, and easy preparation. Understanding the microstructure characteristics of the perovskite films is one of the key factors to further improve the efficiency and stability. The characteristics of grains based on the self‐developed perovskite film morphology analysis software GrainD are studied in this article. Important perovskite film information such as the average radius of grains, the distribution pattern of grain size, the area of grain contact, and the total number of grains are obtained. The results show that the grain size distribution of the polycrystalline perovskite film follows the lognormal distribution. According to statistical probability theory and grain growth theory, the multiplication effect of multiple random factors of film growth is proposed as the reason for the lognormal distribution. This study provides an important method for analyzing the perovskite films and gives clues about the crystallization kinetics.

Abnormal high stability halide perovskite thin films and solar cells to alpha and gamma irradiations with varying fluence

Solar cells (SCs) and thin films made of methylammonium lead tri-iodide (MAPbI3) have demonstrated remarkable robustness when irradiated with alpha (He2+) and gamma radiations from americium-241. This study investigates changes in the structure, absorption, and surface morphology of perovskite thin films, as well as the photoelectronic properties of MAPbI3 SCs, with and without irradiation with He2+. According to the XRD analysis, tetragonal MAPbI3 showed increased crystallinity and a decrease in compression micro-strain with an increased flux of He2+. UV–Vis absorption remained unchanged until the flux exceeded 7.36 x 1012 He2+ cm−2. The bandgaps for irradiated films decreased similarly to pristine films up to a dose of 3.07 x 1012 He2+cm−2, with significant differences observed beyond this point. Digital images showed significant changes in thin films irradiated at fluences exceeding 3.07 x 1012 He2+ cm−2, with pits forming in grains responsible for the changes, confirmed by scanning electron microscopy. In conclusion, this study found that MAPbI3 thin films and SCs can withstand doses of He2+ up to 3.07 x 1012 He2+ cm−2 in a He2+ radiation environment.

Ionic surfactants of different dipole moments as anti-solvent additives for air-processing MAPbI3−xClx perovskite thin films

Three ionic surfactants, didodecyldimethylammonium bromide (DDABr), sodium lauryl ether sulfate (NaLES) and sodium lauryl sulfate (NaLS), with different dipole moment values: 0.907, 17 and 212 Debye, respectively, have been used as anti-solvent additives to remove the moisture from perovskite precursor solutions. The three additives impact in different ways on the crystallinity, wettability and morphology of perovskite thin films, as well as on the stability and efficiency of air-processed perovskite solar cells (PSCs). The hydrophobic groups of the additives at the surface of perovskite thin films help to increase the stability of PSCs, especially DDABr of the lowest dipole moment. On the other hand, NaLES, of the highest dipole moment, is the most efficient to extract moisture from the perovskite precursor coatings, increasing the average power conversion efficiency (PCE) of NaLES-based PSCs from 16.16 ± 0.94% to 17.21 ± 0.32% in comparison with that of the reference. Furthermore, the synergy between NaLES and the perovskite precursor additive, KI, achieves the best photovoltaic performance of the PSCs, leading to an average PCE of 17.42% and the best PCE of 18.75%. It is concluded that ionic surfactants of different dipole moments are good candidates as anti-solvent additives to improve the efficiency and stability of air-processed PSCs.

A Practical Approach Toward Highly Reproducible and High-Quality Perovskite Films Based on an Aging Treatment.

Solution processing of hybrid perovskite semiconductors is a highly promising approach for the fabrication of cost-effective electronic and optoelectronic devices. However, challenges with this approach lie in overcoming the controllability of the perovskite film morphology and the reproducibility of device efficiencies. Here, a facile and practical aging treatment (AT) strategy is reported to modulate the perovskite crystal growth to produce sufficiently high-quality perovskite thin films with improved homogeneity and full-coverage morphology. The resulting AT-films exhibit fewer defects, faster charge carrier transfer/extraction, and suppressed non-radiative recombination compared with reference. The AT-devices achieve a noticeable improvement in the reproducibility, operational stability, and photovoltaic performance of devices, with the average efficiency increased by 16%. It also demonstrates the feasibility and scalability of AT strategy in optimizing the film morphology and device performance for other perovskite components including MAPbI3 , (MAPbBr3 )15 (FAPbI3 )85 , and Cs0.05 (MAPbBr3 )0.17 (FAPbI3 )0.83 . This method opens an effective avenue to improve the quality of perovskite films and photovoltaic devices in a scalable and reproducible manner.

Minimized defective trap sites in perovskite absorber films by coumarin dye for efficient and reliable perovskite solar cells

This study presents a defect passivation approach using coumarin dye (7-diethylaminobenzopyran-2-one) as a multi-functional passivating agent of perovskite films to boost power conversion efficiency (PCE) and operating stability of PSCs. The coumarin dye could offer strong interaction with under-coordinated Pb2+ and vacant I− in [PbI6] octahedral frameworks due to multiple functional groups, which could serve as potential Lewis bases or hydrogen bonding sites, as well as highly conjugated aromaticity. The incorporation of coumarin dye contributes to improved film morphology of perovskite films, leading to compact and uniform grains without compromising crystallinity. Correspondingly, enhanced carrier extraction/transport and suppressed trap-assisted recombination are promoted in the perovskite films modified with coumarin dye. As a result, the coumarin dye incorporation improved the photovoltaic performance delivering a PCE of 20.85 % in planar p-i-n PSCs. The optimized device also recorded excellent indoor photovoltaic performance (PCE = 30.35 %) under dim-light condition. Furthermore, the devices passivated with coumarin dye also maintained >90 % of their initial PCEs after exposed under continuous indoor lighting irradiation (1000 lux) in ambient atmosphere for 2000 h, exhibiting impressive reliability and practical applicability.

Ionic liquid optimized buried interface between spray-coated NiOX and perovskite for efficient solar cells

Spray-coated nickel oxide (NiOX) has great potential as hole transport layer for the fabrication of efficient, stable metal halide perovskite solar cells (PSCs). However, emerging evidences demonstrate that the inferior contact and the redox reaction at the NiOX|perovskite buried interface limit the performance of the devices. Herein, a series of ionic liquids were selected to modulate this interface as well as the perovskite film morphology. The results show that 1-butyl-3-methylimidazole tetrafluoroborate (BMIMBF4) exhibits a strong interfacial coupling effect between NiOX and perovskite, which facilitates the perovskite crystallization and charge transfer at the interface. As a result, the BMIMBF4 enables an efficiency improvement from 17.7% to 20.1% (aperture area: 0.16 cm2). More importantly, the non-encapsulated devices retain 90% of their initial performance after aging under ambient conditions for 700 h (ISOS-D-1).

Advancing perovskite solar cell performance: Enhanced efficiency and stability through superimposed PbS QDs

This study investigates enhancing efficiency in thin-film photovoltaic devices by incorporating varying-sized superimposed PbS colloidal quantum dots (CQDs). These CQDs offer tunable near-infrared absorption, multiple exciton generation effects, and solution processability, rendering them promising for improved performance. Superimposing QDs of different sizes extends the device's absorption spectrum beyond conventional limits, utilizing tailored absorption coefficients for broader sunlight wavelength utilization and increased solar energy conversion efficiency. Each QD group exhibits a unique absorption coefficient, with a peak at its central wavelength from the Schrödinger equation solution. Spectral analysis reveals strategic enhancement in light absorption across visible and near-infrared regions, broadening the perovskite absorption range beyond 800 nm. These QDs enhance both infrared and visible spectra, improving light harvesting. Summing the absorption of single QD groups creates a continuous spectrum, enhancing perovskite film stability and morphology. Rigorous optical analysis and comprehensive electrical modeling investigate charge carrier interactions within the photovoltaic framework. The study verifies around 24 % efficacy enhancement compared to QD-absent configurations, surpassing uniformly dispersed QDs by 11 %. Optical and electrical analyses yield a short-circuit current of 26.7 mA/cm2, open-circuit voltage of 1.13 V, fill factor of 0.88, and overall efficiency of 25.12 % in superimposed configurations. Results underscore the significance of varied QD dimensions and layered structures for enhanced absorption, offering a promising route for advancing thin-film solar technology. The study showcases the potential of PbS CQDs with varying radii in photovoltaics, contributing to improved efficiency and stability, with implications for the future of solar energy technology.

B-site doping with bismuth ion enhances the efficiency and stability of inorganic CsSnI3 perovskite solar cell

B-site doping with bismuth ion (Bi3+) is adopted to enhance the quality and stability of CsSnI3 perovskite. The partial displacement of Sn2+ with Bi3+ can not only improve the morphology, crystallinity, and stability of CsSnI3 perovskite film, but also reduce the trap density of CsSnI3 perovskite. Consequently, the fabricated perovskite solar cell with Bi3+-doped CsSnI3 perovskite deliver a high power conversion efficiency of 6.11 %, which is increased by 77 % compared to the efficiency of the control cell. In addition, the device without any encapsulation preserves over 72 % of its initial efficiency after storage in ambient condition for 240 h.

Modulating the Photoresponsivity of Perovskite Photodetectors through Interfacial Engineering of Self‐Assembled Monolayers

AbstractPhotodetectors are one of the most essential optoelectronics nowadays. Perovskites have emerged as one of the potential materials for photodetectors due to their high absorption efficiency over a wide range of wavelengths, high charge mobility, strong mechanical deformability, and solution processability. In this study, interfacial engineering using self‐assembled monolayers (SAMs) is explored to improve the performance of perovskite photodetectors. SAMs with different terminal groups exhibit distinct surface energy, and they all result in a reduced exciton lifetime of the perovskite due to charge transfer between polycrystalline perovskite and the SAMs. In particular, the photodetector modified with (4‐hydroxyphenyl)phosphonic acid (OH) exhibits the highest electron mobility of 0.8 cm2 V−1 s−1 under 450‐nm light illumination. In addition, it shows excellent detector performance with an ultrafast photoresponse of < 14 ms, a high photoresponsivity of 5600 AW−1, and a high specific detectivity of 5.9 × 1010 Jones at a low light intensity of 18 µW cm−2. The excellent photoresponse and device switchability are attributed to the high surface energy of OH, the resulting homogeneous perovskite film morphology, the high charge transfer efficiency, and the favorable energy level alignment. The studies provide new prospects for the development of emerging perovskite photodetectors.

Ionic Liquid Additives for Efficient and Durable Two-Step Perovskite Photovoltaic Devices

Ionic liquids (ILs) have found widespread use in controlling the crystallization process of perovskites, optimizing the morphology and enhancing the device performance, especially in the one-step method. However, research regarding the effects of ionic liquids on perovskite devices prepared using the two-step method remains relatively scarce. Here, an IL 1-Hexyl-3-methylimidazolium Tetrafluoroborate (HMIMBF4) is selected as an additive in the perovskite precursor solution for the fabrication of PSCs using the two-step method. Our study involves a systematic exploration of the precise effects of ILs on the morphology of perovskite thin films, defect density, and photovoltaic performance. IL HMIMBF4 is convincingly shown to possess a robust chemical affinity with perovskite components, thereby establishing a basis for the inhibition of ion migration. Concurrently, ILs play a pivotal role in governing the morphology of perovskite while also facilitating the conversion of lead iodide into the perovskite structure. Benefiting from the regulation of the perovskite morphology and defect states by IL HMIMBF4, the devices with an efficiency exceeding 23% is ultimately achieved. Our research provides a comprehensive comprehension and contributes to advancing the utilization of ILs in two-step photovoltaic devices.

Improving Efficiency and Stability of p–i–n Perovskite Solar Cells by Capsaicin‐Based Antisolvent Additive Engineering

Improving the morphology and crystallinity of polycrystalline perovskite films is essential for perovskite solar cells (PSCs) with high efficiency and stability. Herein, capsaicin‐based antisolvent additive engineering (AAE) is proposed to fabricate MAPbI3‐based p–i–n PSCs by simply adding capsaicin into antisolvent to simultaneously regulate crystallization and passivate defects of perovskite films. Meanwhile, a more n‐type surface is formed by the spatially confined distribution of capsaicin at grain boundaries and top interfaces of perovskite induced by the proposed AAE process, which facilitates the transport of charge carriers. As a result, the MAPbI3‐based PSCs with p–i–n architecture achieve a high power conversion efficiency (PCE) of 20.85% with negligible hysteresis (active area of 0.07 cm2), as well as an improved stability by maintaining 70.7% of the initial PCE after monitoring for over 400 h under ambient environment (25%–35% relative humidity) without encapsulation. In this work, a facile and effective strategy is proposed to prepare high‐quality perovskite films, which improves the efficiency and stability of PSCs and paves the way for further commercialization of PSCs.

Hydrophobic poly-TPD modified PEDOT PSS surface for improved and stable photovoltaic performance of MAPbI3 based p-i-n perovskite solar cells

Inferior morphology of perovskite films and suppressed hole extraction restricts the performance of perovskite solar cells (PSCs) with a PEDOT:PSS hole transporting layer (HTL). In this work, poly-TPD is used to modify the surface of PEDOT:PSS films in PSC. The presence of hydrophobic poly-TPD decreases the nucleation sites, and as a result, perovskite films with larger grains are obtained. Improved energy level alignment in the presence of poly-TPD results in enhanced hole extraction from the perovskite layer to the HTL. The improved morphology and charge extraction resulted in improved photovoltaic performance. The power conversion efficiency (PCE) of PSCs was increased from 13.6% to 16.1% with the incorporation of poly-TPD. Also, the shelf life of the PSCs has exhibited considerable improvement due to the presence of hydrophobic poly-TPD and fewer number of grain boundaries. After 66 days, the PSC with poly-TPD maintained 96% of its initial PCE, whereas the PCE of the control device degraded to 72% of its initial value.