Power Conversion Efficiency Of Perovskite Solar Cells Research Articles

Wide spectral response perovskite solar cells mixed with NaGdF4:Yb3+, Er3+@NaGdF4:Eu3+ core-shell rare earth nanoparticles

In this study, NaGdF4:Yb3+, Er3+@NaGdF4:Eu3+ ([email protected]) core-shell rare earth nanoparticles are prepared by a simple hydrothermal method. After testing, the emission peaks are observed at 415, 525, 540 and 660 nm with an excitation light of 980 nm due to the up-conversion luminescence from rare-earth nanoparticles. Under light excitation at 395 nm, the rare-earth nanoparticles undergo down-conversion luminescence with emission peaks at 590, 610 and 695 nm. The resulting nanoparticles are introduced into the TiO2 mesoporous layer of hole-conductor-free perovskite solar cells (PSCs) based on carbon counter electrodes to broaden the spectral response of the cells from the visible range to the near-infrared and near-ultraviolet regions, which can guarantee a high light absorption efficiency and corresponding accelerated generation of electron-hole pairs. The results suggest that the mixing of [email protected] nanoparticles into mesoporous TiO2 layer improves the power conversion efficiency of PSCs to 14.21%, which is 10.6% higher than that of the control cells, which can pave an effective way to improve the performance of PSCs with a broadened response range.

Controlling the Defect Density of Perovskite Films by MXene/SnO2 Hybrid Electron Transport Layers for Efficient and Stable Photovoltaics

The defect control of polycrystalline perovskite films is essential for achieving an efficient and stable perovskite solar cell (PSC). However, existing methods of reducing defects suffer from their complex processes, low durability, and limited effects by using molecular materials in terms of passivation mechanisms. Herein, a hybrid film composed of SnO2 nanoparticles/Ti3C2Tx MXene nanoflakes is used as the electron transport layer (ETL) in a planar regular-structure PSC. The results indicate that by changing the Ti3C2Tx/SnO2 ratios (0–2.2 wt %) in ETLs, the film qualities of top perovskite layers are controllable, including the compactness, crystal size, surface roughness, crystallinity, optical absorption, defect density, and so forth. The defect density in perovskite films is substantially reduced from 5.65 × 1015 to 2.25 × 1015 cm–3 using an optimized hybrid ETL (1.4 wt %) compared with the pristine SnO2, while the electrical conductivity of the hybrid ETL is decreased probably due to the geometric factor of the incorporated MXene. As a result, the power conversion efficiency of PSCs is significantly increased from 16.28 to 20.35%, and the environmental stability of the unencapsulated devices is greatly improved. This work provides a facile, robust, and effective way to reduce defects in perovskite films by using emerging MXene nanomaterials and might also be useful to other perovskite-based (opto)electronic devices such as light-emitting diodes and photodetectors.

Laser induced core–shell liquid metal quantum dots for high-efficiency carbon-based perovskite solar cells

Metal particles with excellent conductivity can be used as additives to ameliorate the performance of perovskite solar cells (PSCs). However, it is formidable to generate stable liquid metal particles especially quantum dots because of the room-temperature fluidity. Herein, in this work, eutectic gallium-indium liquid metal quantum dots (GIQDs) were prepared via pulsed laser irradiation in anti-solvent and incorporated in perovskite film to accelerate electron transport due to the superior conductivity. As a result, the charge transport resistance was decreased, leading to the fast quenching effect and short carrier lifetime at the surface of perovskite film, which were verified by steady-state and time-resolved photoluminescence. Besides, the reduced charge recombination contributed to the enhancement of current density. Moreover, after the optimization of 0.1 mg/mL GIQDs incorporated in perovskite film, the power conversion efficiency of PSCs obtained a champion value of 15.55%, which improved 17.18% when compared with pristine samples of 13.27%. This article will pave the way for binary liquid metal synthesizing and optoelectronic applications.

Electron Beam Irradiation of Lead Halide Perovskite Solar Cells: Dedoping of Organic Hole Transport Materials despite Hardness of the Perovskite Layer.

Organic-inorganic lead halide perovskite solar cells (PSCs) are highly efficient, flexible, lightweight, and even tolerant to radiation, such as protons, electron beams (EB), and γ-rays, all of which makes them plausible candidates for use in space satellites and spacecrafts. However, the mechanisms of radiation damage of each component of PSC [an organic hole transport material (HTM), a perovskite layer, and an electron transport material (ETM)] are not yet fully understood. Herein, we investigated the EB irradiation effect (100 keV, up to 2.5 × 1015 cm-2) on binary-mixed A site cations and halide perovskite (MA0.13FA0.87PbI2.61Br0.39, MA:methylammonium cation and FA:formaminidium cation), a molecular HTM of doped SpiroOMeTAD, and an inorganic ETM of mesoporous TiO2. Despite the decreased power conversion efficiency of PSCs upon EB exposure, the photoconductivities of the perovskite, HTM, and ETM layers remained intact. In contrast, significant dedoping of HTM was observed, as confirmed by steady-state conductivity, photoabsorption, and X-ray photoelectron spectroscopy measurements. Notably, this damage could be healed by exposure to short-wavelength light, leading to a partial recovery of the PSC efficiency. Our work exemplifies the robustness of perovskite against EB and the degradation mechanism of the overall PSC performance.

Overcoming the performance deadlock by ideal-bandgap perovskites

Metal-halide perovskite solar cells (PSCs) have gained enormous attention because of their superior optoelectronic properties. Whereas currently most high-performance PSCs are based on 1.5–1.6 eV bandgap perovskites, which have a bottleneck problem for realizing the theoretically highest power conversion efficiency of PSCs, ideal-bandgap (1.3–1.4 eV) PSCs show great promise for addressing this issue. Recently in Matter, a complex additive SnCl2·3FACl for methylammonium-free ideal-bandgap perovskites was reported by Zhu, Zhou, Padture, and coworkers, affording a power conversion efficiency of near 20% with ultrahigh device stability and paving the way toward the Shockley-Queisser limit of PSCs.

Improving the efficiency of perovskite solar cells via embedding random plasmonic nanoparticles: Optical–electrical study on device architectures

Perovskite solar cells (PSCs) based on lead halide and solution process face issues such as low efficiency and high manufacturing costs. Recently, the emerging field of plasmonics as a branch of photonics has been utilized in electronic, optic and electro-optic devices, which deals with optical phenomena in metallic nanostructures like Au, Ag and Cu. One way to enhance the efficiency is the increase of absorbent layer thickness, while increasing the manufacturing cost. Here, we intend to examine the size, number, and composition of random plasmonic nanoparticles (RPNPs) in the active layer (AL) so that we can increase the power conversion efficiency (PCE) without changing the absorbent layer thickness. The simulation results demonstrate an improve in photocurrent of the device as much as 11.12% (18.24–20.27 mA/cm2) using the near-field plasmon-enhanced properties of RPNPs, while the number and radius of PNPs embedded in the AL are 50 and 10 nm, respectively. With Ag RPNPs, the photocurrent increases up to 16.5% (18.24–21.25 mA/cm2). Utilizing RNPNs is an efficient method for improving PCE in PSCs with thin absorption layer (up to 200 nm). Given the optimal parameters obtained for RPNPs, our study is very useful for the development of PSCs.

On the role of solution-processed bathocuproine in high-efficiency inverted perovskite solar cells

The s-shaped J-V curve of perovskite solar cells can be eliminated using the solvent penetration (SP) process with a PCBM spacer. The experimental results show that the viscosity of the solvent used in the SP process influences the shunt and series resistances simultaneously. In addition, the fill factor of PEDOT:PSS based perovskite solar cells can be largely increased from 40.3% to 70.7% when the bathocuproine (BCP) molecules are dissolved in IPA solvent during the SP process, which significantly increases the power conversion efficiency (PCE) by 98.9%. Besides, the PCE of perovskite solar cells increases from 13.56% to 20.29% when the PEDOT:PSS film is replaced by a P3CT-Na thin film. It is noted that the absorbance spectra, photoluminescence (PL) spectra, time-resolved PL, Raman spectra and X-ray diffraction patterns demonstrate that the BCP molecules penetrate into the PCBM thin film and the PCBM/perovskite interface during the SP process, which increases the electron mobility of the PCBM thin film and passivates the interfacial MA cations in perovskite thin film, respectively. In other words, the solution-processed BCP small molecules are vertically distributed across the PCBM thin film. Our results help completely understand the entire roles of the solution-processed BCP molecules in the high-performance inverted-type perovskite solar cells.

Synthesization and optical characterization of photovoltaic materials for perovskite solar cell application

The performance of Perovskite solar cells (PSCs) has rapidly increased over the last decade. The power conversion efficiency (PCE) of 25.2% has been reported. Drastic and rapid change in PCE of PSCs has attracted a lot of attention toward this alternative photovoltaic technology that can be manufactured using simple and low cost processing techniques, over the traditional silicon solar technology. Here in this work, we have synthesized Molybdenum trioxide (MoO3) and Titanium dioxide (TiO2) for charge transport materials application in PSC application. The analysis of materials has been carried out by photoluminescence and absorbance spectra. The results signify that MoO3 has absorbed at the visible region around (600-800) nm and the absorbance of TiO2 tuned at 400 nm. Due to high absorption range (600-800) at visible region MoO3 is suitable for Hole Transport Material (HTM). The widely used Electron Transport Material (ETM) TiO2 is also synthesized and characterized.

Synergistic Engineering of Natural Carnitine Molecules Allowing for Efficient and Stable Inverted Perovskite Solar Cells

Efficient control of the perovskite crystallization and passivation of the defects at the surface and grain boundaries of perovskite films have turned into the most important strategies to restrain charge recombination toward high-performance and long-term stability of perovskite solar cells (PSCs). In this paper, we employed a small amount of natural vitamin B (carnitine) with dual functional groups in the MAPbI3 precursor solution to simultaneously passivate the positive- and negative-charged ionic defects, which would be beneficial for charge transport in the PSCs. In addition, such methodology can efficiently ameliorate crystallinity with texture, better film morphology, high surface coverage, and longer charge carrier lifetime, as well as induce preferable energy level alignment. Benefiting from these advantages, the power conversion efficiency of PSCs significantly increases from 16.43 to 20.12% along with not only a higher open-circuit voltage of 1.12 V but also an outstanding fill factor of 82.78%.

How Does Bridging Core Modification Alter the Photovoltaic Characteristics of Triphenylamine-Based Hole Transport Materials? Theoretical Understanding and Prediction.

Perovskite solar cells have gained immense interest from researchers owing to their good photophysical properties, low-cost production, and high power conversion efficiencies. Hole transport materials (HTMs) play a dominant role in enhancing the power conversion efficiencies (PCEs) and long diffusion length of holes and electrons in perovskite solar cells. In hole transport materials, modification of π-linkers has proved to be an efficient approach for enhancing the overall PCE of perovskite solar cells. In this work, π-linker modification of a recently synthesized H-Bi molecule (R) is achieved with novel π-linkers. After structural modifications, ten novel HTMs (HB1-HB10) with a D-π-D backbone are obtained. The structure-property relationship, and optoelectronic and photovoltaic characteristics of these newly designed hole transport materials are examined comprehensively and compared with reference molecules. In addition, different geometric parameters are also examined with the assistance of density functional theory (DFT) and time-dependent DFT. All the designed molecules exhibit narrow HOMO-LUMO energy gaps (Eg =2.82-2.99 eV) compared with the R molecule (Eg =3.05 eV). The designed molecules express redshifting in their absorption spectra with low values of excitation energy, which in return offer high power conversion efficiencies. Further, density of states and molecular electrostatic potential analysis is performed to locate the different charge sites in the molecules. The reorganizational energies of holes and electrons are found to have good values, suggesting that these novel designed molecules are efficient hole transport materials for perovskite solar cells. In addition, the low binding energy values of the designed molecules (compared with R) offer high current charge density. Finally, complex study of HB9:PC61 BM is also undertaken to understand the charge transfer between the molecules of the complex. The results of all analyses advocate that these novel designed HTMs are promising candidates for the construction of future high-performance perovskite solar cells.

Progress in blade-coating method for perovskite solar cells toward commercialization

The hybrid organic–inorganic halide perovskite solar cells (PSCs) have attracted considerable attention in the photovoltaic community during the last decade due to unique properties, such as high absorption coefficient, solutionable fabrication, and compatibility with roll-to-roll technology. A certified power conversion efficiency of PSCs as high as 25.2% has been obtained, approaching the levels of silicon solar cells, copper indium gallium selenide (CIGS), and cadmium telluride (CdTe) thin-film solar cells. However, the device area of a PSC is one of the biggest challenges for the commercialize applications. To fabricate large-area PSCs, various fabrication methods have been proposed, including spray coating, slot-die coating, vacuum deposition, and blade coating. Here, the blade-coating technique progress for the PSC fabrication has been reviewed. Moreover, the optimized ways during the solution fabrication process, the efficient strategy for improving the perovskite films' morphology, have also been summarized in this work. In the last part, the challenges and opportunities of PSC commercialization have also been proposed.

High stability perovskite solar cells under ambient conditions

Though perovskite solar cells have outstanding commercialisation potential, perovskite materials are very vulnerable to moisture and oxygen. So the main issue for perovskite solar cell is very fast degradation. In order to elaborate on this concern, the stability of perovskite solar cells were investigated in this study. The effect of oxygen and moisture on perovskite solar cells decreased with encapsulation of the cells. Encapsulation has been carried out with ultraviolet cured epoxy resin. Stability tests were taken place in laboratory conditions under solar simulator and also shelf-life tests. Perovskite solar cells showed the highest power conversion efficiency (PCE) of 9.77% with a short circuit current density of 22.5 mA/cm2, the open-circuit voltage of 0.94 V and fill factor of 0.46. After 2800 h, perovskite solar cells were still 85% stable in atmospheric conditions. Perovskite solar cells exhibited distinctive durability for shelf-life test in laboratory conditions. The PCE of perovskite solar cells were decreased only 15% of its initial value after 2800 h. In order to elaborate the degradation of perovskite solar cells, the cells are exposed to solar irradiation AM1.5G. Perovskite solar cells degraded gradually with time under solar irradiation; however, this stability test indicated that the solar cells were durable 20% after 500 h exposure to solar irradiation.

Influence of the Quality of SnO2 Electron Transport Layer on the Stability of FA1-XCsxpb(I1-yBry)3 perovskite Layer

Organic-inorganic lead halide perovskites have attracted great attention as light absorbers of hybrid perovskite solar cells (PSCs). Among the organic-inorganic hybrid perovskites (OIHP), CH3NH3PbI3 (MAPbI3) and CH(NH2)2PbI3 (FAPbI3) have been extensively studied as light absorbers of PSCs. PSCs are expected to be next-generation solar cells due to their high conversion efficiency and low fabrication cost. However, power conversion efficiency of PSCs declines shortly after being fabricated, because of degradation of hybrid perovskite layers. OIHP such as FAPbI3 decomposes easily into PbI2 and transforms to d-phase from a-phase, which is suitable for the application to the solar cells, under ambient condition [1]. It was reported that partial substitution of inorganic monovalent ions such as Cs and Rb ions at FA site is effective to improve the phase stability of a-phase [2]. This can be easily explained by the Goldschmidt tolerance factor [3], which is an indicator for the stability of perovskite structure. Ionic radius of FA is too large, but the partial substitution of Cs or Rb can make the average ionic radius smaller than that of FA, which stabilizes the a-phase. For example, d-phase is the stable phase in FAPbI3 at ambient condition, which transforms to a-phase above 165 ℃ [4]. However, the partially substituted FAxCsyPbI3 is stable even at room temperature. The perovskite layers are grown on electron transport layers (ETL) such as TiO2, SnO2, and ZnO by spin-coating method. Although TiO2 has been widely used for ETL of PSCs, SnO2 has been also applied to ETL because of its excellent band energy level alignment with that of the perovskite layers and its higher electron mobility [5]. In addition, devices using SnO2 as ETL decrease their photoconversion efficiency more slowly than using TiO2 under ambient condition, which suggests that decomposition processes of the perovskites on TiO2 and SnO2 is different [6]. In the fabrication process of ETL, SnO2 is annealed after spin-coating. If the annealing temperature is high above 450 degrees Celsius, rutile structured crystalline SnO2 thin film grows, while only amorphous structured SnO2 thin film appear by the low temperature annealing, such as between 150 and 200 degrees Celsius. Some studies have shown that amorphous SnO2 fabricated by low temperature process increases performances of devices compared with crystalline SnO2 [7, 8].In this study, FA1-xCsxPb(I1-yBry)3 was synthesized by spin-coating method on the SnO2 layers and annealed at various temperature to evaluate the dependence of SnO2 substrate structure on the stability of perovskite layers. Stability of all the samples here synthesized were monitored with the X-ray diffraction technique at 0, 1, 2, 3, 4, 24, 96 and 168 hours kept in air after fabrications. Fig.1 shows the intensity of diffraction peaks of d-FAPbI3 (100) as a function of time. Although the intensity of d-FAPbI3 peaks increased in FA0.85Cs0.15PbI3 and FA0.85Cs0.15Pb(I0.85Br0.15)3 formed on SnO2 annealed at 450 ℃ , it unchanged in FA0.85Cs0.15PbI3 and FA0.85Cs0.15Pb(I0.85Br0.15)3 on SnO2 annealed at 180 degree Celsius. These results sugessts that the stability of a-FAPbI3 grown on SnO2 annealed at 180 degree Celsius is better than that annealed at 450 degree Celsius. The crystal structures of SnO2 annealed at 200, 300 and 400 degree Celsius were characterized with the Glazing Incident X-ray diffraction technique. The surface morphology of SnO2 were obsereved with the scannning electron microscope, which suggest SnO2 surface became rougher as annealing temperature increased. The chemical composition of the surface of SnO2 layers were investigated by Auger electron spectroscopy, from which Cl peaks were obsererved in SnO2 annealed at 200 ℃ and 300 ℃, while Cl were not detected in SnO2 annealed at 400 degree Celsius.[1] T. Leijtens et al., J. Mater. Chem. A.5, 11483-11500 (2017)[2] M. Saliba et al., Science 354, 206-209 (2016)[3] C. C. Stoumpos et al., Acc. Chem. Res. 48, 2791-2802 (2015)[4] Z. Li et al., Chem. Mater. 28, 284-292 (2016)[5] L. B. Xiong et al., J. Mater. Chem. A.4, 8374-8383 (2016)[6] Q. Dong et al., Nano Energy 40, 336-344 (2017)[7] W. J. Ke et al., J. Mater. Chem. A.3, 24163-24168 (2015)[8] K.-H Jung et al., J. Mater. Chem. A.5, 24790-24803 (2017) Figure 1

A sulfur-rich small molecule as a bifunctional interfacial layer for stable perovskite solar cells with efficiencies exceeding 22%

Abstract Remarkable progress has been made in perovskite solar cells (PSCs) recently. However, the defects present in the perovskite layer act as non-radiative recombination centers to decrease the stability and restrict the further performance improvement of the device. We report herein a sulfur-rich two-dimensional small molecule, SMe-TATPyr, as a bifunctional layer to efficiently passivate the surface defects of perovskite and facilitate the hole transfer at the perovskite/spiro-OMeTAD interface. X-ray photoelectron spectroscopy analyses show that the sulfur atoms of SMe-TATPyr can passivate the uncoordinated Pb2+ defects and suppress the Pb0 defect formation as Lewis bases. As a result, the power conversion efficiency of PSCs is distinctly increased from 20.4% to 22.3%. Moreover, this simple interfacial modification could effectively enhance the stability of unencapsulated PSCs to retain 95% of the initial efficiency after storage for 1500 h at ambient conditions, in contrast to 70% efficiency retention of the device without SMe-TATPyr under the same conditions.

Two-Step Processed Efficient Potassium and Cesium-Alloyed Quaternary Cations Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (PSCs) are continuously attracting much attention due to the poential applications in low-cost and flexible solar energy system. In this work, potassium (K+) and cesium (Cs+) were added into the perovskite (FAMA)Pb(IBr)3 (FA = CH(NH2)2+, MA = CH3NH3+) to prepare the high-quality quadruple-cation (KCsMAFA) perovskite film and PSCs via two-step solution process. The optoelectronic properties and stability of FAMA, CsFAMA and KCsFAMA perovskite film and PSC devices were systematically studied and analyzed. The power conversion efficiency (PCE) of champion KCsFAMA device reached 19.70%, and the steady output PCE was 19.40% with a simple device structure of ITO/SnO2/Perovskite/Spiro-OMeTAD/Ag. In addition, the stability of PSCs with quadruple-cation KCsMAFA was significantly improved as compared to the control ones. With the storage in air for 20 days (humidity ∼35%), the PCEs of PSCs without encapsulation could maintain 77% of the initial values, while the PCEs of PSCs with MAFA and CsMAFA only maintained 39% and 56% of their initial values, respectively. The improved efficiency and stability in PSCs with both K+ and Cs + were attributed to significant improvement in the film quality with large and dense grains, which could reduce grain boundaries and moisture immersion. Meanwhile, the incorporation of K+ and Cs+ could enhance the charge transfer resistance and suppress the charge recombination effectively, supporting in the improvement in the performance of PSCs.

Optimizing the working mechanism of the CsPbBr3-based inorganic perovskite solar cells for enhanced efficiency

Recently, inorganic perovskite solar cells (PSCs) based on CsPbBr3 have triggered incredible interest due to the demonstrated excellent stability against thermal and high humidity environmental conditions. However, the power conversion efficiency (PCE) of the CsPbBr3-based PSCs is still lower than that of the organic-inorganic hybrid one, because of the large band gap and serious charge recombination at the interface or inside the device. Here, the working mechanism of the devices with normal n-i-p planar structure is modeled and investigated using SCAPS 1D simulation software. The simulation results state that the proper band structure of PSCs is crucial to carrier separation and transport. The high interface recombination, originated from the large band offsets of the electron transport material (ETM)/absorber and absorber/hole transport material (HTM) respectively, can be effectively diminished with the continuous gradient junction design of the absorber, and a PCE of 11.58% is obtained with a high open-circuit voltage (VOC) of 1.68 V. Moreover, by building a heterojunction bilayer absorption scenario of CsPbIBr2/CsPbBr3 and employing ZnOS and Cu2ZnSnS4 films as the ETM and HTM respectively, the PCE of PSCs is further increased to 15.89%, caused mainly by the enhancement in short-current density (JSC). Moreover, reducing the interface defect density is also very important to improve the performance of PSCs. These results will provide theoretical guidance for improving the performance of the CsPbBr3-based PSCs.

Investigation of p-type SnO films served as a potential hole-transporting material for highly efficient perovskite solar cells

As an essential component of perovskite solar cells (PSCs), the design of hole transport materials (HTMs) has always been a topic of interest in the photovoltaic community. In this work, p-type tin monoxide (SnO) films are grown by electron beam evaporation to investigate the influence of substrate temperature and deposition time on their properties. The film crystallization and preferred growth orientation of (001) showed prominent enhancement with the increase in substrate temperature. The prolongation of deposition time witnessed changes in grain morphology from nanoparticles to nanosheets. Hall measurements revealed that the film deposited at 200 °C showed the lowest resistivity, the maximum carrier concentration, and the lowest carrier mobility. Using these films as HTMs, the performance of PSCs based on caesium lead iodide perovskites (CsPbI3) was analyzed theoretically and experimentally, and high open-circuit voltage (VOC) of 1.16 V is obtained. With the increase of the substrate temperature, the power conversion efficiency of PSCs is decreased due to the decreased hole concentration. The results suggest that SnO film deposited at low substrate temperature holds promise for facilitating high-performance PSCs as HTMs.

Improved the Performance and Stability at High Humidity of Perovskite Solar Cells by Mixed Cesium-Metylammonium Cations

Perovskite solar cells have a great potential as competitor of silicon solar cells which have been dominated the market of solar cells since last decade, due to a tremendous improvement of their power conversion efficiency (PCE). Recently, a PCE of perovskite solar cells above 23% have been obtained. Moreover, perovskite solar cells can be fabricated using simple solution methods, therefore, the whole cost production of solar cells is less than half of silicon solar cells. However, their low stability in thermal and high humidity hinder them to be produced and commercially used to replace silicon solar cells. Many efforts have been done to improve both PCE and stability, including mixed inorganic-organic cations, mixed halide anions, improvement of perovskite morphology or crystallinity and using small molecules for passivation of defect in perovskite. In this paper, we used mixed cesium-methylammonium to improve both PCE and stability of perovskite solar cells. Cesium was used due to its smaller ionic radius than methylammonium (MA) ions, therefore, the crystal structure of perovskite is not distorted. Moreover, perovskite cesium-lead-bromide (CsPbBr3) are more stable than that of MAPbBr3 and doping cesium increased light absorption in perovskite MAPbBr3. We studied the effect of mixed cesium-MA on the PCE and stability at high humidity (>70%). The percentage of cesium was varied at 0%, 5%, 10%, 15% and 20%. The perovskite solar cells have monolithic hole-transport layer free (HTL-free) structure using carbon as electrode. This structure was used due simple and low cost in processing of solar cells. Our results showed that by replacing 10% of MA ions with Cs ions, both PCE and stability at high humidity are improved.

Tailoring the orientation of perovskite crystals via adding two-dimensional polymorphs for perovskite solar cells

Organic-inorganic perovskite materials are attracting increasing attention for their use in high-performance solar cells due to their outstanding properties, such as long diffusion lengths, low recombination rate, and tunable bandgap. Finding an effective method of defect passivation is thought to be a promising route for improvements toward narrowing the distribution of the power conversion efficiency (PCE) values, given by the spread in the PCE over different devices fabricated under identical conditions, for easier commercialization. In this work, we add 2‐(4‐fluoroph-enyl)ethyl ammonium iodide (p-f-PEAI) into the bulk of a mixed cation lead halide perovskite (CH3NH3PbBr3)0.15(HC(NH2)2PbI3)0.85 thin film. We investigate the influence of different p-f-PEAI concentrations on the optical properties, morphology, crystal orientation, charge carrier dynamics, and device performance. We observe that introducing the proper amount of p-f-PEAI changes the preferential orientation of the perovskite crystals, promotes the strength of the crystal textures, and suppresses non-radiative charge recombination. Thus, we obtain a narrower distribution of the PCE of perovskite solar cells (PSCs) without sacrificing the PCE values reached. This is an important step toward better reproducibility to realize the commercialization of PSCs.

Performance improvement of perovskite solar cells via spiro-OMeTAD pre-crystallization

Meticulous choice of hole transport materials (HTMs) is a crucial factor for carrier extraction and device stability in solar cells. 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) as a HTM is a milestone in the development of perovskite solar cells (PSCs). Here, the photovoltaic performance of perovskite solar cells (PSCs) was improved by solvent treatment of spiro-OMeTAD film processed from non-benzene solvent (ethyl acetate). This treatment results in the pre-crystallization of spiro-OMeTAD, and thus an increased conductivity of the spiro-OMeTAD film. Via the solvent-treatment time, the highest power conversion efficiency of PSCs is improved to ~ 19%, accompany with the enhancements of short-circuit current, open-circuit voltage, and fill factor. These improvements attribute to the reduced carrier accumulation and decreased serial resistance at the perovskite/spiro-OMeTAD interface. Thermal stability and lifetime of the PSCs based on the pre-crystallization spiro-OMeTAD are also improved. This solvent treatment to adjust the spiro-OMeTAD crystallization offers a facile yet effective way to fabricate high conduction layers toward environmentally friendly PSCs.