Mixed-cation Perovskite Solar Cells Research Articles

Multi-Functional Regulation on Buried Interface for Achieving Efficient Triple-Cation Perovskite Solar Cells.

Mixed-cation perovskite solar cells (PSCs) have attracted much attention because of the advantages of suitable bandgap and stability. It is still a challenge to rationally design and modify the perovskite/tin oxide (SnO2) heterogeneous interface for achieving highly efficient and stable PSCs. Herein, a strategy of one-stone-for-three-birds is proposed to achieve multi-functional interface regulation via introducing N-Chlorosuccinimide (NCS) into the solution of SnO2: i) C═O functional group in NCS can induces strong binding affinity to uncoordinated defects (oxygen vacancies, free lead ions, etc) at the buried interface and passivate them; ii) incomplete in situ hydrolysis reactions can occur spontaneously and adjust the pH value of the SnO2 solution to achieve a more matchable energy level; iii) effectively releasing the residual stress of the underlying perovskite. As a result, a champion power conversion efficiency (PCE) of 24.74% is achieved with a device structure of ITO/SnO2/Perovskite/Spiro-OMeTAD/Ag, which is one of the highest values for cesium-formamidinium-methylammonium (CsFAMA) triple cation PSCs. Furthermore, the device without encapsulation can sustain 94.6% of its initial PCE after the storage at room temperature and relative humidity (RH) of 20% for 40 days. The research provides a versatile way to manipulate buried interface for achieving efficient and stable PSCs.

Critical role of dopant in NiOx hole transport layer for mitigating redox reactivity at NiOx/absorber interface in mixed cation perovskite solar cells.

Redox chemistry transpiring at the interface of NiOx hole transport layer (HTL) and perovskite absorber is a critical phenomenon leading to relatively low values of open circuit voltage (VOC) and fill factor (FF), in turn hampering the overall device performance and stability. In this work, for the first time, the hard acid electronic nature of vanadium (V) dopant in nickel oxide HTL is opportunely exploited to mitigate the undesirable Lewis acid-base reactions occurring at the HTL/mixed-cation perovskite interface. The findings of the study show that vanadium doping results in improved interfacial energetics along with decreased VOC loss, confirming that despite the increase in Ni3+/Ni2+ ratio with the vanadium dopant, the redox reaction catalyzed by Ni3+ ions is kept under check. Vanadium doping also aided in the realization of superior perovskite films with lower Urbach energy, which translated into one order increase in maximum photoinduced carrier generation rate per unit volume. Carrier dynamics investigations show fewer defect states (lower VTFL) and trap-assisted recombination (lower diode ideality factor), which optimize the devices' photovoltaic performance. These benefits collectively contribute to low-loss charge transfer across the NiOx/mixed-cation perovskite interface, which increases the relative efficiency by ∼30% for 5 wt% V-doped NiOx devices compared to pristine NiOx devices, augmented by an increase in device J-V parameters like open circuit voltage (VOC), short circuit current density (JSC), and fill factor (FF).

Effect of electron irradiation on perovskite films and devices for novel space solar cells

Perovskite solar cells (PSCs) are considered as one of the strong contenders for next-generation space solar cells due to their advantages of high efficiency, low cost, high specific power, and remarkable irradiation resistance compared with those of silicon-based and III-V compound solar cells. At present, one focuses on the irradiation effects of perovskite solar cells, but there are a few studies on the irradiation damage mechanism of the core perovskite film. To advance the spatial application of perovskite solar cells, this study conducts a comprehensive examination of the performance fluctuations exhibited by mixed-cation perovskite films and solar cells under electron irradiation. Initially, the Monte Carlo method is employed to simulate and predict the effect of electron irradiation on perovskite solar cells. Subsequently, in conjunction with the microstructure characterization and the comparison of optical/electrical performance of perovskite films before and after irradiation, the irradiation damage mechanism of film is elucidated and the electron irradiation reliability of perovskite solar cells is evaluated. The research demonstrates that mixed-cation perovskite film and solar cells exhibit outstanding resistance to electron irradiation. Even when exposed to 100 keV electron irradiation with a cumulative fluence of 5×10<sup>15</sup> e·cm<sup>–2</sup>, the PSCs maintain an average power conversion efficiency of 17.29%, retaining approximately 85% of their initial efficiency. This study provides sound theoretical and experimental evidence for designing the irradiation-resistant reinforcement of new-generation space solar cells, contributing to the improvement of their operational performance and reliability in space applications.

Temperature behaviour of mixed-cation mixed-halide perovskite solar cells. Analysis of recombination mechanisms and ion migration

In our study, we show that compositional engineering of the “A” site cation of ABX3 perovskite structure formed by a mix of organic and inorganic cations is an effective route to improve the thermal stability of perovskite solar cells (PSCs). In this work, mixed-cation mixed-halide PSCs have been fabricated and characterized with temperature, from 253 up to 333 K. The active layer based on CsRbFAMAPb(IBr)3 results in a more stable device compared to standard MAPbI3 devices. Electrical characterization reveals a decrease of the solar cell parameters with temperature. Using Impedance Spectroscopy (IS) characterization, we have estimated an activation energy for the halide ion migration of 0.63 ± 0.08 eV, an ion diffusion coefficient of 10−14 cm2 s−1, and a defect density of 7.27·1015 cm−3. To our knowledge, this is the first time that these parameters have been calculated in CsRbFAMAPb(IBr)3 based devices, resulting in improved values compared to MAPbI3 devices. The worsening of device performance for temperatures above 300 K is attributed to a decrease of the spiro-OMeTAD conductivity and the degradation of the perovskite/spiro-OMeTAD interface. It is shown that for low temperatures (from 253 to 323 K), Shockley-Red-Hall (SRH) recombination in the bulk governs, while for temperatures above 323 K the increase in surface recombination becomes dominant due to the presence of non-selective contacts. Numerical simulations using SILVACO ATLAS corroborate the role of SRH in the perovskite active layer for low and medium temperatures, and the crucial influence of spiro-OMeTAD transport properties in the device performance parameters.

Heterocyclic Functionalized Donor-Acceptor Hole-Transporting Materials for Inverted Perovskite Solar Cells.

Hole transport materials (HTMs) with appropriate energy levels and comprehensive passivation effects help to obtain highly efficient and stable perovskite solar cells (PSCs). Electron-deficient character-induced HTMs can generate varying energy level alignments near the HTM/perovskite interface. Herein, we report the synthesis and investigation of two new dipolar HTMs, WWC103 and WWC105, based on 2-(1,1-dicyanomethylene)rhodamine and 4-cynophenylacetonitrile acceptors, enabling high-efficiency mixed-cation mixed-halide perovskite solar cells. Apart from having different acceptors, these HTMs are built on a heterocyclic frame, which can provide passivation effects and improve the morphology of the perovskite layer. As a result, these dopant-free HTM-based solar cells show a high open-circuit voltage and good power conversion efficiency. Among both, the solar cell based on the HTM with 2-(1,1-dicyanomethylene)rhodamine exhibits a high open-circuit voltage of 1.09 V with a champion power conversion efficiency of over 20.51%. The improved performance of WWC103 over WWC105 (19.74%) is attributed to the new acceptor, which, in addition to providing good energy-level alignments and hole mobility, also holds the ability to passivate the defects. The findings suggest a new acceptor unit for constructing dopant-free HTMs for efficient PSCs.

Synergistic strategy of rubidium chloride regulated SnO2 and 4-tert-butyl-benzylammonium iodide passivated MAxFA1-xPbI3 for efficient mixed-cation perovskite solar cells

Nowadays, the MA-FA mixed-cation perovskite solar cells (PSCs), demonstrating much higher stability than that of single-cation MAPbI3 or FAPbI3, are still encountering a low-efficiency issue. The main reason is that there existing a lot of defects in SnO2 electron transport layers (ETLs) and perovskite absorbers. Herein, we develop a synergistic strategy of Rubidium Chloride (RbCl) doping and 4-tert-butylbenzylammonium iodide (tBBAI) passivation to fabricate high-performance MAxFA1-xPbI3 mixed-cation PSCs. The alkali halide RbCl is first selected as a novel doping additive to regulate the film properties of SnO2 and perovskites. Research shows that the negative Cl- ions can combine with uncoordinated Sn4+ ions due to their strong bonding ability, which can passivate the oxygen-vacancy-related defects and enhance the charge transport of SnO2 ETLs. Meanwhile, the doped Rb+ and Cl- ions may diffuse into perovskite lattices to promote grain growth and reduce the defects of perovskites. Besides, we employ an organic halide salt tBBAI to passivate perovskites and suppress surface defects. Results of deep level transient spectroscopy (DLTS) indicate that SnO2 and SnO2-RbCl based devices have deeper hole traps and large trap densities (ΔE = 0.92 eV, NT = 1.10 × 1016 cm−3; ΔE = 0.93 eV, NT = 2.16 × 1015 cm−3); while tBBAI-treated SnO2-RbCl-based devices own a shallower hole trap and a smaller trap density (ΔE = 0.72 eV, NT = 2.44 × 1013 cm−3); and the corresponding IPb and I(MA/FA) antisite defeats are also identified. Therefore, our synergistic strategy is effectively able to reduce the defect density and suppress the non-radiative recombination. Consequently, the best-performance MA0.85FA0.15PbI3 PSCs achieve an impressive power conversion efficiency (PCE) of 22.54% with a large open circuit voltage (Voc) of 1.16 V, which are by far the highest values of MA0.85FA0.15PbI3 mixed-cation PSCs.

IPL-Annealed Mixed-Cation Perovskites with Robust Coating Window toward Scalable Manufacturing of Commercial Perovskite Solar Cells

Perovskite solar cells (PSCs) are a promising alternative solar technology, but the technical challenges of (1) stability/durability, (2) efficiency at scale, and (3) manufacturability must be overcome to achieve widespread PSC commercialization. The challenge of balancing solution ink formulation and scalable manufacturing is often overlooked in the literature, where focus is on adopting inks from processes that will not scale. In this study, we apply a classical roll-to-roll manufacturing perspective, utilizing both compositional engineering and intense pulsed light (IPL) annealing, to develop a mixed-cation perovskite ink with a robust coating window that simultaneously solve issues of stability and manufacturability for PSCs. Our method resulted in blade-coated, flexible, mixed-cation PSCs on ITO-PET substrates with a champion power conversion efficiency (PCE) efficiency of 16.7% using IPL annealing of the absorber layer and, to our knowledge, is one of the fastest processing methods for the perovskite layer. This overall reduction in processing time with a stable ink represents an advance toward the scaled production of perovskite solar cells on flexible substrates.

Metal Halide Perovskite Surfaces with Mixed A‐Site Cations: Atomic Structure and Device Stability

AbstractMixing cations in the perovskite structure has been shown to improve optoelectronic device performance and stability. In particular, CsxMA1‐xPbBr3 (MA = CH3NH3) has been used to build high‐efficiency light‐emitting diodes. Despite those advantages, little is known about the exact location of the cations in the mixed perovskite film, and how cation distribution affects device properties and stability. By using scanning tunneling microscopy , the exact atomic structure of the mixed cation CsxMA1‐xPbBr3 perovskite interface is revealed. In addition, X‐ray photoelectron spectroscopy, ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy are used to study the stability and electronic properties of the CsxMA1‐xPbBr3 perovskite film. Partial substitution of MA+ by Cs+ induces a modification of the perovskite surface structure, leading to improved device stability is shown. These results provide a better understanding of the key parameters involved in the stability of mixed cation perovskite solar cells.

Passivation and energy-level change of the SnO2 electron transport layer by reactive titania for perovskite solar cells

Reactive anatase titania (TAc) are incorporated into SnO2 to form a single TAc-SnO2 electron transport layer (ETL) for mixed-cation perovskite solar cells (PSCs). The TAc-SnO2 layer is prepared in a low-temperature process by the advantage of high crystallinity and surface reactivity of TAc. The influence and mechanism of the TAc incorporation on the photovoltaic performance of PSCs are investigated. The TAc-SnO2 ETL presents rapid electron transfer, low trap density, high charge recombination resistance, low hysteresis and good stability. The 2.5-wt% TAc incorporation reveals the highest power conversion efficiency of 20.12 %, a 19 %-fold enhancement compared to the pristine cell with the SnO2 ETL. The enhancement arises from the fact that the TAc can fill up breaching in the pristine SnO2 layer and adjust the ETL energy level. The carboxyl groups of TAc facilitate the formation of solid bonding among SnO2/TAc colloids and prevent ions from accumulation at the interface of ETL/perovskite. The work provides a facile way to fabricate a low-temperature, single-layer and effective ETL for highly efficient PSCs.

LiI doping of mixed-cation mixed-halide perovskite solar cells: Defect passivation, controlled crystallization and transient ionic response

We investigate lithium iodide (LiI) doping of mixed-cation mixed-halide (MCMH) perovskites as a method to improve film morphology and optoelectronic properties, reduce defect-related recombination losses and limit ion migration. The optimized Li-doped devices achieved 21.5% power conversion efficiency (PCE) compared to 20.4% for undoped control devices. Furthermore, optimized Li-doped devices show minimized current-voltage hysteresis across a wide range of scan rates compared to control devices, which displayed significant scan-rate dependent hysteresis. We show, using a combination of experimental analysis and numerical device simulations, that the improved device performance and transient response at optimum doping concentration are consistent with reduced non-radiative recombination in the perovskite. However, increasing the LiI dopants beyond the optimum concentration alters the ionic properties of the perovskite absorber and changes the transient response. We also find that LiI addition results in a downward shift of the valence band and a corresponding transition from a weakly n-type to p-type perovskite material. These findings reveal the beneficial role of LiI dopant at low concentrations can improve shelf-life and minimize recombination-active defects, which are favourable for designing high-performance and stable mixed-cation mixed-halide perovskite devices.

Halide Remixing under Device Operation Imparts Stability on Mixed‐Cation Mixed‐Halide Perovskite Solar Cells

Mixed-halide mixed-cation hybrid perovskites are among the most promising perovskite compositions for application in a variety of optoelectronic devices due to their high performance, low cost, and bandgap-tuning capabilities. Instability pathways such as those driven by ionic migration, however, continue to hinder their further progress. Here, an operando variable-pitch synchrotron grazing-incidence wide-angle X-ray scattering technique is used to track the surface and bulk structural changes in mixed-halide mixed-cation perovskite solar cells under continuous load and illumination. By monitoring the evolution of the material structure, it is demonstrated that halide remixing along the electric field and illumination direction during operation hinders phase segregation and limits device instability. Correlating the evolution with directionality- and depth-dependent analyses, it is proposed that this halide remixing is induced by an electrostrictive effect acting along the substrate out-of-plane direction. However, this stabilizing effect is overwhelmed by competing halide demixing processes in devices exposed to humid air or with poorer starting performance. The findings shed new light on understanding halide de- and re-mixing competitions and their impact on device longevity. These operando techniques allow real-time tracking of the structural evolution in full optoelectronic devices and unveil otherwise inaccessible insights into rapid structural evolution under external stressconditions.

Thermally induced failure mechanisms in double and triple cations perovskite solar cells

The control of the cation composition of formamidinium (FA), methylammonium (MA), and cesium (Cs) has been used to engineer significant improvements in organic–inorganic perovskite solar cells. However, the thermal stability of mixed-cation perovskite solar cells is not fully understood. In this work, we present the results of an experimental study of the stability of double-cation perovskites [(FAPbI3)0.97(MAPbBr3)0.03] [(FAMA)-perovskite solar cells (PSCs)] and triple-cation based-perovskites [Cs0.05(FA0.95MA0.05)0.95Pb(I0.95Br0.05)3] [(CsFAMA)-PSCs] operated between 40 and 60°C. The thermally induced changes in the film microstructure are elucidated via scanning electron microscopy and x-ray diffraction analyses, and these are related to changes in optoelectronic properties, charge transport, and current–voltage characteristics of (FAMA)-PSCs and (CsFAMA)-PSCs. The implications of the observed degradation mechanisms are also discussed for the future development of efficient and stable PSCs.

Property degradation of mixed-cation perovskite films and solar cells irradiated with protons

This study reports on the proton irradiation-induced property degradation in Cs0.01MA0.01FA0.98PbI3 [MA = CH3NH3+, FA = CH(NH2)2+] perovskite films and solar cells (PSCs). Both 100 keV and 2 MeV protons are employed for irradiation. It is found that the threshold fluence for degradation of photovoltaic properties in PSCs is between 1 × 1013 and 1 × 1014 p/cm2 for 100 keV proton irradiation, or between 1 × 1014 and 2.2 × 1015 p/cm2 for 2 MeV proton irradiation. The degradation leads to a significant decrease in the short-circuit current; the open-circuit voltage is reduced to a less extent probably because of an increase in the electrical resistance across the interface between the perovskite and carrier transport layers. Irradiation-induced decomposition of CsMAFAPbI3 to PbI2 is observed due to the electronic energy deposition (radiolysis). With increasing proton fluence, the top Au electrode layer is finally exfoliated from the underlying spiro-OMeTAD layer, which could be attributed to the volume deformation of the spiro-OMeTAD induced by the accumulation of the gaseous products of perovskite decomposition.

Improved Stability of FAPbI3-Based Mixed-Cation Perovskite Solar Cells Fabricated Using Facile Cation Injection Technology

Compositional engineering adding organic and inorganic cations is considered one of the effective ways to improve the optoelectronic performance of PSCs. However, investigations of mixed-cations in PSCs are still a nascent area of research. In this study, an anti-solvent suitable for the preparation of mixed- cation perovskite was first adopted. We presented a simple surface engineering technique for manufacturing mixed-cation perovskite by injecting cations through the process of post-treatment of the adopted anti-solvent treated pure FAPbI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> film with methylammonium iodide (MAI) solution. The prepared mixed-cation perovskite film showed uniform particle size, particle growth, and significantly improved short-circuit current, charge coefficient, device efficiency and device stability.

Enhanced proton irradiation resistance in Cs-doped CH3NH3PbI3 films and solar cells

Mixed-cation perovskite solar cells have attracted tremendous attention in space applications due to their excellent power conversion efficiency (PCE) and stability to light and heat. Although the evolution of photovoltaic performance in different space environments has been investigated, the role of inorganic cesium ions (Cs+) in the enhancement of irradiation resistance needs to be further clarified. Herein, the structure and performance evolution of Cs-doped CH3NH3PbI3 (MAPbI3) films and planar heterojunction devices under proton irradiation up to 1 × 1016 p cm−2 were studied. 5% of Cs+ doping can increase the cohesive energy of MAPbI3 and effectively alleviate the lattice strain induced by proton irradiation, thereby enhancing the crystallinity and stability of films. The bandgap changes of irradiated Cs0.05MA0.95PbI3 films under the identical fluence were only one third of that of MAPbI3 films. Upon irradiation under the fluence of 1 × 1014 p cm−2, the density of trap states in the undoped and 5%Cs-doped films increased by 71% and 9%, respectively, and the average PCE of 20 corresponding devices decreased only by 12% and 9%, respectively. This proves that the replacement of organic methylamine ion with inorganic cesium ion contributes to the improvement of MAPbI3 resistance to proton irradiation, thus confirming the application prospects of mixed-cation or all-inorganic perovskite solar cells in spacecraft.

The degradation and recovery behavior of mixed-cation perovskite solar cells in moisture and a gas mixture environment

Perovskite solar cell stability was investigated in moisture and gas mixtures. Moisture accelerates the degradation rate, but once light is removed, the performance is recoverable.

The Effect of Cs/FA Ratio on the Long‐Term Stability of Mixed Cation Perovskite Solar Cells

Perovskite Solar Cells In article number 2100660, Do-Hyung Kim, Han-Ki Kim, and co-workers found that the excel-lent long-term stability originates from the appropriate tolerance factor and low thermody-namic decomposition energy, which underpins the strong potential for the commercializa-tion of Cs-containing mixed FAPbI3 perovskite solar cells.

The Effect of Cs/FA Ratio on the Long‐Term Stability of Mixed Cation Perovskite Solar Cells

Formamidinium lead iodide (FAPbI3) is ideal for highly efficient and operationally stable perovskite solar cells (PSC). However, a primary challenge for FAPbI3 PSC is to suppress the phase transition from the photoactive black phase into the yellow nonperovskite δ‐phase. The preparation of Cs‐containing mixed FAPbI3 perovskite by cation stoichiometric engineering is demonstrated and the influence of the Cs/FA ratio on its phase stability and device performance is discussed. By exploring the optimal ratio of Cs and FA cations in Cs x FA1−x Pb(I0.94Br0.06)3 perovskite, an inverted planar device with Cs0.17FA0.83Pb(I0.94Br0.06)3 composition shows the best power conversion efficiency (PCE) of 16.5% in an active area of 1.08 cm2. More importantly, the Cs0.17FA0.83Pb(I0.94Br0.06)3 perovskite photoactive layer showed remarkable long‐term stability, maintaining 88.1% of its initial efficiency for 1128 h in the presence of moisture and oxygen and without any encapsulation. The excellent long‐term stability is found to originate from the appropriate tolerance factor and low thermodynamic decomposition energy, which underpins the strong potential for the commercialization of Cs‐containing mixed FAPbI3 PSCs.

Effects of HTL/ETL properties on the performance of (FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cells

Mixed cation perovskite solar cells (PSCs) have shown high stability over 1000 h under outdoor conditions. In this paper, we simulated fluorine-doped tin oxide/TiO2/(FAPbI3)0.85(MAPbBr3)0.15/ Spiro-OMeTAD solar cell as the base structure by SCAPS-1D software. We then studied the effects of E V position of hole transport layer (HTL) and E C position of electron transport layer (ETL) and carrier density of HTL and ETL, on the performance of the solar cells. Simulation results showed that the carrier density of HTL and ETL has outstanding effect on the performance of the mixed cation PSC through band alignment between the layers. Moreover, we studied the influence of defect density of ETL/perovskite and perovskite/HTL interface layers. According to simulation results, we predict that using Spiro-OMeTAD as HTL and Nb-doped TiO2 as ETL, that have shown capability of fabrication with PSCs, improves the power conversion efficiency to 19.75%.

Synergistic Defect Passivation for Highly Efficient and Stable Perovskite Solar Cells Using Sodium Dodecyl Benzene Sulfonate

Polycrystalline perovskite films with a lot of ionic defects and pinholes are the key factors to both the efficiency and stability of organic–inorganic halide perovskite devices. Here, an efficient additive modification process is reported for passivating defects in the perovskite film with sodium dodecyl benzene sulfonate (SDBS), leading to valid defect passivation of perovskite films and conspicuous improvement in both power conversion efficiency (PCE) and stability of mixed-cation perovskite solar cells (PSCs). Upon incorporating SDBS in perovskite precursor, the PCE of planar structure mixed-cation PSCs shows a best PCE of 20.88% with negligible hysteresis behavior (1.27), which are outstanding and better than that of the control PSCs (PCE = 19.15% and H-index = 8.18). The benzene sulfonic acid group of SDBS attracts lead ions of the perovskite and attaches on the surfaces of the perovskite crystal, which obviously slows down the process of perovskite crystallization and benefits from the high-quality film with lower defect density preparation. Also, the long-chain alkyl groups of SDBS with hydrophobicity benefit from the perovskite film with better water stability. In addition, SDBS modification decreases the electron trap density, improving charge utilization, suppressing charge recombination, and resulting in an increase of the efficiency of the mixed-cation PSC devices. Moreover, PSCs with optimal SDBS passivation show a better ambient stability compared with the control PSCs. These results indicate that the synergistic interfacial passivation of SDBS in perovskites is beneficial in fabricating highly efficient and air stable PSCs.