A review on two-dimensional (2D) and 2D-3D multidimensional perovskite solar cells: Perovskites structures,stability, and photovoltaic performances

Perovskite solar cells (PSCs) fabricated with two-dimensional (2D) halide and 2D-3D mixed-halide materials are remarkable for their optoelectronic properties. The 2D perovskite structures are extremely stable but show limited charge transport and large bandgap for solar cell applications. To overcome these challenges, multidimensional 2D-3D perovskite materials are used to maintain simultaneously, a long-term stability, and high performance. In this review, we discuss the recent progress and the advantages of 2D and 2D-3D perovskite materials as absorber for solar cell applications. First, we discuss the structure and the unique properties of 2D and multidimensional 2D-3D perovskites materials. Second, the stability of 2D and 2D-3D mixed perovskites and the perspects of PSCs are hashed out.     

Enhanced efficiency and stability of perovskite solar cells by 2D perovskite vapor-assisted interface optimization

Organic–inorganic perovskites solar cells(PSCs)have attracted great attention due to their rapid progress in power conversion efficiency(PCE).However,there is still an enormous challenge to achieve both high efficiency and stability devices as the decomposition of perovskite materials under humid and light conditions.Herein,we demonstrate that high efficiency and stability of PSCs can be obtained by the reaction of three-dimensional(3D)perovskite with 1,4-butanediamine iodide(BEAI2)vapor.The incorporation of BEAI2 intensively promotes the crystallization of perovskite film with large grain size(~500 nm).Further characterization reveals that the post-treatment perovskite film delivered low interface trap density with long carrier lifetime(>200 ns),long carrier diffusion length(>600 nm)and large carrier mobility(>1.5 cm^2 V-1S-1).Solar cells employing such post-treatment films demonstrated 19.58%PCE without hysteresis.Moreover,the post-treatment devices can retain over 90%original efficiencies stored under ambient atmospheric conditions and exhibit better stability under 85℃and continuous illumination as a two-dimensional(2D)perovskite thin layer is formed on the surface/or at the grain boundaries of 3D perovskite.This study offers an effective way to obtain PSCs with high efficiency and stability.     

Beyond two-dimension: One-and zero-dimensional halide perovskites as new-generation passivators for high-performance perovskite solar cells

Perovskite solar cells(PSCs) as a rising star in the photovoltaic field have received rapidly increasing attention recently due to the boosting power conversion efficiencies(PCEs) from 3.8% to 25.7% in the last13 years. Nevertheless, the conventional PSCs with three-dimensional(3D) halide perovskites as light absorbers suffer from inferior PCEs and poor durability under sunlight, high-temperature and humid conditions due to the high defect amount and structural instability of 3D perovskites, res...     

Defect mitigation using d-penicillamine for efficient methylammonium-free perovskite solar cells with high operational stability

Trap-dominated non-radiative charge recombination is one of the key factors that limit the performance of perovskite solar cells (PSCs), which was widely studied in methylammonium (MA) containing PSCs. However, there is a need to elucidate the defect chemistry of thermally stable, MA-free, cesium/formamidinium (Cs/FA)-based perovskites. Herein, we show that d-penicillamine (PA), an edible antidote for treating heavy metal ions, not only effectively passivates the iodine vacancies (Pb²⁺ defects) through coordination with the –SH and –COOH groups in PA, but also finely tunes the crystallinity of Cs/FA-based perovskite film. Benefiting from these merits, a reduction of non-radiative recombination and an increase in photoluminescence lifetime have been achieved. As a result, the champion MA-free device exhibits an impressive power conversion efficiency (PCE) of 22.4%, an open-circuit voltage of 1.163 V, a notable fill factor of 82%, and excellent long-term operational stability. Moreover, the defect passivation strategy can be further extended to a mini module (substrate: 4 × 4 cm², active area: 7.2 cm²) as well as a wide-bandgap (∼1.73 eV) Cs/FA perovskite system by delivering PCEs of 16.3% and 20.2%, respectively, demonstrating its universality in defect passivation for efficient PSCs.

Iodine vacancy defects in MA-free perovskite are effectively passivated through the interaction between Pb²⁺ and the functional groups in d-penicillamine, resulting in an impressive efficiency of 22.4% along with excellent operational stability.     

Heat diffusion optimization in high performance perovskite solar cells integrated with zeolite

Heat accumulation inside perovskite solar cells causes the decomposition of the perovskite layer and hole transport materials(HTMs) under working conditions,yielding a decrease in long-term stability.Here,we present a zeolite-assisted heat conduction strategy by introducing economic zeolite crystals(e.g.,NaX,NaY,and ZSM-5) as a cooling filter to induce heat diffusion.The fitted thermal diffusion kinetic equation from real-time infrared thermal imaging technology reveals the zeolite skeleton assi...     

Supersaturation controlled growth of MAFAPbI_3 perovskite film for high efficiency solar cells

Controlling the nucleation and growth of organic-inorganic hybrids perovskite is of key importance to improve the morphology and crystallinity of perovskite films. However, the growth mechanism of perovskite films based on classical crystallization theory is not fully understood. Here, we develop a supersaturation controlled strategy(SCS) to balance the nucleation and crystal growth speeds. By this strategy, we are able to find an ideal supersaturation region to realize a balance of nucleation and crystal growth, which yields highly crystallized perovskite films with micrometer-scale grains. Besides, we provide a thoughtful analysis of nucleation and growth based on the fabrication of the perovskite films. As a result, the highest photovoltaic power conversion efficiencies(PCE) of 19.70% and 20.31% are obtained for the planar and the meso-superstructured devices, respectively. This strategy sheds some light for understanding the film growth mechanism of high quality perovskite film, and it provides a facile strategy to fabricate high efficiency perovskite solar cells.     

Effect of hole-transporting materials on the photovoltaic performance and stability of all-ambient-processed perovskite solar cells

High-efficiency perovskite solar cells(PSCs) reported hitherto have been mostly prepared in a moisture and oxygen-free glove-box atmosphere, which hampers upscaling and real-time performance assessment of this exciting photovoltaic technology. In this work, we have systematically studied the feasibility of allambient-processing of PSCs and evaluated their photovoltaic performance. It has been shown that phasepure crystalline tetragonal MAPbI_3 perovskite films are instantly formed in ambient air at room temperature by a two-step spin coating process, undermining the need for dry atmosphere and post-annealing.All-ambient-processed PSCs with a configuration of FTO/TiO_2/MAPbI_3/Spiro-OMeTAD/Au achieve opencircuit voltage(990 mV) and short-circuit current density(20.31 mA/cm~2) comparable to those of best reported glove-box processed devices. Nevertheless, device power conversion efficiency is still constrained at 5% by the unusually low fill-factor of 0.25. Dark current–voltage characteristics reveal poor conductivity of hole-transporting layer caused by lack of oxidized spiro-OMe TAD species, resulting in high seriesresistance and decreased fill-factor. The study also establishes that the above limitations can be readily overcome by employing an inorganic p-type semiconductor, copper thiocyanate, as ambient-processable hole-transporting layer to yield a fill-factor of 0.54 and a power conversion efficiency of 7.19%. The present findings can have important implications in industrially viable fabrication of large-area PSCs.     

Graded interface engineering of 3D/2D halide perovskite solar cells through ultrathin(PEA)_2PbI_4 nanosheets

2D halide perovskites have emerged as promising materials because of their stability and passivation effect in perovskite solar cells(PSCs).However,the introduction of bulky organic ammonium cations from 2D halide perovskites would decrease the device performance generally compared to the traditional 3D MAPbI_3.Incorporation of ultrathin 2D halide perovskite nanosheets(NSs) with 3D MAPbI_3 could address this issue.Herein,we re port a rationally designed PSCs with dimensional graded 3D/2D MAPbI_3/(PEA)2 PbI_4 heterojunction,in which 2D(PEA)2 PbI_4 NSs were synthesized and incorporated between 3D MAPbI_3 and hole-transporting layer.Besides the significantly improved stability,a notable increasement in power conversion efficiency(PCE) of 20% was obtained for the 3D/2D perovskite solar cells due to the favourable band alignment among(PEA)_2 PbI_4 NSs and the other components.The graded structure of MAPbI_3/(PEA)2 PbI_4 would upshift the energy level continuously,which enhances the hole extraction efficiency thus reduces the interface charge recombination,leading to the increasements of VOC from1.04 V to 1.07 V,Jsc from 21.81 mA/cm~2 to 23.15 mA/cm~2 and the fill factor from 67.89% to 74.78%,and therefore an overall PCE of 18.53%.     

Development of formamidinium lead iodide-based perovskite solar cells: efficiency and stability

Perovskite materials have been particularly eye-catching by virtue of their excellent properties such as high light absorption coefficient, long carrier lifetime, low exciton binding energy and ambipolar transmission (perovskites have the characteristics of transporting both electrons and holes). Limited by the wider band gap (1.55 eV), worse thermal stability and more defect states, the first widely used methylammonium lead iodide has been gradually replaced by formamidinium lead iodide (FAPbI₃) with a narrower band gap of 1.48 eV and better thermal stability. However, FAPbI₃ is stabilized as the yellow non-perovskite active phase at low temperatures, and the required black phase (α-FAPbI₃) can only be obtained at high temperatures. In this perspective, we summarize the current efforts to stabilize α-FAPbI₃, and propose that pure α-FAPbI₃ is an ideal material for single-junction cells, and a triple-layer mesoporous architecture could help to stabilize pure α-FAPbI₃. Furthermore, reducing the band gap and using tandem solar cells may ulteriorly approach the Shockley–Queisser limit efficiency. We also make a prospect that the enhancement of industrial applications as well as the lifetime of devices may help achieve commercialization of PSCs in the future.

This perspective is focused on the current development state and the future development direction of FA-based perovskite materials and solar cells.     

Improved interfacial property by small molecule ethanediamine for high performance inverted planar perovskite solar cells

We report a simple and effective method to realize desirable interfacial property for inverted planar perovskite solar cells(PSCs)by using small molecule ethanediamine for the construction of a novel polyelectrolyte hole transport material(P3CT-ED HTM).It is found that P3CT-ED can not only improve the hole transport property of P3CT-K but also improve the crystallinity of adjacent perovskite film.In addition,the introduction of ethanediamine into P3CT realigns the conduction and valence bands upwards,passivates surface defects and reduces nonradiative recombination.As a consequence,compared to P3CT-K hole transport layer(HTL)based devices,the average power conversion efficiency(PCE)is boosted from17.2% to 19.6% for the counterparts with P3CT-ED,with simultaneous enhancement in open circuit voltage and fill factor.The resultant device displays a champion PCE of 20.5% with negligible hysteresis.     

Boosting efficiency and stability of 2D alternating cation perovskite solar cells via rational surface-modification: Marked passivation efficacy of anion

Two-dimensional(2D) alternating cation(ACI) perovskite surface defects,especially dominant iodine vacancies(V_Ⅰ) and undercoordinated Pb²⁺,limit the performance of perovskite solar cells(PVSCs).To address the issue,1-butyl-3-methylimidazolium trifluoro-methane-sulfonate(BMIMOTF) and its iodide counterpart(BMIMI) are utilized to modify the perovskite surface respectively.We find that BMIMI can change the perovskite surface,whereas BMIMOTF shows a nondestructive and more effec...     

Realizing high photovoltage for inverted planar heterojunction perovskite solar cells

<正>Inverted planar heterojunction perovskite solar cells (peroSCs) have caused tremendous attention due to their promise features of easy fabrication and compatibility with flexible substrates [1]. However, their power conversion efficiencies(PCE) are greatly limited by its relatively low open-circuit voltage (Voc), which is attributed to high nonradiative recombination losses owing to the existence of high density of     

A universal tactic of using Lewis-base polymer-CNTs composites as additives for high performance cm~2-sized and flexible perovskite solar cells

Lewis-base polymers have been widely utilized as additives to act as a template for the perovskite nucleation/crystal growth and passivate the under-coordinated Pb2+ sites.However,it is uncovered in this work that the polymer on the perovskite grain boundaries would significantly hinder the charge transport due to its low conductivity,which brings about free carrier recombination and photocurrent losses.To circumvent this issue while fully exploiting the benefits of polymers in passivating the trap states in perovskite,we incorporate highly conductive multiwall carbon nanotubes(CNTs) with Lewis-base polymers as coadditives in the perovskite film.Functionalizing the CNTs with-COOH group enables a selective hole-extraction and charge transport from perovskite to the hole transporting materials(HTM).By studying the charge transporting and recombination dynamics,we revealed the individual role of the polymer and CNTs in passivating the trap states and facilitating the charge transport,respectively.As a result,the perovskite solar cells(PSCs) with polymer-CNTs composites exhibit an impressive PCE of 21.7% for a small-area device(0.16 cm2) and 20.7% for a large-area device(1.0 cm2).Moreover,due to the superior mechanical flexibility of both polymer and CNTs,the polymer-CNTs composites incorporation in the perovskite film encourages the fabrication of flexible PSCs(f-PSCs) with an impressive PCE of 18.3%,and a strong mechanical durability by retaining 80%of the initial PCE after 1,000 times bending.In addition,we proved that the selection criteria of the polymers can be extended to other long-chain Lewis-base polymers,which opens new possibilities in design and synthesis of inexpensive material for this tactic towards the fabrication of high performance large-area PSCs and f-PSCs.     

Compressibility of CaZrO3 perovskite: Comparison with Ca-oxide perovskites

The evolution of the unit-cell parameters of CaZrO₃ perovskite, an orthorhombic perovskite belonging to space group Pbnm, have been determined to a pressure of 8.7 GPa at room temperature using single-crystal X-ray diffraction measurements. A fit of a third-order Birch-Murnaghan equation of state to the pressure-volume data yields values of V₀=258.04(2) Å³, K_T0=154(1) GPa and K₀′=5.9(3). Although CaZrO₃ perovskite does not exhibit any phase transitions in this pressure range, the compression of the structure is anisotropic with [010] approximately 20% less compressible than either [100] or [001]. Compressional moduli for the unit cell parameters are: K_a0=142(1) GPa and K_a0′=4.4(2), K_b0=177(2) GPa and K_b0′=9.4(5), K_c0=146(2) GPa and K_c0′=5.4(4). Comparison with other orthorhombic Ca-oxide perovskites shows that there is systematic increase in compressional anisotropy with increasing distortion from cubic symmetry.     

Minimizing interfacial energy losses in inverted perovskite solar cells by a dipolar stereochemical 2D perovskite interface

Inverted perovskite solar cells(PSCs) have attracted broad research and industrial interest owing to their suppressed hysteresis,cost-effectiveness,and easy-fabrication.However,the issue of non-radiative recombination losses at the n-type interface between the perovskite and fullerene has impeded further improvement of photovoltaic performance.Here,we modify the n-type interface of FAPbI₃ perovskite films by constructing a stereochemical two-dimensional(2D) perovskite interlayer,in wh...     

I2界面修饰对全无机CsPbBr3钙钛矿太阳能电池性能的影响

通过在 CsPbBr₃薄膜上旋涂一次 I₂的异丙醇溶液以修饰 CsPbBr₃吸光层,钝化 CsPbBr₃层表面缺陷,改善 CsPbBr₃薄膜形貌。同时通过利用环境友好的绿色溶剂水溶解 CsBr,显著提高了其溶解度,减少了旋涂次数,简化了电池制备流程。实验结果表明,在CsPbBr₃钙钛矿太阳能电池(perovskite solar cells,PSCs)中,使用5 mg·mL^-1 I₂的异丙醇溶液界面修饰的器件具有最佳光伏性能,其最高开路电压(open-circuit voltage,V_OC)为1.55 V,短路电流密度(short circuit current density,J_SC)为7.45 mA·cm^-2,填充因子(fill factor,FF)为85.54%,光电转换效率(photoelectric conversion efficiency,PCE)达到了9.88%。     

I2界面修饰对全无机CsPbBr3钙钛矿太阳能电池性能的影响

通过在 CsPbBr₃薄膜上旋涂一次 I₂的异丙醇溶液以修饰 CsPbBr₃吸光层,钝化 CsPbBr₃层表面缺陷,改善 CsPbBr₃薄膜形貌。同时通过利用环境友好的绿色溶剂水溶解 CsBr,显著提高了其溶解度,减少了旋涂次数,简化了电池制备流程。实验结果表明,在CsPbBr₃钙钛矿太阳能电池(perovskite solar cells,PSCs)中,使用5 mg·mL^-1 I₂的异丙醇溶液界面修饰的器件具有最佳光伏性能,其最高开路电压(open-circuit voltage,V_OC)为1.55 V,短路电流密度(short circuit current density,J_SC)为7.45 mA·cm^-2,填充因子(fill factor,FF)为85.54%,光电转换效率(photoelectric conversion efficiency,PCE)达到了9.88%。     

Tuning crystal orientation and charge transport of quasi-2D perovskites via halogen-substituted benzylammonium for efficient solar cells

Quasi-two-dimensional(quasi-2D) perovskites with high stability usually suffers from poor device efficiency. Chemical tuning of the spacer cations has been an effective strategy to achieve efficient and stable quasi-2D perovskite solar cells. Here, we demonstrate that 3-halogon-substituted benzylammonium iodide(3X-BAI, X = F, Cl, Br, I) can significantly affect the orientation of low-dimensional perovskites and charge transport from perovskite to hole extraction layer, as well as device performa...     

Review on engineering two-dimensional nanomaterials for promoting efficiency and stability of perovskite solar cells

Perovskite solar cell(PSC) has gradually shown its great superiority in photovoltaic filed to compete commercial solar cells owing to its great advantages, such as high efficiency and low fabrication cost. On the way towards commercialization, great efforts have been achieved by accelerating charge extraction and reducing carrier recombination. Recently, two-dimensional(2 D) layered materials have attracted increasing interests for application in PSCs due to their distinctive chemical and physic...     

ZnO/ZnS core-shell composites for low-temperature-processed perovskite solar cells

Electron transport layers(ETLs)in perovskite solar cells(PSCs)are a key factor to determine the photovoltaic performance.Herein,we demonstrate preparation of Zn O/ZnS core-shell composites through directly synthesizing ZnS on the ZnO nanoparticles in solution.We confirmed the formation of ZnO/ZnS core-shell composites by the uses of X-ray diffraction patterns and the Fourier transform infrared spectroscopy.ZnO/ZnS composites exhibit much homogeneous surface morphology as compared with the bare Zn O as revealed in the scanning electronic microscopy.Moreover,the upper shift of conduction band level upon composition of the Zn O/Zn S film results in a better alignment of energy level,which facilitates cascade charge extraction and thus improves the current density of perovskite solar cell.The shift of conduction band also improves the voltage of the PSCs.The photoluminescence(PL)spectroscopies measured in both steady and transient states were carried out to characterize the charge extraction at the interface between CH_3NH_3PbI_3and the electron transport layers of either ZnO or ZnO/ZnS composite.The ZnO/ZnS composite can more efficiently quench the PL signal of perovskite absorber than bare Zn O resulting in enhanced photocurrent generation in PSCs.