Copper-copper iodide hybrid nanostructure as hole transport material for efficient and stable inverted perovskite solar cells

A CuI coated Cu hybrid nanostructure by partial iodation of Cu nanowires was used as hole transport material(HTM) to enhance the charge transfer in inverted perovskite solar cells(PSCs). The outer CuI achieved efficient charge extraction, and the inner copper facilitated the extracted charges to be rapidly transferred, further improving the overall cell performance. Furthermore,we employed a mixture of [6,6]-phenyl-C71-butyric acid methyl ester(PCBM) and ZnO nanoparticles as electron transport material(ETM) to achieve the fabrication of stable PSCs. The best efficiency was up to 18.8%. This work represents a fundamental clue for the design of efficient and stable PSCs using the chemical in-situ construction strategy for HTM and integration of PCBM and ZnO as ETM.     

Reformation of thiophene-functionalized phthalocyanine isomers for defect passivation to achieve stable and efficient perovskite solar cells

Lewis acid–base passivation is a significant technique to achieve structural stability of perovskite solar cells(PSCs) by overcoming the issues of wide grain boundaries, crystal defects, and the instability of PSCs. In this work, the combined effects of thiophene with phthalocyanine(Pc) as isomers(S2 and S3)on the photovoltaic performance of PSCs were studied for the first time. Through density functional theory calculations, we confirmed that the position of the S atom in the structure affects ...     

Two-dimensional perovskite capping layer for stable and efficient tin-lead perovskite solar cells

Mixed tin-lead iodide perovskites exhibit the characteristics of low toxicity and improved light harvesting ability up to nearinfrared(NIR) spectral region, making them as an attractive alternative for traditional lead based perovskites. However, the performance of lead-based perovskites solar cells is still far inferior to their lead analogues owing to the unavoidable oxidation of Sn~(2+)to Sn~(4+). Here we introduced two-dimensional(2D) perovskite on the top of three dimensional(3D) perovskite film as a capping layer to reduce the self-oxidation, and thus improved the device stability. 2D capping layer was then confirmed by X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) analysis. The existence of the 2D protecting thin layer significantly reduce the spontaneous Sn~(2+)oxidation, thus improve the device performance and reduce the hysteresis. The phenomena could be ascribed to the improved charge extraction efficiency causing by prohibited nonradiative recombination. On top of this, the photovoltaic devices based on conventional-structure configuration were fabricated. Taking advantage of the 2D capping layer, 2D/3D hybrid perovskite photovoltaic devices achieve a open-circuit voltage(Voc) of 0.77 V with short circuit current density(Jsc) of 26.60 mA cm~(-2), delivering the best-performing power conversion efficiency of 15.5%. Moreover, the 2D/3D perovskite devices maintained 60% its initial efficiency after 40 h exposed in air(humidity around 30%, temperature 22 °C),while 3D perovskite-based devices completely failed.     

A novel phenoxazine-based hole transport material for efficient perovskite solar cell

Based on the previous research work in our laboratory, we have designed and synthesized a small-molecule,hole transport material(HTM) POZ6-2 using phenoxazine(POZ) as central unit and dicyanovinyl units as electron-withdrawing terminal groups. Through the introduction of a 2-ethyl-hexyl bulky chain into the POZ core unit, POZ6-2 exhibits good solubility in organic solvents. In addition, POZ6-2 possesses appropriate energy levels in combination with a high hole mobility and conductivity in its pristine form. Therefore, it can readily be used as a dopant-free HTM in perovskite solar cells(PSCs) and a conversion efficiency of 10.3% was obtained. The conductivity of the POZ6-2 layer can be markedly enhanced via doping in combination with typical additives, such as 4-tert-butylpyridine(TBP) and lithium bis(trifluoromethanesulfonyl) imide(Li TFSI).Correspondingly, the efficiency of the PSCs was further improved to 12.3% using doping strategies. Under the same conditions, reference devices based on the well-known HTM Spiro-OMe TAD show an efficiency of 12.8%.     

Simultaneous passivation of bulk and interface defects through synergistic effect of anion and cation toward efficient and stable planar perovskite solar cells

Bulk and interface carrier nonradiative recombination losses impede the further improvement of power conversion efficiency (PCE) and stability of perovskite sol...     

Pyridine-triphenylamine hole transport material for inverted perovskite solar cells

In the light of superior interaction between pyridine unit and perovskite,a facile star-shaped triphenylamine-based hole transport material(HTM)incorporating pyridine core(coded as H-Pyr)is designed and synthesized.A reference HTM with benzene core,coded as H-Ben,is also prepared for a comparative study.The effects of varying core on HTMs are investigated by comparing the photophysical,electrochemical and hole mobility properties.It is found that pyridine core exhibits better conjunction and decreased dihedral angles with triphenylamine side arms than that of benzene,leading to obviously better hole mobility and well-matched work function.The perovskite film prepared on H-Pyr also shows improved crystallization than on H-Ben.Photoluminescence and electrochemical impedance studies indicate improved charge extraction and reduced recombination in the H-Pyr-based perovskite solar cells.Consequently,H-Pyr-based device exhibits higher efficiency than H-Ben-based one.After doping with a Lewis acid,tris(pentafluorophenyl)borane,H-Pyr-based device delivers a champion efficiency of 17.09%,which is much higher compared with 12.14% of the device employing conventional poly(3,4-ethy lenedioxythiophene)polystyrene sulfonate(PEDOT:PSS)as HTM.Moreover,the H-Pyr-based device displays good long-term stability that the power conversion efficiency remains over 80% of the initial value after storage in ambient(relative humidity=50±5%)for 20 days.     

Inorganic p-type semiconductors and carbon materials based hole transport materials for perovskite solar cells

Incorporation of proper inorganic p-type semiconductors as hole transport layer has great potential to increase long-term stability while maintaining high power conversion efficiency of perovskite solar cells with low material cost.     

Nano-capillary induced assemble of quantum dots on perovskite grain boundaries for efficient and stable perovskite solar cells

In recent years, perovskite solar cells(PSCs) have propelled into the limelight owing to rapid development of efficiency; however, the abundant defects at the perovskite grain boundaries result in unwanted energy loss and structural degradation. Here, the grain boundaries of perovskite polycrystalline films have been found to act as nanocapillaries for capturing perovskite quantum dots(PQDs), which enable the conformal assemble of PQDs at the top interspace between perovskite grains. The existen...     

Materials and structures for the electron transport layer of efficient and stable perovskite solar cells

The electron transport layer plays a vital function in extracting and transporting photogenerated electrons, modifying the interface, aligning the interfacial energy level and minimizing the charge recombination in perovskite solar cells. This review summarizes the recent research progress on electron transport materials of metal oxides, organic molecules and multilayers. The doped metal oxides as electron transport materials in regular perovskite solar cells show improved device performance relative to their non-doped counterpart due to enhanced electron mobility and energy level alignment. The non-fullerene organic electron transport materials with better electron mobility and tunable energy level alignment need to be further designed and developed despite their advantages of mechanical flexibility and wide range tunability. The multilayer electron transport materials are suggested to be an important direction of research for efficient and stable perovskite solar cells because of their favorable synergistic interaction.     

Surface passivation using pyridinium iodide for highly efficient planar perovskite solar cells

Perovskite solar cells have developed rapidly in the past decades.However,there are large amounts of ionic defects at the surface and grain boundaries of perovskte films which are detrimental to both the efficiency and stability of perovskite solar cells.Here,an organic halide salt pyridinium iodide(PyI) is used in cation-anion-mixed perovskite for surface defect passivation.Different from the treatment with Lewis base pyridine(Py) which can only bind to the under-coordinated Pb ions,zwitterion molecule PyI can not only fill negative charged iodine vacancies,but also interact with positive charged defects.Compared with Py treatment,PyI treatment results in smoother surface,less defect densities and nonradiative recombination in perovskite,leading to an improved VOC, negligible J-V hysteresis and stable performance of devices.As a result,the champion PyI-treated planar perovskite solar cell with a high VOC of 1.187 V achieves an efficiency of 21.42%,which is higher than 20.37% of Py-treated device,while the pristine device without any treatment gets an efficiency of 18.83% at the same experiment conditions.     

Cross-linked hole transport layers for high-efficiency perovskite tandem solar cells

Science China Chemistry - Perovskite tandem solar cells have recently received extensive attention due to their promise of achieving power conversion efficiency (PCE) beyond the limits of...     

Large area,waterproof, air stable and cost effective efficient perovskite solar cells through modified carbon hole extraction layer

The conventional unstable and expensive hole transporting materials (HTM) has been replaced by cost effective modified carbon hole extraction layer. Herein, we demonstrated a new recipe toward air stable and waterproof modified carbon hole extraction layer for efficient perovskite solar cells (PSCs). The commercial available carbon ink modified with methylammonium lead iodide (MAI) has been used as hole extraction layer for ambipolar perovskite solar cells. The fabricated optimized perovskite solar cell having Glass/FTO/mp-TiO₂/MAPbI_3-xCl_x/carbon + MAI/Carbon configuration exhibited η = 13.87% power conversion efficiency (PCE) with open circuit voltage (V_OC) 0.997 V, current density (J_SC) = 21.41 mAcm^?2 and fill factor (FF) 0.65. Furthermore, the air stability were tested at room temperature in open atmosphere. The water proof stability was tested under water flushing. Our results revealed that, although our carbon based devices show lower PCE (η = 13.87%) compared to spiro-MeOTAD HTM (η = 15%), the fabricated PSCs could even retain >90% after water exposure >20 times and ambient air stability more than 160 days. Further the large area device (>1 cm²) device shows 13.04% PCE with Jsc = 21.47 mAcm^?2, V_OC = 0.996 V and FF = 0.61. We have also demonstrated >13% efficiency for large area device (>1.1 cm²), demonstrating that the developed method is simple, cost effective and promising towards large area device fabrication. The developed methodology based on low cost carbon hole extraction layer will be helpful towards waterproof and air stable perovskite solar cells for large-area devices.     

Multifunctional dopamine-assisted preparation of efficient and stable perovskite solar cells

Perovskite solar cells(PSCs)show great potential for next-generation photovoltaics,due to their excellent optical and electrical properties.However,defects existing inside the perovskite film impair both the performance and stability of the device.Uncoordinated Pb²⁺,uncoordinated I^-,and metallic Pb(Pb⁰)are the main defects occur during perovskite film preparation and device operation,due to the volatilization of organic cationic components.Passivating these defects is a desirable tas k,because they are non-radiative recombination centers that cause open-circuit voltage(VOC)loss and degradation of the perovskite layer.Herein,the multifunctional bioactive compound dopamine(DA)is introduced for the first time to control the perovskite film formation and passivate the uncoordinated Pb²⁺defects via Lewis acid-base interactions.The Pb⁰ and I^-defects are effectively suppressed by the DA treatment.At the same time,the DA treatment results in a stronger crystal orientation along the(110)plane and upshifts the valence band of perovskite closer to the highest occupied molecular orbital(HOMO)of the hole transport layer(2,2’,7,7’-tetrakis(N,N’-di-pmethoxyphenylamine)-9,9’-spirobifluorene,spiro-OMeTAD),which is beneficial for charge separation and transport processes.Consequently,the stability of MAPbI₃(MA=CH₃NH₃)PSCs prepared with the DA additive(especially the thermal stability)is effectively improved due to the better crystallinity and lower number of defect trap states of the perovskite film.The optimized MAPbI3 PSCs maintain approximately 90% of their original power conversion efficiency(PCE)upon annealing at 85℃ for 120 h.The best performance triple-cation perovskite(Cs_0.05(FA_0.83MA_0.17)_0.95Pb(I_0.83Br_0.17)₃)(FA=formamidinium)solar cell with ITO/SnO₂/Cs_0.05(FA_0.83MA_0.17)_0.95Pb(I_0.83Br_0.17)₃:DA/spiro-OMeTAD/MoO₃/Ag(ITO=indium tin oxide)structure shows a PCE of 21.03% with negligible hysteresis,which is dramatically enhanced compared to that of the control device(18.31%).Therefore,this work presents a simple and effective way to improve the efficiency and stability of PSCs by DA treatment.     

Unraveling abnormal buried interface anion defect passivation mechanisms depending on cation-induced steric hindrance for efficient and stable perovskite solar cells

Although ionic liquids (ILs) have been widely employed to heal the defects in perovskite solar cells (PSCs),the corresponding defect passivation mechanisms are not thoroughly understood up to now.Herein,we first reveal an abnormal buried interface anion defect passivation mechanism depending on cationinduced steric hindrance.The IL molecules containing the same anion ([BF₄]^-) and different sizes of imidazolium cations induced by substituent size are used to manipulate burie...     

Vapor treatment enables efficient and stable FAPbI_3 perovskite solar cells

Metal halide perovskite solar cells(PSCs)have attracted extensive research interest in recent years due to their lowcost processing,high power conversion efficiency(PCE),and tunable bandgap enabling tandem photovoltaics(PVs).Over the past decade,PSCs have witnessed an impressive increase in PCEs from 3.8%to 25.5%,which is the highest among thin-film PV technologies and is comparable to those of crystalline silicon solar cells[1].     

4-Tert-butylpyridine-assisted low-cost and soluble copper phthalocyanine as dopant-free hole transport layer for efficient Pb- and Sn-based perovskite solar cells

The preparation of suitable hole transport material(HTM) is critical to the performance and stability of perovskite solar cells(PSCs) with low-cost. Herein, a mass producible and soluble copper phthalocyanine decorated with butoxy donor groups(CuPcOBu) was designed as HTM and prepared by a facile two-step synthetic route. To generate high quality HTM film, 4-tertbutylpyridine(tBP) was doped into CuPc-OBu to prepare the film and then removed by annealing. Such a t BP-assisted strategy resulted in the best efficiency of the PSCs with lead trihalide perovskite up to 19.0%(small-area of 0.1 cm~2) and 10.1%(the active area of 8.0 cm~2 for the module device). And the best efficiency of the tin-based PSCs with CuPc-OBu reached to 6.9%.More importantly, the device with CuPc-OBu as HTM revealed the remarkably enhanced stability. This work provides a new strategy to improve the film-quality of free-doping HTMs and enhance the efficiency and stability of Pb-and Sn-based PSCs with low-cost.     

Molecular ferroelectrics for efficient perovskite solar cells

During the past decade,the power conversion efficiencies(PCEs)of organic-inorganic hybrid perovskite solar cells(PSCs)have exceeded 25%[1],which is expected to be one of the candidates for the next generation of thin-film photovoltaic technology.Fundamentally speaking,the performance of PSCs mainly depends on the light absorption capacity,defect passivation and photo-induced exciton separation and extraction of perovskite films.Under the light illumination,photo-induced excitons were separated and extracted by the built-in electric field of PSCs.     

Intermediates transformation for efficient perovskite solar cells

Perovskite materials have made a great progress in terms of the power conversion efficiency(PCE), rising from 3.8% to 25.2%. To obtain pinhole-free, superior crystal, and high-quality perovskite films with less defect, intermediates transformation is important, which has been clearly studied and widely applied.In this review, we systematically summarize the commonly formed intermediates and detailedly analyze their mechanisms from five aspects:(1) Solvent-induced intermediate;(2) HI-induced intermediate;(3)CH3NH2-induced intermediate;(4) MAAc-induced intermediate;(5) other intermediates. Finally, we also provide some prospects on high-quality perovskite fabrication based on using intermediates prudently.     

Biopolymer passivation for high-performance perovskite solar cells by blade coating

Thin films of perovskite deposited from solution inevitably introduce large number of defects,which serve as recombination centers and are detrimental for solar cell performance.Although many small molecules and polymers have been delicately designed to migrate defects of perovskite films,exploiting credible passivation agents based on natural materials would offer an alternative approach.Here,an ecofriendly and cost-effective biomaterial,ploy-L-lysine(PLL),is identified to effectively passivate the defects of perovskite films prepared by blade-coating.It is found that incorporation of a small amount(2.5 mg mL^-1)of PLL significantly boosts the performance of printed devices,yielding a high efficiency of 19.45% with an increase in open-circuit voltage by up to 100 mV.Density functional theory calculations combined with X-ray photoelectron spectroscopy reveal that the functional groups(-NH2,-COOH)of PLL effectively migrate the Pb-I antisite defects via Pb-N coordination and suppress the formation of metallic Pb in the blade-coated perovskite film.This work suggests a viable avenue to exploit passivation agents from natural materials for preparation of high-quality perovskite layers for optoelectronic applications.     

Additive engineering for stable halide perovskite solar cells

Halide perovskite solar cells(PSCs)have already demonstrated power conversion efficiencies above 25％,which makes them one of the most attractive photovoltaic te...