CsPbI2Br Perovskite Solar Cells Research Articles

Effective Surface Treatment for High-Performance Inverted CsPbI2Br Perovskite Solar Cells with Efficiency of 15.92%

HighlightsA simple and multifunctional surface treatment strategy is proposed to address the inferior-performance inverted CsPbI2Br perovskite solar cells (PSCs).The induced-ions exchange can align energy levels, passivate both GBs and surface, and gift the solid protection from external erosions.The inverted CsPbI2Br PSCs reveal a champion efficiency of 15.92% and superior stability after moisture, operational, and thermal ages.Developing high-efficiency and stable inverted CsPbI2Br perovskite solar cells is vitally urgent for their unique advantages of removing adverse dopants and compatible process with tandem cells in comparison with the regular. However, relatively low opening circuit voltage (Voc) and limited moisture stability have lagged their progress far from the regular. Here, we propose an effective surface treatment strategy with high-temperature FABr treatment to address these issues. The induced ions exchange can not only adjust energy level, but also gift effective passivation. Meanwhile, the gradient distribution of FA+ can accelerate the carriers transport to further suppress bulk recombination. Besides, the Br-rich surface and FA+ substitution can isolate moisture erosions. As a result, the optimized devices show champion efficiency of 15.92% with Voc of 1.223 V. In addition, the tolerance of humidity and operation get significant promotion: maintaining 91.7% efficiency after aged at RH 20% ambient condition for 1300 h and 81.8% via maximum power point tracking at 45 °C for 500 h in N2. Furthermore, the unpackaged devices realize the rare reported air operational stability and, respectively, remain almost efficiency (98.9%) after operated under RH 35% for 600 min and 91.2% under RH 50% for 300 min.Graphic

Dopant free mixture of Spiro-OMeTAD and PTAA with tunable wettability as hole transport layer enhancing performance of inverted CsPbI2Br perovskite solar cells

To date, doped 2,2,7,7-Tetrakis(N,N-dip-methoxyphenylamine)-9,9-spirobifluorene (Spiro-OMeTAD) is still state-of-the-art hole transport material (HTM) for inverted perovskite solar cells (PeSCs). Nevertheless, hydroscopic dopants usually lead to accelerated degradation of perovskite and hence reduce the device durability especially those based on all-inorganic perovskite. In this work, we report a series of dopant-free mixtures (SpiPA) of hydrophilic Spiro-OMeTAD and hydrophobic poly(triarylamine) (PTAA), which exhibit tunable surface wettability due to the dominant lateral phase separation. When applying them as HTM for inverted CsPbI2Br PeSCs, SpiPA-II based devices yield enhanced efficiency up to 12.52% with significantly reduced hysteresis, as compared to the devices with other mixed HTLs (SpiPA-I, SpiPA-III, SpiPA-IV) and conventional HTLs including pristine Spiro-OMeTAD (10.26%), PTAA (9.05%) and NiOx (10.75%). Additionally, the corresponding mechanism has been studied in detail.

CsPbI2Br Perovskite Solar Cells Based on Carbon Black-Containing Counter Electrodes.

CsPbI2Br perovskite solar cells (PSCs) based on carbon electrodes (CEs) are considered to be low-cost and thermally stable devices. Nevertheless, the insufficient contact and energy level mismatch between the CsPbI2Br layer and CE hinder the further enhancement of the cell efficiency. Herein, a carbon black (CB) interlayer was introduced between the perovskite layer and CE. The hole extraction was facilitated due to the larger contact area and suitable energy band alignment in the CsPbI2Br/CB interface. Further investigation indicated the diffusion of CB nanoparticles from the CE or CB layer to the CsPbI2Br film after a certain period of time. We disclosed the formation of a CB-CsPbI2Br bulk heterojunction structure due to the carbon diffusion, which resulted in an efficiency enhancement. As a result, a record efficiency of 13.13% is achieved for carbon-based inorganic PSCs. This work also reveals that the diffusion of CB nanoparticles in CB-containing PSCs is universal and inevitable, although this kind of diffusion results in the enhancement of cell efficiency.

All‐Inorganic CsPbI2Br Perovskite Solar Cell with Open‐Circuit Voltage over 1.3 V by Balancing Electron and Hole Transport

The energy loss of all‐inorganic metal halide perovskite solar cells is large, which reduces the open‐circuit voltage and photoelectron conversion efficiency of the device. Herein, it is found that the cathode electron transfer speed is much lower than the anode hole transfer speed in CsPbI2Br perovskite solar cell with fluorine‐doped tin oxide (FTO) glass/SnO2/CsPbI2Br/carbon structure, which induces charge accumulation at the cathode and energy loss of the device accordingly. By introducing a new conductive polymer additive polyaniline (PANI) to the CsPbI2Br film, the electron transfer speed at the cathode is enhanced, resulting in balanced charge transfer at both electrodes and reduced energy loss of the device. Ultraviolet photoelectron spectroscopy measurement reveals that the PANI pushes the conduction band minimum of CsPbI2Br upward, leading to stronger driving force for electron extraction. Therefore, the nonradiative recombination at the SnO2/CsPbI2Br interface is greatly suppressed. In addition, PANI can also effectively passivate defects and promote the crystal quality of CsPbI2Br, leading to reduced nonradiative recombination in perovskite materials. Accordingly, the optimized all‐inorganic CsPbI2Br solar cell delivers a high Voc of 1.33 V and power conversion efficiency (PCE) of 13.52%.

VOC Over 1.4 V for Amorphous Tin-Oxide-Based Dopant-Free CsPbI2Br Perovskite Solar Cells.

CsPbI2Br perovskite solar cells have attracted much attention because of the rapid development in their efficiency and their great potential as a top cell of tandem solar cells. However, the VOC outputs observed so far in most cases are far from that desired for a top cell. Up to now, with various kinds of treatments, the reported champion VOC is only 1.32 V, with a VOC deficit of 0.60 V. In this work, we found that aging of the SnCl2 precursor solution for the electron-transporting layer can promote the VOC of CsPbI2Br solar cells by employing a dopant-free-polymer hole transport material (HTM) over 1.40 V and efficiency over 15.5% with high reproducibility. With the champion VOC of 1.43 V, the VOC deficit was reduced to <0.50 V, which is achieved for the first time. This simple technique of SnCl2 solution aging forms a uniform and smooth amorphous SnOx film with pure Sn4+, elevates the conduction band of SnOx, and reduces the interfacial gaps and the trap state density of the device, resulting in enhancement in average VOC from ∼1.2 V in the nonaged case to ∼1.4 V in the aged case. Furthermore, the device using an aged SnCl2 solution also exhibits a much better long-term stability than that made of the fresh solution. These achievements in dopant/additive-free CsPbI2Br solar cells can be useful for future research on CsPbI2Br and tandem solar cells.

High‐Efficiency CsPbI2Br Perovskite Solar Cells with Dopant‐Free Poly(3‐hexylthiophene) Hole Transporting Layers

AbstractCsPbI2Br is emerging as a promising all‐inorganic material for perovskite solar cells (PSCs) due to its more stable lattice structure and moisture resistance compared to CsPbI3, although its device performance is still much behind this counterpart. Herein, a preannealing process is developed and systematically investigated to achieve high‐quality CsPbI2Br films by regulating the nucleation and crystallization of perovskite. The preannealing temperature and time are specifically optimized for a dopant‐free poly(3‐hexylthiophene) (P3HT)‐based device to target dopant‐induced drastic performance degradation for spiro‐OMeTAD‐based devices. The resulting P3HT‐based device exhibits comparable power conversion efficiency (PCE) to spiro‐OMeTAD‐based devices but much enhanced ambient stability with over 95% PCE after 1300 h. A diphenylamine derivative is introduced as a buffer layer to improve the energy‐level mismatch between CsPbI2Br and P3HT. A record‐high PCE of 15.50% for dopant‐free P3HT‐based CsPbI2Br PSCs is achieved by alleviating the open‐circuit voltage loss with the buffer layer. These results demonstrate that the preannealing processing together with a suitable buffer layer are applicable strategies for developing dopant‐free P3HT PSCs with high efficiency and stability.

Vacuum-Controlled Growth of CsPbI2Br for Highly Efficient and Stable All-Inorganic Perovskite Solar Cells.

A high-temperature annealing process (>250 °C) is always needed to obtain high-quality α-CsPbI2Br perovskite films, which makes it a challenge in the manufacture and application of flexible photovoltaic devices. In this work, a vacuum-controlled growth (VCG) method that can effectively control the crystallization of perovskite and provide high-quality films with larger grain size and low defect density at a lower temperature is demonstrated. Besides, a facile introduction of polyethyleneimine ethoxylated (PEIE) interlayer improves the charge extraction and suppresses the carrier recombination. Therefore, the power conversion efficiency (PCE) of an all-inorganic CsPbI2Br perovskite solar cell (PSC) reaches 12.32%. The unencapsulated PSCs with VCG treatment and PEIE modification show outstanding stabilities while retaining over 95% of the initial PCE after being stored in a N2 glovebox for 1000 h. This low-temperature crystallization method and cheap interlayer introduction can drive the development of future commercialization of all-inorganic perovskite solar cells.

A facile surface passivation method for efficient inorganic CsPbI2Br perovskite solar cells with efficiencies over 15%

Recently, perovskite solar cells (PVSCs) based on CsPbI2Br have attracted increasing attention owing to their good balance between efficiency and stability. Solution-processed CsPbI2Br perovskites usually contain various defects which need passivation for PVSCs with high-performance as well as good stability. Since the degradation of perovskite films usually begins at the grain boundaries, here we report a facile defect passivation strategy by spin-coating a KF solution on the CsPbI2Br perovskite surface. The deposited KF salt mostly locates at the grain boundaries of the perovskite surface, resulting in PVSCs with improved stability. Both steady-state and time-resolved photoluminescence results suggest that the defects of perovskite were significantly passivated by KF treatment. Consequently, the best-performance PVSC based on CsPbI2Br with KF treatment shows an enhanced power conversion efficiency (PCE) of 15.01% with a larger open circuit voltage (VOC) of 1.26 V in comparison with the pristine CsPbI2Br-based counterpart which exhibits an inferior PCE of 14.14% with a VOC of 1.18 V.

Controlled n‐Doping in Air‐Stable CsPbI2Br Perovskite Solar Cells with a Record Efficiency of 16.79%

AbstractCesium‐based inorganic perovskites, such as CsPbI2Br, are promising candidates for photovoltaic applications owing to their exceptional optoelectronic properties and outstanding thermal stability. However, the power conversion efficiency of CsPbI2Br perovskite solar cells (PSCs) is still lower than those of hybrid PSCs and inorganic CsPbI3 PSCs. In this work, passivation and n‐type doping by adding CaCl2 to CsPbI2Br is demonstrated. The crystallinity of the CsPbI2Br perovskite film is enhanced, and the trap density is suppressed after adding CaCl2. In addition, the Fermi level of the CsPbI2Br is changed by the added CaCl2 to show heavy n‐type doping. As a result, the optimized CsPbI2Br PSC shows a highest open circuit voltage of 1.32 V and a record efficiency of 16.79%. Meanwhile, high air stability is demonstrated for a CsPbI2Br PSC with 90% of the initial efficiency remaining after more than 1000 h aging in air.

A surface modifier enhances the performance of the all-inorganic CsPbI2Br perovskite solar cells with efficiencies approaching 15.

All-inorganic perovskite solar cells (PSCs) are attracting considerable attention due to their promising thermal stability, but their inferior power-conversion efficiencies (PCE) hinder their realistic application. Here, we propose an approach through surface modification based on methyl ammonium halide (MAX) for inorganic CsPbI2Br solar cells processed at a low temperature. The combined benefits of the introduced MAX modifier enable the boosting of the power conversion efficiency to 14.8% with an impressive FF of 82.2% in CsPbI2Br PSCs. Our experimental analyses coupled with optical modeling indicate that the incorporated MAX leads to an effective passivation of the surface traps originating from Pb2+ and I- ions in CsPbI2Br and simultaneously mediates the crystallization of CsPbI2Br with slightly enlarged grains and reduced numbers of structural defects and pinhole. As a result, the interfacial trap-assisted recombination is suppressed and the charge extraction is promoted. Mechanistically, we show that in the presence of MAX, the deep-level traps in the perovskites are passivated, leaving the energy of the trapping centers to become shallower. In this situation, the negative impacts of the traps on carrier transport and recombination are mitigated.

Fine modification of reactively sputtered NiOX hole transport layer for application in all-inorganic CsPbI2Br perovskite solar cells

In this study, nickel oxide (NiOX) thin films were prepared by direct current (DC) reactive magnetron sputtering. The various properties of NiOX thin films including deposition rate, morphology, electrical and optical properties as well as grain structure and chemical composition were systematically investigated. The material properties of NiOX were finely modified under the monitoring of target voltage during sputtering. NiOX thin films were applied as hole transport layers (HTLs) in all-inorganic CsPbI2Br perovskite solar cells (PSCs). The highest efficiency of 12.6% had been achieved for the optimized all-inorganic CsPbI2Br PSCs with the inverted structure of Glass/FTO/NiOX(HTL)/CsPbI2Br/ZnO@C60 (electron transport layer, ETL)/Ag. The PSC still yielded over 90% of its initial power output after 10 h operation without encapsulation.

High performance all-inorganic CsPbI2Br perovskite solar cells with low energy losses

Highly efficient all-inorganic CsPbI2Br perovskite solar cells (PSCs) are fabricated by employing a simply solution processed ZnO/SnO2 bilayer electron transport layer (ETL). High iodine content CsPbI2Br film forms on the bilayer ETL surface with regular crystal grain and full coverage, which is benefit from the well crystal matching between perovskite and SnO2. On the other hand, the lower work function of ZnO compared with SnO2 reduces the energy losses (Eloss) in devices. As a result, the all-inorganic CsPbI2Br PSCs based on ZnO/SnO2 bilayer ETL demonstrate high Voc of 1.22 V and improved power conversion efficiency (PCE) to 13.7%.

Improved open-circuit voltage and ambient stability of CsPbI2Br perovskite solar cells by incorporating CH3NH3Cl

Inorganic cesium metal halide perovskites have gained research interest as absorbers in perovskite solar cells due to their superior thermal stability. Among these, CsPbI2Br, with a narrower band gap than CsPbBr3 and a better phase stability than CsPbI3, has received tremendous interest of the researchers. However, CsPbI2Br takes adverse phase transfer easily with an exposure to the water vapor in ambient air which not only brings inconvenience for researches but also puts forward very high requirement for encapsulation. Herein, a dense and uniform film is obtained by incorporating hydrophobic CH3NH3Cl (MACl) into the precursor solution. Being attributed to a good passivation effect, the defect density is decreased from 3.12 × 1016 to 1.49 × 1016 cm−3 and the average photoluminescence lifetime is increased from 8.84 to 20.6 ns. The photovoltaic device achieves a high open-circuit voltage of 1.22 V based on optimized MACl-doped film and accordingly a higher power conversion efficiency (PCE) of 12.9% which is 21.7% higher than the pristine CsPbI2Br device with PCE of 10.6%. In addition, the ambient stability of MACl-doped device has been enhanced, which is greatly attributed to the hydrophobic properties of MACl. This work provides a clue to improve ambient stability of inorganic perovskite solar cells and inspires toward further development of this material.

A facile method to improve the stability and efficiency of CsPbI2Br perovskite solar cells prepared at low temperature

CsPbI2Br has become the focus of researchers in recent years due to its excellent thermal stability compared to the organic-inorganic hybrid perovskites. However, it requires high temperature to form cubic phase, and it is difficult to maintain the cubic phase in the high humidity ambient. By adding 30 µL levulinic acid (LA) to the CsPbI2Br precursor solution, cubic phase CsPbI2Br can be obtained by spin-coating three minutes (TMS) at room temperature (RT) instead of high temperature. Based on the TMS, highly quality cubic phase CsPbI2Br film can be obtained at 80 ℃ annealing temperature, the stability of cubic phase CsPbI2Br can be significantly improved by adding LA in the CsPbI2Br precursor solution. Based on this, CsPbI2Br cells without LA achieve 11.68% power conversion efficiency (PCE) at low temperature of 80 °C and the corresponding stabilized power output is 10.31%. Furthermore, 10 µL LA addition CsPbI2Br cells keep its 50% PCE after 10 days under 35%RH and RT. This has found a new way to improve the stability of inorganic perovskite solar cells, and increasing its potential in flexible solar cells.

Efficient all-inorganic CsPbI2Br perovskite solar cell with carbon electrode by revealing crystallization kinetics and improving crystal quality

The all-inorganic CsPbI2Br shows potential applications in perovskite solar cell owning to the reasonable band gap and superior thermal stability. However, the power conversion efficiency is rather low comparing to the organic-inorganic hybrid perovskite solar cell, which is mainly induced by the inferior crystal quality. In this paper, we investigate the crystallization kinetics of CsPbI2Br perovskite film and find that the intermediate CsBr is easily formed due to its low solubility, which affects the crystalline quality of CsPbI2Br film. Employment of over-stoichiometric lead reactant (PbI2, PbBr2) or adding other lead-containing compound (PbCl2, Pb(SCN)2) effectively suppress the production of the intermediate CsBr and result in much improved crystallinity of CsPbI2Br, with a grain size of several micrometers. Accordingly, the CsPbI2Br solar cell with carbon electrode shows a stable and high power conversion efficiency of 12.19%, comparing to 9.50% of the control cell.

Inverted All-Inorganic CsPbI2Br Perovskite Solar Cells with Promoted Efficiency and Stability by Nickel Incorporation

All-inorganic CsPbI2Br perovskite solar cell with an inverted architecture of indium-tin oxide/poly[3-(4-carboxylbutyl)thiophene]/CsPbI2Br/(6,6)-phenyl-C61-butyric acid methyl ester/C60/bathocuproi...

Delocalized molecule surface electronic modification for enhanced performance and high environmental stability of CsPbI2Br perovskite solar cells

All-inorganic perovskites have drawn tremendous attentions in view of their superb thermal stability. However, unavoidable defects near the perovskite surface seriously hampers carrier transport and easily results in ion accumulation at the interface of perovskite layer and charge transport layer. Herein, delocalized thiazole and imidazole derivatives iodide salts functionalized on perovskite surface have been investigated comprehensively. These two salts post-treatment on perovskite could efficiently passivate traps arising from Cs+ or I− vacancies. Additionally, these highly п-conjugated delocalized molecules can contribute to the efficient charge transport and prevent ions accumulation at the interface. As a result, sulfur-contained aminothiazolium iodide (ATI) post-treated CsPbI2Br devices showed simultaneous enhanced current density and voltage due to its higher interaction with perovskite lattice, this led to a champion efficiency of 13.91% with superb fill factor of more than 80%, which exhibited dramatic enhancement compared with the control samples (10.12%). Furthermore, surface passivation with delocalized molecules could effectively stabilize CsPbI2Br phase at room temperature or 80 °C annealing in ambient condition (65% RH). Equally important, this surface passivation allowed competitive efficiency of 11.26% with a large-area device (1.00 cm2). This high kill tolerant approach provide a new route to fabricate inorganic perovskite devices with higher efficiency and stability.

Europium and Acetate Co-doping Strategy for Developing Stable and Efficient CsPbI2 Br Perovskite Solar Cells.

All-inorganic perovskite solar cells have developed rapidly in the last two years due to their excellent thermal and light stability. However, low efficiency and moisture instability limit their future commercial application. The mixed-halide inorganic CsPbI2 Br perovskite with a suitable bandgap offers a good balance between phase stability and light harvesting. However, high defect density and low carrier lifetime in CsPbI2 Br perovskites limit the open-circuit voltage (Voc < 1.2 V), short-circuit current density (Jsc < 15 mA cm-2 ), and fill factor (FF < 75%) of CsPbI2 Br perovskite solar cells, resulting in an efficiency below 14%. For the first time, a CsPbI2 Br perovskite is doped by Eu(Ac)3 to obtain a high-quality inorganic perovskite film with a low defect density and long carrier lifetime. A high efficiency of 15.25% (average efficiency of 14.88%), a respectable Voc of 1.25 V, a reasonable Jsc of 15.44 mA cm-2 , and a high FF of 79.00% are realized for CsPbI2 Br solar cells. Moreover, the CsPbI2 Br solar cells with Eu(Ac)3 doping demonstrate excellent air stability and maintain more than 80% of their initial power conversion efficiency (PCE) values after aging in air (relative humidity: 35-40%) for 30 days.

High Efficiency (16.37%) of Cesium Bromide—Passivated All‐Inorganic CsPbI2Br Perovskite Solar Cells

All‐inorganic CsPbI2Br perovskite has attracted increasing attention, owing to its outstanding thermal stability and suitable bandgap for optoelectronic devices. However, the substandard power conversion efficiency (PCE) and large energy loss (Eloss) of CsPbI2Br perovskite solar cells (PSCs) caused by the low quality and high trap density of perovskite films still limit the application of devices. Herein, the post‐treatment of evaporating cesium bromide (CsBr) is utilized on top of the perovskite surface to passivate the CsPbI2Br–hole‐transporting layer interface and reduce Eloss. The results of microzone photoluminescence indicate that the evaporated CsBr gathered at the grain boundaries of CsPbI2Br layers and Br‐enriched perovskites (CsPbIxBr3−x, x &lt; 2) are formed, which can provide protection for CsPbI2Br. Therefore, the gaps between crystal grains are filled up, and the recombination loss of the all‐inorganic CsPbI2Br PSCs is reduced accordingly. The champion device exhibits high open‐circuit voltage and a PCE of 1.271 V and 16.37%, respectively. This is the highest reported PCE among all‐inorganic CsPbI2Br PSCs reported so far. In addition, the stability of CsPbI2Br PSCs is effectively improved by CsBr passivation, and the device without encapsulation can retain 86% of its initial PCE after 1368 h of storage, which is beneficial for practical applications.

High-performance carbon electrode-based CsPbI2Br inorganic perovskite solar cell based on poly(3-hexylthiophene)-carbon nanotubes composite hole-transporting layer

CsPbI2Br inorganic perovskite has been considered as a promising candidate for application in photovoltaic devices due to its high thermal stability and reasonable bandgap of 1.92 eV. However, CsPbI2Br perovskite is sensitive to moisture, which remarkably deteriorates the stability of CsPbI2Br perovskite solar cells under the ambient conditions. Here, by using hydrophobic poly(3-hexylthiophene) (P3HT) layer in conjunction with multi-walled carbon nanotubes (MWCNTs) as the hole transporting layer, we develop a stable and high-performance carbon electrode-based CsPbI2Br inorganic perovskite solar cell (PSC). The P3HT-MWCNTs composites not only can prevent moisture ingress but also enhance the holes extraction and transport. A conversion efficiency up to 10.01% with a stabilized efficiency of 8.85% is achieved for the champion device. In addition, the as-prepared carbon electrode-based CsPbI2Br PSC exhibits an excellent long-term stability which retains ∼85% of its initial value over 240 h under the ambient conditions (∼35% R.H.) without encapsulation.