Unencapsulated Perovskite Solar Cells Research Articles

Revealing and Inhibiting the Facet-related Ion Migration for Efficient and Stable Perovskite Solar Cells.

Ion migration is a major issue hindering the long-term stability of perovskite solar cells (PSCs). As an intrinsic characteristic of metal halide perovskite materials, ion migration is closely related to the atomic arrangement and coordination, which are the basic characteristic differences among various facets. Herein, we report the facet-related ion migration, and then achieve the inhibition of ion migration in perovskite through finely modulating the facet orientation. We show that the (100) facet is substantially more vulnerable to cationic migration than the (111) facet. The main reason for this difference in migration is that the cationic migration route in the (111) facet deviates from that in the (100) facet, which increases the active migration energy and weakens the contribution from the electric field during operation. We prepare a (111)-dominated perovskite film by incorporating a facile and green addition of water (H2O) into the antisolvent, further achieving a power conversion efficiency (PCE) of 26.0 % (25.4 % certification) on regular planar PSCs and 25.8 % on inverted PSCs. Moreover, the unencapsulated PSCs can maintain 95 % of their initial PCE after 3500-hours operation under simulated AM1.5 illumination at the maximum power point.

Revealing and Inhibiting the Facet‐related Ion Migration for Efficient and Stable Perovskite Solar Cells

Ion migration is a major issue hindering the long‐term stability of perovskite solar cells (PSCs). As an intrinsic characteristic of metal halide perovskite materials, ion migration is closely related to the atomic arrangement and coordination, which are the basic characteristic differences among various facets. Herein, we report the facet‐related ion migration, and then achieve the inhibition of ion migration in perovskite through finely modulating the facet orientation. We show that the (100) facet is substantially more vulnerable to cationic migration than the (111) facet. The main reason for this difference in migration is that the cationic migration route in the (111) facet deviates from that in the (100) facet, which increases the active migration energy and weakens the contribution from the electric field during operation. We prepare a (111)‐dominated perovskite film by incorporating a facile and green addition of water (H2O) into the antisolvent, further achieving a power conversion efficiency (PCE) of 26.0% (25.4% certification) on regular planar PSCs and 25.8% on inverted PSCs. Moreover, the unencapsulated PSCs can maintain 95% of their initial PCE after 3500‐hours operation under simulated AM1.5 illumination at the maximum power point.

High-Efficiency Perovskite Solar Cells with Improved Interfacial Charge Extraction by Bridging Molecules.

The interface between the perovskite layer and electron transporting layer is a critical determinate for the performance and stability of perovskite solar cells (PSCs). The heterogeneity of the interface critically affects the carrier dynamics at the buried interface. To address this, a bridging molecule, (2-aminoethyl)phosphonic acid (AEP), is introduced for the modification of SnO2/perovskite buried interface in n-i-p structure PSCs. The phosphonic acid group strongly bonds to the SnO2 surface, effectively suppressing the surface carrier traps and leakage current, and uniforming the surface potential. Meanwhile, the amino group influences the growth of perovskite film, resulting in higher crystallinity, phase purity, and fewer defects. Furthermore, the bridging molecules facilitate the charge extraction at the interface, as indicated by the femtosecond transient reflection (fs-TR) spectroscopy, leading to champion power conversion efficiency (PCE) of 26.40% (certified 25.98%) for PSCs. Additionally, the strengthened interface enables improved operational durability of ≈1400 h for the unencapsulated PSCs under ISOS-L-1I protocol.

Efficient and Stable Perovskite Solar Cells via Multi-Functional Guanylurea Phosphate Zwitterionic Bridging Strategy

Buried interface defects and residual stresses significantly impede further improvements in the efficiency and stability of perovskite solar cells (PSCs). Herein, a flame retardant guanylurea phosphate (GUP) with multisite anchors serves as the zwitterionic bridge between SnO2 and perovskite. The phosphate groups within GUP facilitate bridging between SnO2 and perovskite while concomitantly passivating bifacial defects, thereby significantly inhibiting non-radiative recombination at the buried interface. Simultaneously, the planar configuration of the amidinourea unit strengthens the binding of amino (–NH2) and carbonyl (C=O) groups with [PbI6]4−, which enhances perovskite structure stability and relieves residual stresses. Contributing to the zwitterionic bridging strategy of multi-functional flame retardant, the power conversion efficiency (PCE) of GUP-treated PSCs significantly increased from 21.23 % to 24.03 %, with an open-circuit voltage (VOC) of up to 1.172 V, and exhibited outstanding stability. Unencapsulated PSCs treated with GUP maintained about 93.86 % and 80.53 % of their original efficiency after 1200 h of aging in the air at 25 °C with 25 ± 5 % relative humidity (RH) and after 600 h of aging in the air at 85 °C and 10 ± 5 % RH, respectively.

Efficient and stable perovskite solar cells via oxalic acid doped SnO2 nanocrystals with surface-defect passivation

The electron extraction and transfer play a crucial role in high performance of perovskite solar cells (PSCs). Tin dioxide (SnO2), with the high electrical conductivity and low photocatalytic activity, has been reported to be one of the most advantageous electron-transporting layers (ETL) in PSCs. However, a large number of non-radiative recombination defects have been reported in SnO2, which are attributed to the low tunability and lower dispersibility. Here, we propose a ligand-assisted tuning strategy based on the oxalic acid (OA) modification to control the SnO2 film and interfacial structure. This strategy can effectively inhibit the particle aggregation of SnO2 film. In addition, the bonding interaction between CO in the ligand and Sn in SnO2 and Pb atoms in the perovskite reduces the interfacial contact impedance and enhances the electron extraction. As a result, an impressive PCE of 22.68 %, a fill factor exceeding 0.82 and a Voc of 1.15 V were successfully obtained. In addition, the unencapsulated PSCs can maintain an initial efficiency of 93 % upon exposure to ambient air for 500 h.

Lattice Strain Regulation and Halogen Vacancies Passivation Enable High-Performance Formamidine-Based Perovskite Solar Cells.

Formamidinium lead iodide (FAPbI3) perovskite has lately surfaced as the preferred contender for highly proficient and robust perovskite solar cells (PSCs), owing to its favorable bandgap and superior thermal stability. Nevertheless, volatilization and migration of iodide ions (I-) result in non-radiating recombination centers, and the presence of large formamidine (FA) cations tends to cause lattice strain, thereby reducing the power conversion efficiency (PCE) and stability of PSCs. To solve these problems, the lead formate (PbFa) is added into the perovskite solution, which effectively mitigates the halogen vacancy and provides tensile strain outside the perovskite lattice, thereby enhancing its properties. The strong coordination between the C═O of HCOO- and Pb-I backbones effectively immobilizes anions, significantly increases the energy barrier for anion vacancy formation and migration, and reduces the risk of lead ion (Pb2+) leakage, thereby improving the operation and environmental safety of the device. Consequently, the champion PCE of devices with Ag electrodes can be increased from 22.15% to 24.32%. The unencapsulated PSCs can still maintain 90% of the original PCE even be stored in an N2 atmosphere for 1440h. Moreover, the target devices have significantly improved performance in terms of light exposure, heat, or humidity.

Target therapy at buried interfaces toward efficient and stable inorganic perovskite solar cells

The enhancement of power conversion efficiency (PCE) of perovskite solar cells (PSCs) is critically affected by charge recombination induced by buried interface defects. In light of this, a simple and effective target therapy strategy has been developed by doping 4-(diphenylphosphino)benzoic acid (4DBA) molecules at the tin oxide (SnO2)/perovskite interface. The effects of 4DBA on carrier transport, perovskite growth, defect passivation, and PSCs properties were systematically investigated. It is illustrated that 4DBA molecules not only passivate oxygen vacancy (OV) defects on the SnO2 surface, enhancing the conductivity of the SnO2 film and accelerating electron transfer, but also passivate perovskite interface defects, thereby improving the quality of the perovskite film. Ultimately, the efficiency of CsPbBr3 device with 4DBA-modified buried interface increased from 8.87% to 10.78%, an improvement of 21.53%. Furthermore, the efficiency of CsPbI2Br increased from 12.83% to 14.44%, an improvement of 12.55%, further demonstrating the effectiveness and universality of this strategy. Excitingly, the unencapsulated PSCs exhibit excellent long-term stability under high relative humidity and high temperatures.

Halogenated Hole Selective Contact Enhances Interfacial Weak Bonding of Perovskite Solar Cells

AbstractWeak bonding between the perovskite and charge transport layers can lead to interfacial defects, hindering charge transfer and limiting the efficiency and stability of perovskite solar cells (PSCs). To address this issue, two halogenated spiro[fluorene‐9,9′‐xanthene]‐based molecules (SFX‐DM‐F and SFX‐DM‐Cl) are designed as an interfacial layer between perovskite and hole transport materials (HTMs). Both first‐principles simulations and experimental results are used to demonstrate that these halogenated interfacial layers improve the contact stability between perovskite's Pb(II) and HTMs, increasing the efficiency of charge transfer. The similar structure of interlayer to HTM also enhances the interfacial hole transfer integral, favoring effective hole transport. The PSCs based on SFX‐DM‐Cl achieve power conversion efficiencies of 24.8% (0.0625 cm2) and 23.1% (1 cm2). Even after 2000 h at a relative humidity of 15–20%, the unencapsulated PSC retains 94% of its initial efficiency. This work proposes the halogenated homologous HTMs as interfacial molecular bridges to optimize weak chemical bonds and hole transfer, thereby enabling efficient and stable PSCs.

Perovskite solar cells with self-disintegrating seeds deliver an 83.64 % fill factor

Large-seed-induced regulation significantly impacts perovskite film grain growth; however, it inadequately addresses stress and defect issues at the perovskite interface. To counter this, we introduce an innovative self-disintegrating seed approach, employing 2D (4-FBZA)2PbI4 perovskite to enhance the crystallization process. During perovskite crystal growth, (4-FBZA)2PbI4 could disintegrate and release 4-FBZA+ ions. These ions effectively anchor the perovskite interface and interact with FA+ and [PbI6]4- within the lattice, passivating defects and releasing detrimental stress. This strategy results in reduced nonradiative recombination and residual stress, culminating in perovskite solar cells (PSCs) achieving a champion power conversion efficiency (PCE) of 23.73 % and a remarkable fill factor of 83.64 %. Crucially, unencapsulated PSCs retain over 90 % of their initial PCE following 2000 h of exposure in ambient conditions at 25±5 °C and 60 % relative humidity.

Improving Buried Interface Contact by Bidentate Anchoring for Inverted Perovskite Solar Cells.

Nickel oxide (NiOx) is a promising hole transport layer (HTL) to fabricate efficient and large-scale inverted perovskite solar cells (PSCs) due to its low cost and superior chemical stability. However, inverted PSCs based on NiOx are still lagging behind that of other HTL because of the poor quality of buried interface contact. Herein, a bidentate ligand, 4,6-bis (diphenylphosphino) phenoxazine (2DPP), is used to regulate the NiOx surface and perovskite buried interface. The diphosphine Lewis base in the 2DPP molecule can coordinate both with NiOx and lead ions at NiOx/perovskite interface, leading to high-quality perovskite films with minimized defects. It is found that the inverted PSCs with 2DPP-modified buried interface exhibit double advantages of being both fast charge extraction and reduced nonradiative recombination, which is a combination of multiple factors including favorable energetic alignment, improved interface contact and strong binding between NiOx/2DPP and perovskite. The optimal PSC based on 2DPP modification yields a champion power conversion efficiency (PCE) of 21.9%. The unencapsulated PSC maintains above 75% of its initial PCE in the air with a relative humidity (RH) of 30-40% for 1000h.

In-situ defect passivation assisted three-step printing of efficient and stable formamidine-lead bromide solar cells

Perovskite solar cells (PSCs) emerge as the most promising photovoltaics (PV) for their high performance and potential convenient cost-effective production routes comparing to the sophomore PV technologies. The printed PSCs with simplified device architecture and fabrication procedures could further enhance the competitive strength of PSC technology. In this work, we present an in-situ defect passivation (ISDP) assisted full-printing of high performance formamidine-lead bromide (FAPbBr3) PSCs. Only three rapid printing steps are involved for electron transporting layer (ETL), perovskite and carbon to form a complete solar cell on the low-cost fluorine-doped tin oxide (FTO) substrate. Long-chain polymer monomethyl ether polyethylene glycol is particularly utilized as the ISDP passivator, leading to conformal coating on the rough FTO and defect passivation for both ETL and perovskite during printing. A high efficiency of 10.85% (certified 10.14%) and a high Voc up to 1.57 V are achieved for the printed device. The unencapsulated PSCs maintain above 90% of the initial efficiency after continuously heating at 85 °C for 1000 h and over 80% of the efficiency after the maximum power point tracking for 3500 h. The fully printed semitransparent PSCs with carbon grids (CGs) show average visible light transmittance over 33% and an efficiency of 8.81%.

Synergetic Exterior and Interfacial Approaches by Colloidal Carbon Quantum Dots for More Stable Perovskite Solar Cells Against UV.

The achievement of both efficiency and stability in perovskite solar cells (PSCs) remains a challenging and actively researched topic. In particular, among different environmental factors, ultraviolet (UV) photons play a pivotal role in contributing to device degradation. In this work, by harvesting simultaneously both the optical and the structural properties of bottom-up-synthesized colloidal carbon quantum dots (CQDs), a cost-effective means is provided to circumvent the UV-induced degradation in PSCs without scarification on their power conversion efficiencies (PCEs). By exploring and optimizing the number of CQDs and the different locations/interfaces of the solar cells where CQDs are applied, a synergetic configuration is achieved where the photovoltaic performance drop due to optical loss is completely compensated by the increased perovskite crystallinity due to interfacial modification. As a result, on the optimized configurations where CQDs are applied both on the exterior front side as an optical layer and at the interface between the electron transport layer and the perovskite absorber, unencapsulated PSCs with PCEs >20% are fabricated which can maintain up to ≈94% of their initial PCE after 100h of degradation in ambient air under continuous UV illumination (5mWcm-2).

Minimizing Voltage Losses via Synergistically Reducing Hetero-Interface Energy Offset for High Efficiency Perovskite Solar Cells.

The open circuit voltage (VOC) losses at multiple interfaces within perovskite solar cells (PSCs) limit the improvements in power conversion efficiency (PCE). Herein, a tailored strategy is proposed to reduce the energy offset at both hetero-interfaces within PSCs to decrease the VOC losses. For the interface of perovskite and electron transport layer where exists a mass of defects, it uses the pyromellitic acid to serve as a molecular bridge, which reduces non-radiative recombination and energy level offset. For the interface of perovskite and hole transport layer, which includes a passivator of PEAI, the detrimental effect (negative shift of work function) of PEAI passivation and optimizing the interface energy level alignment are neutralized by incorporating (2-(4-(bis(4-methoxyphenyl)amino)phenyl)-1-cyanovinyl)phosphonic acid. Owing to synergistically reduced hetero-interface energy offset, the PSCs achieve a PCE of 25.13%, and the VOC is increased from 1.134 to 1.174V. In addition, the resulting PSCs possess enhanced stability, the unencapsulated PSCs can maintain ≈96% and ≈97% of their initial PCE after 2000h of aging under ambient conditions and 210h under operation conditions.

Zn–Porphyrin Antisolvent Engineering‐Enhanced Grain Boundary Passivation for High‐Performance Perovskite Solar Cell

Perovskite solar cells (PSCs) represent a promising and rapidly evolving technology in the field of photovoltaics due to their easy fabrication, low‐cost materials, and remarkable efficiency improvements over a relatively short period. However, the grain boundaries in the polycrystalline films exhibit a high density of defects, resulting in not only heightened reactivity to oxygen and water but also hampered charge transport and long‐term stability. Herein, an approach involving Zn‐porphyrin (Zn‐PP)‐upgraded antisolvent treatment to enhance the grain size and meanwhile passivate grain boundary defects in FA0.95MA0.05PbI2.85Br0.15 perovskites is presented. The Zn‐PP molecules significantly improve structural and optical properties, effectively mitigating defects and promoting carrier transport at the perovskite/hole transport layer interface. The density functional theory simulation confirms that Zn‐PP forms a strong chemical bonding with the perovskite surface. With Zn‐PP passivation, the total density of state shifts to higher‐energy regions with molecular adsorption, especially near the valence and conduction band edges, indicating that there is an increase in conducting properties of the surface with molecular adsorption. The power conversion efficiency (PCE) of PSCs increases significantly as a result of this improvement, rising from 15.38% to 19.11%. Moreover, unencapsulated PSCs treated with Zn‐PP exhibit outstanding stability, retaining over 91% of their initial PCE.

A Universal and Versatile Hole Transport Layer “Activator” Enables Stable Perovskite Solar Cells with Efficiency Near 25%

AbstractOrganic small molecules have been proven to be the most efficient and predominantly employed hole transport layers (HTLs) in perovskite solar cells (PSCs), the reliance of HTLs on additives like Li‐TFSI has been unavoidable, particularly in terms of the well‐known Spiro‐OMeTAD. However, Li‐TFSI aggregation in HTL results in the decreased performance and stability of PSCs with serious hysteresis. It is an urgent need to explore a universal strategy to solve Li‐TFSI‐induced issues. Herein, a pyrene‐based organic semiconductor (PC) as an effective and universal additive for HTL application is developed. It is found that the introduction of PC can efficiently improve the hot carriers extraction/transfer and reduce the charge recombination in the device. Consequently, PSCs based on Spiro‐OMeTAD+PC as a HTL exhibit an excellent PCE of 24.80% with a negligible hysteresis, much higher than the control device (22.14%). Additionally, the efficiency of the PC incorporated into another well‐known X60 HTL‐treated device is enhanced to 24.12% from the control device (22.04%), confirming its universal application in PSCs. Moreover, PC can effectively suppress the Li+ aggregation in HTL, and the unencapsulated PSCs exhibit high stability. The findings in this work provide an effective and universal avenue to construct highly efficient and stable PSCs.

Fine optimized cation immobilization strategy for enhancing stability and efficiency of perovskite solar cells

The migration and volatilization of cations within organic–inorganic hybrid perovskite (OIPs) materials has been identified as a major issue for irreversibly degrading perovskite solar cells (PSCs), severely limiting their performance and impeding progress toward large-scale applications. To mitigate these problems, an adjustable cation immobilization strategy was proposed for the first time, in which a series of fluorobenzenesulfonamide (FBSA) molecules was introduced into perovskite precursor, a strong coordination bond was formed between the sulfonamide group with the octahedral imperfection caused by iodine vacancy, along with a hydrogen bond formed between the cation and F atom. As a result, the A-site cations were tightly immobilized in the octahedral of perovskite crystal lattice and the uncoordinated Pb2+ defects were effectively eliminated. Besides, the immobilization distance of cation was finely optimized by changing the substitution position of F atoms. Based on the cation-immobilized perovskite film, the efficiency of PSCs was significantly increased from 19.88 % to 22.30 %. Moreover, the unencapsulated PSCs exhibited impressive light and thermal stability, retaining 82 % of the initial efficiency after 720 h illumination at 1-sun, and maintaining nearly 80 % of the initial PCE after heating at 85 °C for 240 h. Thus, the present study offers a promising approach for advancing the commercialization of stable and high-efficiency perovskite solar cells.

Reinforced SnO2 tensile‐strength and “buffer‐spring” interfaces for efficient inorganic perovskite solar cells

AbstractSuppressing nonradiative recombination and releasing residual strain are prerequisites to improving the efficiency and stability of perovskite solar cells (PSCs). Here, long‐chain polyacrylic acid (PAA) is used to reinforce SnO2 film and passivate SnO2 defects, forming a structure similar to “reinforced concrete” with high tensile strength and fewer microcracks. Simultaneously, PAA is also introduced to the SnO2/perovskite interface as a “buffer spring” to release residual strain, which also acts as a “dual‐side passivation interlayer” to passivate the oxygen vacancies of SnO2 and Pb dangling bonds in halide perovskites. As a result, the best inorganic CsPbBr3 PSC achieves a champion power conversion efficiency of 10.83% with an ultrahigh open‐circuit voltage of 1.674 V. The unencapsulated PSC shows excellent stability under 80% relative humidity and 80°C over 120 days.

Enhanced Efficiency and Stability of Quasi Two-dimensional Perovskite Solar Cells via Dual Additives

Quasi two-dimensional alternating cation (ACI)-type perovskites have drawn extensive research interest owing to better stability than their 3D counterparts. However, the poor charge-transfer characteristics of quasi two-dimensional perovskite film significantly impact the efficiency and stability of the devices. Herein, we propose a dual additives strategy utilizing urea and methylammonium chloride to manage the growth of (GA)(MA)5Pb5I16 perovskite films. The morphology and photoelectric characteristics manifest that the dual additives not only significantly enlarge the crystal size of the film, but also optimize the distribution of the quantum well thickness. Therefore, the solar cell based on dual additives-treated perovskite film achieves an optimal efficiency of 20.86%, far higher than 17.11% for that without additive. Moreover, the environmental stability of the quasi two-dimensional perovskite solar cells (PSCs) is raised. The unencapsulated PSCs hold 93% of the initial efficiency after being placed under environmental conditions for 1500hours. These results demonstrate that using dual additives is a promising strategy to obtain high-performance PSCs.

One‐Step Construction of a Perovskite/TiO2 Heterojunction toward Highly Stable Inverted All‐Layer‐Inorganic CsPbI2Br Perovskite Solar Cells with 17.1% Efficiency

AbstractAll‐layer‐inorganic perovskite solar cells (PSCs) are prized for their remarkable thermal stability and low cost. However, “imperfect contact” at the perovskite heterojunction hinders charge transport and causes photochemical deterioration, restricting photovoltaic performance, and operational stability. Herein, an efficient perovskite/TiO2 heterojunction is constructed, produced by adding TiO2 to an antisolvent to concurrently form a CsPbI2Br perovskite layer and a top TiO2 electron transport layer in one step, which significantly improves the interfacial contact and thus facilitates charge transport at the heterojunction. The resultant inverted all‐layer‐inorganic PSCs exhibit a superior efficiency of 17.1%. Moreover, given the high‐quality perovskite/TiO2 heterojunction and low interface defects, the encapsulated PSCs retain 91% or 92% of their initial efficiency for 1000 h under maximum power point tracking or damp‐heat conditions (85 °C and 85% relative humidity), respectively. Surprisingly, the unencapsulated PSCs maintain an initial efficiency of 86% during aging, even at 200 °C for 200 h.

Thick film high-performance carbon-based CsPbIBr2 perovskite solar cells vis nano-perovskite modified hot casting method

All-inorganic carbon-based CsPbIBr2 perovskite solar cells (PSCs) have attracted attention due to their more balanced performance and stability. The performance of the PSCs is highly dependent on the quality of the absorber films. Unfortunately, most high-performance films are prepared in a glove box and conventional preparation methods often produce perovskite films within 400 nm of thickness, which is detrimental to large area device fabrication and limits their commercial application. Here we had demonstrated a short chain ligands nano-CsPbIBr2 particles modified hot-casting method to deposit a perovskite film with thickness up to 800 nm. It was carried out by spin-coating a hot CsPbIBr2 precursor solution onto nano-CsPbIBr2 particles film on an electron transport layer (ETL), and then depositing nano-CsPbIBr2 particles on the precursor film again before annealing. The nano-CsPbIBr2 particles on the ETL promotes precursor solution crystallization and increased film thickness, and the nano-CsPbIBr2 particles on the precursor film promoted grain growth and reduced defects due to compositional deviations from stoichiometric ratios. The power conversion efficiency (PCE) of the PSCs fabricated by this method is up to 10.66 %. The unencapsulated PSCs still retain more than 85 % of the initial PCE when stored at ambient atmosphere (RH 50–60 %) for 10 days.