Efficient Charge Extraction Research Articles

Precise control of PbI2 excess into grain boundary for efficacious charge extraction in off-stoichiometric perovskite solar cells

Excess PbI2 has been widely introduced in halide perovskite precursor solution to passivate the grain boundary defects in high efficient perovskite solar cells (PSCs). However, the passivation effect is highly sensitive to the PbI2 content and overmuch PbI2 affects the crystalline growth and charge transport. We report here a precious control of excess PbI2 into perovskite grain boundaries by methylamine treatment for efficacious defects passivation and charge extraction. The crystallization of the deposited perovskite films was carefully evaluated and the charge recombination dynamics were systematically analyzed through time-resolved photoluminescence spectroscopy, space charge limited current, electrochemical impedance spectroscopy and Mott-Schottky analysis. The precise PbI2 introduction to the grain boundaries results in a significantly lower defect state density, efficient charge extraction and prolonged carrier lifetime, causing a notable increase of short-circuit current density and negligible hysteresis in the corresponding device. Our work demonstrates a reliable method to alleviate the rigorous tolerance of PbI2 excess in high efficient PSCs.

Quantum dot-modified titanium dioxide nanoparticles as an energy-band tunable electron-transporting layer for open air-fabricated planar perovskite solar cells

Perovskite solar cells have been attracted as new representatives for the third-generation photovoltaic devices. Simple strategies for high efficiency with the long-term stability of solar cells are the challenges for commercial solar cell technology. Another challenge of the development toward industrial scale in perovskite solar cells is the production under the ambient and high humidity. In this sense, we successfully fabricated perovskite solar cells via solution depositions of all layers under ambient air with a relative humidity above 50%. Titanium dioxide (TiO2) nanoparticles with the roles for efficient charge extraction and electron transportation properties were used as an electron-transporting layer in the cell fabrication. The modification of TiO2 nanoparticles for energy band adjustment was done by doping with nontoxic cadmium sulfide (CdS) quantum dots. With the variation of CdS concentrations, energy band is not only changeable, but the enhancement of the perovskite solar cells efficiency could be achieved compared with the conventional cells made of pristine-TiO2 film and TiO2 nanoparticles.

Tracking Intrinsic Properties of CH3NH3PbI3 Perovskite Thin Films Grown by Spin Coating Technique at Ambient Temperature

Methyl ammonium lead iodide has become a burgeoning class of hybrid halide perovskites of solution-processed semiconductors. Advancements in its processing and characterization underscore structural, optical, and electronic properties. They have led to the development of perovskite solar cells, photo detectors, lasers, and photo diodes with power conversion efficiencies mature to be classified as first and second-generation technologies. Characterizing forms an integral understanding the operating principles and fundamental limitations for optoelectronics applications. Studies outlined in this paper covers CH3NH3PbI3 using time-resolved pump-probe spectroscopy, X-ray diffractometry, spectrophotometry and other measurements. Thus this investigatiosn may serve as principle tool in analyzing excited state decay kinetics and optical nonlinearities in CH3NH3PbI3 thin films. It is demonstrated herein that non-resonant photoexcitation yields a large fraction of free carriers on a sub-picosecond time scale. If applied in practical optoelectronic applications then any photogenerated carriers may travel long carrier lengths before they are extracted to realize large external quantum efficiencies and efficient charge extraction. The optical constants of CH3NH3PbI3 are interpreted using ab initio calculations through models. Findings show good agreement between the optical constants derived from QSGW and those from related literature. Transition from the highest valence band (VB) to the lowest conduction band (CB) was found to be responsible for almost all the optical responses between 1.2 and 5.5 eV. It was concluded that optical constants and energy band diagrams of CH3NH3PbI3 can be used to simulate the contributions from different optical transitions to a typical transient absorption spectrum for many optoelectronic applications.

Potassium-Presenting Zinc Oxide Surfaces Induce Vertical Phase Separation in Fullerene-Free Organic Photovoltaics.

Bulk heterojunction (BHJ) structure based organic photovoltaics (OPVs) have recently showed great potential for achieving high power conversion efficiencies (PCEs). An ideal BHJ structure would feature large donor/acceptor interfacial areas for efficient exciton dissociation and gradient distributions with high donor and acceptor concentrations near the anode and cathode, respectively, for efficient charge extraction. However, the random mixing of donors and acceptors in the BHJ often suffers the severe charge recombination in the interface, resulting in poor charge extraction. Herein, we propose a new approach-treating the surface of the zinc oxide (ZnO) as an electron transport layer with potassium hydroxide-to induce vertical phase separation of an active layer incorporating the nonfullerene acceptor IT-4F. Density functional theory calculations suggested that the binding energy difference between IT-4F and the PBDB-T-2Cl, to the potassium (K)-presenting ZnO interface, is twice as strong as that for IT-4F and PBDB-T-2Cl to the untreated ZnO surface, such that it would induce more IT-4F moving toward the K-presenting ZnO interface than the untreated ZnO interface thermodynamically. Benefiting from efficient charge extraction, the best PCEs increased to 12.8% from 11.8% for PBDB-T-2Cl:IT-4F-based devices, to 12.6% from 11.6% for PBDB-T-2Cl:Y1-4F-based devices, to 13.5% from 12.2% for PBDB-T-2Cl:Y6-based devices, and to 15.7% from 15.1% for PM6:Y6-based devices.

Efficient Bifacial Passivation with Crosslinked Thioctic Acid for High-Performance Methylammonium Lead Iodide Perovskite Solar Cells.

Defects, inevitably produced within bulk and at perovskite-transport layer interfaces (PTLIs), are detrimental to power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). It is demonstrated that a crosslinkable organic small molecule thioctic acid (TA), which can simultaneously be chemically anchored to the surface of TiO2 and methylammonium lead iodide (MAPbI3 ) through coordination effects and then in situ crosslinked to form a robust continuous polymer (Poly(TA)) network after thermal treatment, can be introduced into PSCs as a new bifacial passivation agent for greatly passivating the defects. It is also discovered that Poly(TA) can additionally enhance the charge extraction efficiency and the water-resisting and light-resisting abilities of perovskite film. These newly discovered features of Poly(TA) make PSCs herein achieve among the best PCE of 20.4% ever reported for MAPbI3 with negligible hysteresis, along with much enhanced ultraviolet, air, and operational stabilities. Density functional theory calculations reveal that the passivation of MAPbI3 bulk and PTLIs by Poly(TA) occurs through the interaction of functional groups (COOH, CS) in Poly(TA) with under-coordinated Pb2+ in MAPbI3 and Ti4+ in TiO2 , which is supported by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.

Role of Molecular and Interchain Ordering in the Formation of a δ-Hole-Transporting Layer in Organic Solar Cells.

Interface engineering, especially the realization of Ohmic contacts at the interface between organic semiconductors and metal contacts, is one of the essential preconditions to achieve high-efficiency organic electronic devices. Here, the interface structures of polymer/fullerene blends are correlated with the charge extraction/injection properties of working organic solar cells. The model system-poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM)-is fabricated using two different degrees of P3HT regioregularity to alter the blend interchain order and molecular packing, resulting in different device performances. Investigations by electroabsorption spectroscopy on these devices indicate a significant reduction (≈1 V) in the built-in potential with an increase in the P3HT regioregularity. This observation is also supported by a change in the work function (WF) of high regioregular polymer blends from photoelectron spectroscopy measurements. These results confirm the presence of a strong dipole layer acting as a δ-hole-transporting layer at the polymer/MoO3/Ag electrode interface. Unipolar hole-only devices show an increase in the magnitude of the hole current in high regioregular P3HT devices, suggesting an increase in the hole injection/extraction efficiency inside the device with a δ-hole-transporting layer. Microscopically, near-edge X-ray absorption fine structure spectroscopy was conducted to probe the surface microstructure in these blends, finding a highly edge-on orientation of P3HT chains in blends made with high regioregular P3HT. This edge-on orientation of P3HT chains at the interface results in a layer of oriented alkyl side chains capping the surface, which favors the formation of a dipole layer at the polymer/MoO3 interface. The increase in the charge extraction efficiency due to the formation of a δ-hole-transporting layer thus results in higher short circuit currents and fill factor values, eventually increasing the device efficiency in high regioregular P3HT devices despite a slight decrease in cell open circuit voltage. These findings emphasize the significance of WF control as a tool for improved device performance and pave the way toward interfacial optimization based on the modulation of fundamental polymer properties, such as polymer regioregularity.

Improving the efficiency and stability of inverted perovskite solar cells by CuSCN-doped PEDOT:PSS

Hole transport layer (HTL) is important in inverted perovskite solar cells (PSCs) to facilitate the hole extraction and suppress the charge recombination for high device performance. Based on the widely used HTL material of poly(ethylenedioxythiophene) (PEDOT):poly(styrenesulfonate) (PSS), we proposed a new HTL modification method using the widely available copper(I) thiocyanate (CuSCN); the doping of CuSCN NH3 [aq] in PEDOT:PSS followed by low-temperature annealing results in reduced energy barrier, improved charge extraction efficiency and increased the mean size of perovskite crystal of the PEDOT:PSS-CuSCN HTL-based inverted PSCs. Significantly improved device performance was observed with open current voltage over 1.0 V and power conversion efficiency (PCE) up to 15.3%, which is 16% higher in PCE than that of the PEDOT:PSS-based PSCs. More impressively, with a lower acidity than PEDOT:PSS, the PEDOT:PSS-CuSCN HTL enables excellent long-term stability of the inverted PSCs, exhibiting almost doubly improved device stability at the same storage condition. Thus, the successful application of CuSCN doping in PEDOT:PSS HTLs should provide a novel approach for the development of high-performance HTLs for highly efficient and stable PSCs.

Improving Photovoltaic Performance Using Perovskite/Surface‐Modified Graphitic Carbon Nitride Heterojunction

Passivation strategies are considered as one of the most efficient methods to suppress nonradiative recombination of organic–inorganic lead halide perovskite solar cells (PSCs), leading to tremendous photovoltaic performance. An innovative 2D polymer, graphitic carbon nitride (g‐C3N4), as well as various organic groups (amino, sulfonic, nitrato, and hydroxy group), are widely used as passivation agents, according to the previous reports. Anchoring g‐C3N4 and the aforementioned organic groups as additives in perovskite can both heal charged defects around the grain boundaries by passivating the charge recombination center. In addition, the crystalline quality can also be enhanced by the incorporation of g‐C3N4, leading to improved conductivity of perovskite light absorber films that is beneficial for benign charge extraction efficiency. Inspired by the underlining mechanisms, a series of novel passivation molecules, functionalized g‐C3N4 (F‐C3N4) with assorted organic groups, is designed herein, yielding a champion power conversion efficiency (PCE) of 20.08% for NO3‐C3N4‐based p‐i‐n structure PSC, in comparison with that of PSC without passivation (17.85%). These findings present an efficient strategy to understand and design multiple facets of applications of novel passivation molecules to further improve the PCE of PSCs.

Efficient and stable perovskite solar cells thanks to dual functions of oleyl amine-coated PbSO4(PbO)4 quantum dots: Defect passivation and moisture/oxygen blocking

The defects in perovskite crystals and the penetration of moisture/oxygen into the perovskite layer are major problems for perovskite solar cells (PSCs) to achieve long-term stability and high power conversion efficiency (PCE). However, there is still a lack of multifunctional passivation materials to solve these problems. Herein, for the first time, we report oleyl amine-coated PbSO4(PbO)4 quantum-dots (QDs), as a passivation material with dual functions to simultaneously passivate the surface defects and block the penetration of moisture/oxygen into the perovskite layer for stable and efficient PSCs. The PbSO4(PbO)4 QDs significantly reduce the defect density of the as-prepared CH3NH3PbI3 films by passivating under-coordinated Pb ions and I anions and effectively enhance charge extraction efficiency at the TiO2/CH3NH3PbI3 and CH3NH3PbI3/spiro-OMeTAD interfaces. Moreover, the hydrogen bond between H atoms of the OA and I atoms of the perovskite and the interface electric field at CH3NH3PbI3/OA interface also contribute to the improvement of efficiency and stability of PSCs. Finally, higher PCE (20.02%) is achieved by the PSCs with OA-coated PbSO4(PbO)4 QDs compared to that (16.86%) of the PSCs without OA-coated PbSO4(PbO)4, corresponding to a 18.7% enhancement. Moreover, the PSCs with OA-coated PbSO4(PbO)4 QDs maintain 90% of initial efficiency after operation for 280 h, indicating better stability than the PSCs without PbSO4(PbO)4 QDs.

Probing Charge Carrier Transport and Recombination Pathways in Monolayer MoS2/WS2 Heterojunction Photoelectrodes.

Monolayer heterojunctions such as MoS2/WS2 are attractive for solar energy conversion applications because the interfacial electric field spatially separates charge carriers in less than 100 fs. Photoelectrochemical cells represent an intriguing platform to collect the spatially separated carriers. However, the recombination, transport, and interfacial charge transfer processes that take place following the ultrafast charge separation step have not been investigated. Here we demonstrate novel charge recombination and transport pathways in monolayer MoS2/WS2 photoelectrochemical cells by spatially resolving the net collection of carriers (i.e., the photocurrent) at the single nanosheet level. We discovered an excitation-wavelength-dependent recombination pathway that depends on the heterojunction stacking configuration and the carrier generation profile in the heterostructure. Photocurrent mapping measurements revealed that charge transport occurs parallel to the layers over micrometer-scale distances even though the indium tin oxide electrode and liquid electrolyte provide efficient charge extraction pathways via intimate electron- and hole-selective contacts. Our results reveal how composition heterogeneity influences the performance of bulk heterojunction electrodes made from randomly oriented nanosheets and provide critical insight into the design of efficient heterojunction photoelectrodes for solar energy conversion applications.

In situ construction of gradient heterojunction using organic VOx precursor for efficient and stable inverted perovskite solar cells

Inverted perovskite solar cells (PSCs) have attracted tremendous attention recently but the energy levels between the perovskite absorber and conventional hole transport layers (HTL) are mismatch, resulting in the lower open-circuit voltages (Voc) than that of regular PSCs. Herein, a gradient heterojunction (GHJ) based on poly (3,4−ethylenedioxythiophene: polystyrenesulphonate) (PEDOT:PSS)/PEDOT:PSS-VOx was constructed in situ by low-temperature annealing and used as HTL of the inverted PSCs. This GHJ structure fabricated conveniently by doping a small amount of triisopropoxyvanadium oxide isopropyl alcohol solution into the PEDOT:PSS solution during spin-coating can efficiently facilitate charge separation and improve charge extraction efficiency, leading to significantly improved PSC performance with Voc up to 1.02 V and power conversion efficiency (PCE) to 18.0%. More impressively, owing to the more hydrophobic surface and lower acidity than the PEDOT:PSS layer after the formation of high work function VOx mainly on the surface of HTL, the GHJ-based PSCs show excellent long-term stability, which retain over 80% or 70% of their initial PCEs after exposure to full spectrum illumination in N2 for 750 h or in air for 175 h, respectively. These results illustrate the significant advantages of the in situ formed VOx-modified HTLs in gradient structures using organic VOx precursors, providing important clues in constructing GHJ for inverted PSCs with high efficiency and stability.

An Alcohol-Soluble Polymer Electron Transport Layer Based on Perylene Diimide Derivatives for Polymer Solar Cells

A conjugated alcohol-soluble polymer based on perylene diimide (PDI) and fluorene (PPDI-FN) was designed and synthesized. PPDI-FN can be soluble in methanol solution under the existence of tiny acetic acid, providing a possibility to prepare polymer solar cells (PSCs) by low-cost non-interfacial mixed solution method. The conventional PSCs based on PTB7-Th:PC71BM were fabricated with PPDI-FN as electron transport layer (ETL). Compare with PSCs based on PTB7-Th:PC71BM without ETL, the introduction of PPDI-FN can achieve an enormous enhancement in performance: V oc (open circuit voltage) from 0.75 to 0.80 V, J sc (short-circuit current density) from 15.57 to 16.72 mA/cm2, fill factor) from 55.96% to 68.87%, and power conversion efficiencies from 6.53% to 9.21%, which is better than PFN (8.62%) as an ETL. The performance of PPDI-FN in the device was studied; the results showed a decreased work function and increased electron transportation and conductivity, which are benefits for the cathode to enhance charge extraction efficiency and decrease recombination losses. These results showed that PDIs derivative PPDI-FN has good application prospects as an ETL to realize high-efficient PSCs.

Rare earth ions doped NiOx hole transport layer for efficient and stable inverted perovskite solar cells

Hole transport layer plays a critical role in achieving high performance and stable inverted perovskite solar cells (PSCs). Doping has been proved to be an effective strategy to modify the electrical and optical properties of semiconductor oxides. Herein, rare earths (REs: Ce, Nd, Eu, Tb, and Yb) elements are systemically doped into the NiOx hole transport layer (HTL) via a simple solution-based method. The results demonstrate that the REs doping could considerably modify the compactness, conductivity, and band alignment of the NiOx HTL, leading to the highly improved permanence of the inverted PSCs. The PSCs using 3% Eu:NiOx HTL yielded the optimum power conversion efficiency of 15.06%, relatively improved 23.4% compared with the PSC using pristine NiOx HTL (12.20%). It also demonstrated much better long time stability. The improved photovoltaic properties of the device can be attributed to the more efficient charge extraction and suppressed interfacial recombination rate by the introduction of appropriate REs in the NiOx HTL. This work indicates that RE doping is a very effective and promising strategy to achieve adjustable hole extraction material for high and stable inverted PSCs.

Conjugated Organic Cations Enable Efficient Self-Healing FASnI3 Solar Cells

Summary The introduction of large-volume amines (LVAs) in Sn-based perovskite films has been shown to lead to promising power conversion efficiency (PCE) in Pb-free perovskite solar cells (PSCs). However, the LVAs adopted so far (e.g., phenylethylammonium [PEA] and butylammonium [BA]) are insulating and could impede charge extraction within the perovskite film. Herein, a conjugated LVA, 3-phenyl-2-propen-1-amine (PPA), is introduced in formamidinium tin iodide (FASnI3) perovskite. Our results show that the incorporation of PPA results in enlarged grain sizes, reduced trap density, preferential orientation, efficient charge extraction, and enhanced structural stability of FASnI3 film. These positive effects help in achieving efficient PSCs with a PCE as high as 9.61% with negligible hysteresis and outstanding stability (remains 92% of its initial PCE value after 1,440 h). Furthermore, the presence of PPA enables a self-healing action of PSCs. Most importantly, we report large-area (1 × 1 cm2) Sn-based PSCs achieving PCE of 7.08%.

Spatially Resolved Carrier Dynamics at MAPbBr3 Single Crystal-Electrode Interface.

Despite the rapid progress in organic-inorganic halide perovskites (OIHPs) for applications such as solar cells and detectors, knowledge of coupling between electronic and ionic charge carrier dynamics is so far limited. While the presence of dual-conduction channels is widely accepted, the precise physical mechanisms governing the impact of electronic (e.g. electrons and holes) and ionic conduction, especially interface phenomena, remain uncertain. The lack of understanding stems largely from the lack of appropriate tools to capture the electrochemical dynamics on the length scales of the local inhomogeneities present (e.g., interfaces, grain boundaries, space charge regions) and time scales over which the coupled dynamics take place. Here, we implement Kelvin probe force microscopy (KPFM) to explore the charge carrier dynamics at the methylammonium lead tribromide (MAPbBr3) single crystal-gold electrode interface. In this work, the temporal dynamics of the electric field and charge carrier distribution at the electrode interface is spatially visualized by time-resolved KPFM mapping. The results demonstrate an interplay of several phenomena, including charge injection, recombination, and ion migration, leading to an unbalanced charge dynamic at MAPbBr3 single crystal-electrode interface under forward and reverse bias conditions explaining the origin of the current-voltage hysteresis in these devices. We contrast the bias-assisted charge dynamics under both illuminated and dark conditions, providing a comprehensive picture of overall carrier dynamics and interface properties in a MAPbBr3 single crystal with lateral symmetric Au electrodes. Remarkably, illumination leads to the formation of a wider space charge region due to accumulation of negative charges (both electrons and halide ions) at the positive electrode, which can effectively screen the external electric field leading to lower charge extraction efficiency. The results suggest that the choice of contact or interfacial engineering can control the performance of OIHP devices without requiring modification of the material's bulk properties.

Thermal annealing dependent dielectric properties and energetic disorder in PffBT4T-2OD based organic solar cells

Organic photovoltaics (OPV) has emerged as a promising renewable energy generation technology in the past decades. The thermal annealing effect on organic solar cells as one of the most widely used processing technologies have been substantially investigated. However, to the best of our knowledge, no research has investigated the changes in dielectric property and energetic disorder behind the thermal annealing processes. Herein, we conducted a systematic thermal annealing study for PffBT4T-2OD: PC71BM based organic solar cell and focused on the changes in dielectric property and energetic disorder. The characterisations such as J-V, EQE, PL, C–V, SCLC, AFM and TEM have been conducted for investigation. We systematically studied the annealing temperature up to 140 °C. It was found that devices annealed at 80 °C possess the most efficient exciton dissociation and charge extraction process and the highly suppressed the charge recombination which may be ascribed to its optimized interpenetrate morphology with optimized phase separation and domain size. The 80 °C annealed devices showed the largest dielectric constant and lowest capture coloumbic radius (Rc) among all devices which indicates that the optimized thermal annealing can tune the dielectric property of the device and induce more efficient charge separation. Moreover, we firstly estimated the annealing temperature-dependent Urbach energy. As results, all thermal annealed devices showed a reduced Urbach energy when compared to fresh devices, which proved that the thermal annealing process owns the ability to reduce the energetic disorder in the device.

Ruddlesden–Popper 2D Component to Stabilize γ‐CsPbI3 Perovskite Phase for Stable and Efficient Photovoltaics

AbstractThe highest certified power conversion efficiency (PCE) of black phase based CsPbI3 perovskite solar cells has exceeded 18%, and become a hotspot in recent progress. However, the black phase of CsPbI3 rapidly transforms to yellow phase in ambient conditions due to its thermodynamic instability. Here, a Ruddlesden–Popper 2D structure is introduced into γ‐CsPbI3 film to stabilize the black phase via reducing dimensionality. It is found that a judicious amount of phenylethylammonium iodide can adjust the dimensionality of γ‐CsPbI3 film from 2D to quasi‐2D and 3D phase. Comprehensive consideration to obtain both the stability and high PCE, quasi‐2D (n = 40) γ‐CsPbI3 delivers a reproducible PCE of 13.65% with negligible hysteresis. By utilizing femtosecond transient absorption and time‐resolved PL decay, similar carrier kinetics in n = 40 and ∞ samples are observed, meaning an efficient charge extraction. More importantly, when the device is placed at 80 °C in N2 condition or in air with RH of 25–30%, its PCE keeps ≈88% and ≈89% of its initial PCE after 12 days, respectively. Such results are better than the 3D one (≈69% and ≈16%, respectively).

Trade‐Off between Exciton Dissociation and Carrier Recombination and Dielectric Properties in Y6‐Sensitized Nonfullerene Ternary Organic Solar Cells

Organic photovoltaics (OPVs) have emerged as a promising renewable energy generation technology in past decades. However, the deep understanding of the details in exciton dissociation and carrier recombination in ternary organic solar cells (OSCs) is still lacking. Herein, a novel ternary OSC based on a PTB7‐Th:Y6:ITIC blend with a power conversion efficiency (PCE) enhancement of 29% is reported. A trade‐off is surprisingly found to exist between the exciton dissociation and carrier recombination process. The addition of nonfullerene acceptor Y6 in the ternary blend is found to create an efficient exciton dissociation process but accelerates the free carrier recombination process. Dielectric properties are also studied for ternary OSCs. The addition of Y6 into the binary blend is found to tune down the dielectric constant of the active layer and as a result accelerates the carrier recombination. The best performance is obtained for PTB7‐Th:Y6(5 wt%):ITIC(95 wt%)‐based ternary devices. In addition to its balanced charge carrier mobility and efficient charge extraction process, PTB7‐Th:Y6(5 wt%):ITIC(95 wt%)‐based ternary devices reach a balance in the trade‐off between the exciton dissociation and carrier recombination process and thus achieve the highest short‐circuit current density (Jsc) value.

Improving performance and moisture stability of perovskite solar cells through interface engineering with polymer-2D MoS2 nanohybrid

Power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have surged unprecedently to exceeding 23.3% within few years of research. Stability of PSCs still remains the matter of concern. Here, we present an elegant, simple and facile way of enhancing the efficiency and moisture stability of PSCs through interface engineering using poly(3-hexylthiophene-2,5-diyl) − 2D molybdenum disulfide (P3HT-MoS2) nanohybrid. The incorporation of the new hole transporting material (HTM) results into drastic (41%) efficiency enhancement through efficient charge extraction. P3HT-MoS2 interface layer provides much better device stability than that of P3HT. Nonetheless, our results reveal that degradation induced traps are responsible for the reduction of photocurrent and hence the device performance.

Ionic selective contact controls the charge accumulation for efficient and intrinsic stable planar homo-junction perovskite solar cells

The under-coordinated ionic defects at the surface and grain boundaries of organic-inorganic halide perovskite always attract and trap the free carriers via the electrostatic force and accelerate the ions migration by defect vacancies channels, significantly limiting the charge extraction efficiency and intrinsic stability of perovskite solar cells (PSCs). Here, a novel strategy of ionic layer induced homo-junction perovskite reinforced the build in field (Ebi) is proposed to further decrease trap recombination and suppress the ions migration, thereby enhancing the power conversion efficiencies (PCEs) and intrinsic stability of PSCs. Experiments and theories certify that the adsorbed cations and anions will not only give rise to interface charge accumulation/depletion of perovskite, resulting in boarder distributed and reinforced Ebi, but also increased the interface ions vacancy migration barriers via the extra ionic interaction. As a result, the resultant n-i-p PSCs showed a record PCE of 20.88% among the organic electron transfer layer (ETL) and deliver a high stability of 88% after aged 60 days in atmosphere without encapsulation. Our findings provide a new insight to further eliminate the side effect of ionic defects and guide to design newly contact interface to minimize the trap recombination and ions motion induced intrinsic stability of PSCs.