MAPbI3 Perovskite Research Articles

Single-walled carbon nanotube as hole transport layer in perovskite solar cell: Efficiency enhancement

We propose a new hole transport layer (HTL) in a perovskite solar cell (PSC) using single-walled carbon nanotube (SWCNT) achieving a power conversion efficiency (PCE) up to 19.98%, for the first time. Owing to its exceptional quantum properties, this one-dimensional (1D) element is utilized in order to facilitate hole transport inside the cell structure. Using (6, 5) SWCNT as the HTL and the MAPbI3 perovskite material on top of it as the main adsorbent layer, while colloidal quantum dots (CQDs) of lead sulfide (PbS-CQDs) with excellent absorption in the wavelength range of 500–1100 nm fills the space around the SWCNTs in each unit cell as the second adsorbent layer, we achieved excellent performance. Also, we observe a 49.7% increase compared to when the space around the HTL is filled with perovskite material. The proposed PSC arrangement, due to its brilliant electrical and mechanical properties besides excellent stability of SWCNTs, gives significantly superior cell stability in addition to a high PCE. Finally, we hope that utilizing this novel structure can be extended in the industry along with solving problem of perovskite stability.

Phase transformations and vibrational properties of hybrid organic–inorganic perovskite MAPbI3 bulk at high pressure

The structural stability and internal properties of hybrid organic–inorganic perovskites (HOIPs) have been widely investigated over the past few years. The interplay between organic cations and inorganic framework is one of the prominent features. Herein we report the evolution of Raman modes under pressure in the hybrid organic–inorganic perovskite MAPbI_3 by combining the experimental approach with the first-principles calculations. A bulk MAPbI_3 single crystal was synthesized via inverse temperature crystallization (ITC) technique and characterized by Raman spectroscopy, while the diamond anvil cells (DACs) was employed to compress the sample. The classification and behaviours of their Raman modes are presented. At ambient pressure, the vibrations of inorganic PbI_6 octahedra and organic MA dominate at a low-frequency range (60–760 cm^{-1}) and a fingerprint range (900–1500 cm^{-1}), respectively. The applied pressure exhibits two significant changes in the Raman spectrum and indicates of phase transition. The results obtained from both experiment and calculations of the second phase at 3.26 GPa reveal that the internal vibration intensity of the PbI_6 octahedra (< 110 cm^{-1}) reduces as absences of MA libration (150–270 cm^{-1}) and internal vibration of MA (450–750 cm^{-1}). Furthermore, the hydrogen interactions around 1300 cm^{-1} remain strong high pressure up to 5.34 GPa.

Efficient MAPbI3-based perovskite solar cells exceeding 21% efficiency via aging treatment

Recently, the demand for large-area and high-efficiency perovskite solar cells (PSCs) has increased, and a two-step process for high-efficiency large-area PSCs is actively being studied. However, the two-step process is still less efficient than the one-step antisolvent dripping process owing to the poor interdiffusion of organic components. In this study, a perovskite layer using a hybrid deposition method in which an excess of methylammonium iodide (MAI) solution is reacted with thermally evaporated PbI2 is reported. The perovskite film quality is improved by reacting unreacted residual PbI2 with excess MAI by applying daily electrical stress and aging for 60 days in a glovebox. The best PSC exhibits a PCE of 21.1 %, the highest reported power conversion efficiency among PSCs based on the two-step hybrid deposited MAPbI3 perovskite, with a large enhanced open-circuit voltage of 1.21 V and fill factor of 80.8 %. Moreover, using the solvent pre-heat treatment method, the reaction of unreacted PbI2 with MAI is accelerated, and the aging time of PSCs is shortened from 60 to 7 days, showing a PCE value of 20.7 %. Furthermore, we present a large-area PSC with a PCE of 19.4 %, indicating that the PCE can be improved through the hybrid deposition method.

Structural and Optical Characterization of Spin-Coated Perovskite MAPbI3 – xBrx Nano-Needles

Structural and Optical Characterization of Spin-Coated Perovskite MAPbI3 – xBrx Nano-Needles

Strengthened Interficial Adhesive Fracture Energy by Young's Modulus Matching Degree Strategy in Carbon-Based HTM Free MAPbI3 Perovskite Solar Cell with Enhanced Mechanical Compatibility.

Carbon-based hole transport layer-free perovskite solar cells (PSCs) based on methylammonium lead triiodide (MAPbI3 ) have become one of the research focus due to low cost, easy preparation, and good optoelectronic properties. However, instability of perovskite under vacancy defects and stress-strain makes it difficult to achieve high-efficiency and stable power output. Here, a soft-structured long-chain 2D pentanamine iodide (abbreviated as "PI") is used to improve perovskite quality and interfacial mechanical compatibility. PI containing CH3 (CH2 )4 NH3 + and I- ions not only passivate defects at grain boundaries, but also effectively alleviate residual stress during high temperature annealing via decreasing Young's modulus of perovskite film. Most importantly, PI effectively increases matching degree of Young's modulus between MAPbI3 (47.1GPa) and carbon (6.7GPa), and strengthens adhesive fracture energy (Gc ) between perovskite and carbon, which is helpful for outward release of nascent interfacial stress generated under service conditions. Consequently, photoelectric conversion efficiency (PCE) of optimal device is enhanced from 10.85% to 13.76% and operational stability is also significantly improved. 83.1% output is maintained after aging for 720h at room temperature and 25-60% relative humidity (RH). This strategy of regulation from chemistry and physics provides a strategy for efficient and stable carbon-based PSCs.

Probing surface dipole effects on perovskite photocurrent hysteresis through in-situ characterization

This study explored the impact of two dipole molecules, 4-nitrobenzoic acid and 4-aminobenzoic acid, on the electronic properties of MAPbI3 perovskite. Significant changes in the work function were observed upon molecular adsorption, with 4-nitrobenzoic acid increasing the work function and 4-aminobenzoic acid decreasing it. The lock-in amplifier based surface photovoltage spectroscopy measurements revealed that 4-nitrobenzoic acid decreased surface photovoltage, while 4-aminobenzoic acid increased it. Furthermore, in-situ conductive-atomic force microscopy analysis indicated pronounced photocurrent hysteresis with 4-aminobenzoic acid and reduced hysteresis with 4-nitrobenzoic acid. This study underscores the critical role of surface dipoles in manipulating perovskite charge transfer and provides valuable insights into the mechanisms behind photocurrent hysteresis.

High performance and stable perovskite solar cells modified with 8-hydroxyquinoline lead

The quality of the perovskite active layer is the critical factor that affects the photovoltaic performance of perovskite solar cells (PSCs). In this paper, the 8-hydroxyquinoline lead (Pbq2) containing pyridine bonds, C–O bonds, and quinoline ring groups was introduced into the MAPbI3 perovskite layer to improve the performances and stabilities of PSCs. The doped Pbq2 could adjust the growth of perovskite crystals by coordinating interactions between the above functional groups in Pbq2 with Pb2+, MA+, and I− in perovskite together. And as a result, high-quality and dense perovskite films with larger grain sizes were obtained. At the same time, large molecule-sized Pbq2 chelated at the grain boundary of perovskite, which passivated the defects and suppressed non-radiative recombination of photo carriers and ion migration at grain boundaries. Therefore, the interface energy barrier between the perovskite layer and the electron transfer layer (ETL) was reduced by the Pbq2 doping, which accelerated the separation and transportation of carriers at the ETL/perovskite layer interface. Finally, Pbq2-modified PSCs achieved a power conversion efficiency (PCE) of 20.82% with an open circuit voltage (Voc) of 1.144 V and a fill factor (FF) of 77.4% compared to a PCE of 17.87% for the reference sample. Furthermore, Pbq2-modified PSCs showed better light stability and moisture resistance in air conditions.

Sub-Bandgap Sensitization of Perovskite Semiconductors via Colloidal Quantum Dots Incorporation.

By taking advantage of the outstanding intrinsic optoelectronic properties of perovskite-based photovoltaic materials, together with the strong near-infrared (NIR) absorption and electronic confinement in PbS quantum dots (QDs), sub-bandgap photocurrent generation is possible, opening the way for solar cell efficiencies surpassing the classical limits. The present study shows an effective methodology for the inclusion of high densities of colloidal PbS QDs in a MAPbI3 (methylammonium lead iodide) perovskite matrix as a means to enhance the spectral window of photon absorption of the perovskite host film and allow photocurrent production below its bandgap. The QDs were introduced in the perovskite matrix in different sizes and concentrations to study the formation of quantum-confined levels within the host bandgap and the potential formation of a delocalized intermediate mini-band (IB). Pronounced sub-bandgap (in NIR) absorption was optically confirmed with the introduction of QDs in the perovskite. The consequent photocurrent generation was demonstrated via photoconductivity measurements, which indicated IB establishment in the films. Despite verifying the reduced crystallinity of the MAPbI3 matrix with a higher concentration and size of the embedded QDs, the nanostructured films showed pronounced enhancement (above 10-fold) in NIR absorption and consequent photocurrent generation at photon energies below the perovskite bandgap.

Facile Vertical Structure Broadband Photodetectors Enabled by Polyvinylpyrrolidone-Regulated Perovskite and Near-Infrared-Sensitive Lead Phthalocyanine.

Broadband photodetectors have drawn tremendous attention in many application areas such as imaging, optical communication, and biochemical sensing. Perovskite is a star material with broad spectral absorption, but it is challenging to develop ultraviolet-visible-near-infrared (UV-Vis-NIR) ultra-broadband photodetectors due to the insufficient absorption in the near-infrared region. Moreover, it is difficult to construct a diode-type photodetector with a simple vertical structure based only on perovskite materials. Here, facile vertical structure broadband photodetectors were fabricated based on heterojunctions that were composed of perovskite MAPbI3 films with UV-Vis absorption spectrum and small organic molecule lead phthalocyanine (PbPc) with strong NIR optical absorption, resulting in UV-Vis-NIR ultra-broadband photodetection. The quality of MAPbI3 films was improved by introducing polyvinylpyrrolidone (PVP) modification, and subsequently, the corresponding MAPbI3/PbPc heterojunction-based photodetectors exhibited rectification characteristics and reduced reverse dark currents. When the PVP mass ratio is 1 wt%, the photodetector achieved the best performance that the spectral response uniformity factor was as high as 0.77, the photoresponsivity exceeded 10 A/W, and the photoresponse time was less than 0.5 ms under a light intensity of 0.013 mW/cm2 in the UV-Vis to NIR spectral range. These results are comparable or superior to those of some inorganic, organic, and perovskite photodetectors reported previously. This study would provide an effective strategy to construct high-performance perovskite photodetectors based on a simple vertical structure, paving the way to the realization of UV-Vis-NIR broadband photodetection.

Tuned Transport Path of Perovskite MAPbI3-based Memristor Structure.

In this study, the features of resistive random access memory (RRAM) employing a straightforward Cr/MAPbI3/FTO three-layer structure have been examined and clarified. The device displays various resistance switching (RS) behavior at various sweep voltages between 0.5 and 5 V. The RS effect has a conversion in the direction of the SET and RESET processes during sweeping for a number of cycles at a specific voltage. The directional change of the RS processes corresponds to the dominant transition between the generation/recombination of iodide ion and vacancy in the MAPbI3 perovskite layer and the electrochemical metallization of the Cr electrode under the influence of an electric field, which results in the conductive filament (CF) formation/rupture. At each stage, these processes are controlled by specific charge conduction mechanisms, including Ohmic conduction, space-charge-limited conduction (SCLC), and variable-range hopping (VRH). By identifying the biased voltage and the quantity of voltage sweep cycles, one can take a new approach to control or modulate the pathways for effective charge transport. This new approach is made possible by an understanding of the RS characteristics and the corresponding mechanisms causing the variation of RS behavior in the structure.

Unraveling photo-induced charge transfer properties at 3D/2D perovskite interfaces via in-situ surface photovoltage spectroscopy

As a non-destructive and contactless characterization technique, the surface photovoltage (SPV) method based on a lock-in amplifier was applied to characterize charge transfer at the nanoscale of 3D/2D perovskite interface. The SPV response of the 3D/2D perovskite was found to be stronger than that of the 3D perovskite, suggesting improved separation and transfer of photo-induced electron-hole pairs by the 2D overlayer. The photovoltaic process can be presented as a vector diagram with the magnitude and the phase angles to unravel charge transfer direction. The magnitude of the overall photovoltaic vector increases with an anticlockwise rotation and confirms the hole transfer at 3D/2D perovskite interfaces. Moreover, light-chopping-frequency dependent measurements were performed to study photogenerated electron transfer kinetics at the 3D/2D interface. The frequency of peak SPV for 3D/2D MAPbI3 perovskite was higher than that of 3D MAPbI3 demonstrated a faster charge separation in 3D/2D interface. The results provide valuable information about the in-situ charge transfer properties of photogenerated charge carriers at the 3D/2D perovskite interfaces.

Improving the efficiency and stability in a MAPbI3 perovskite solar cell using dimensionally engineered PbS quantum dot passivation layer

Using a dimensionally engineered nano film of lead sulphide (PbS) above/below the methyl ammonium lead tri-iodide (MAPbI3) as a passivation layer in a planar inverted perovskite solar cell (PSC), we have shown that the power conversion efficiency (PCE) can increase at least by 3% compared to the reference MAPbI3 inverted perovskite solar cell. This improvement of 3% in efficiency using a PbS nano layer is better than any other reference reported in the literature. Further, with the incorporation of PbS nano film the fill factor (FF) showed a significant enhancement, reaching over 0.81. In addition, the effects of perovskite layer thickness, PbS layer thickness, and different optical parameters like absorbance, reflectance, transmittance, and temperature on the PCE are also investigated. The results of this investigation seem to be important for the realisation of low cost and more efficient solar cells based on PbS nano film and perovskite materials.

Effects of Co-Addition of Guanidinium and Cesium to CH3NH3PbI3 Perovskite Solar Cells

The effects of guanidinium (C(NH2)3, GA) and cesium (Cs) co-additions on methylammonium lead iodide (CH3NH3PbI3, MAPbI3) perovskite solar cells were investigated. The first-principles calculations on the density of the states and band structures showed a reduction in the total energy by the GA addition. Although the calculation showed that the co-addition of the GA/Cs to the MAPbI3 perovskite could decrease the carrier mobilities, and the addition of GA/Cs improved the device performance. This result would be due to a facilitation of grain growth and a suppression of the defects from the GA/Cs addition. The changes to the conversion efficiencies of the device with the best performance were small, which indicates that the present co-addition of GA/Cs is effective for the stability of the devices.

New Dication-Based Lead-Deficient 3D MAPbI3 and FAPbI3 "d-HPs" Perovskites with Enhanced Stability.

Toxicity induced by the presence of lead and the rather poor stability of halide perovskite semiconductors represent the major issues for their large-scale application. We previously reported a new family of lead- and iodide-deficient MAPbI3 and FAPbI3 perovskites called d-HPs (for lead- and iodide-deficient halide perovskites) based on two organic cations: hydroxyethylammonium HO-(CH2)2-NH3+ (HEA+) and thioethylammonium HS-(CH2)2-NH3+ (TEA+). In this article, we report the use of an organic dication, 2-hydroxypropane-1,3-diaminium (2-propanol 1,3 diammonium), named PDA2+, to create new 3D d-HPs based on the MAPbI3 and FAPbI3 network with general formulations of (PDA)0,88x(MA)1-0,76x[Pb1-xI3-x] and (PDA)1,11x(FA)1-1,22x[Pb1-xI3-x], respectively. These d-HPs have been successfully synthesized as crystals, powders, and thin films and exhibit improved air stability compared to their reference MAPbI3 and FAPbI3 perovskite counterparts. PDA2+-based deficient MAPbI3 was also tested in operational perovskite solar cells and exhibited an efficiency of 13.0% with enhanced stability.

Study of charge-transfer and energy-transfer properties of methylammonium-based-Pb-halide perovskites

The efficiencies of organic-inorganic halide perovskites have shown subjective increment in recent years, but the instability issues encumber their further development and applications. This article includes the synthesis of MAPbI3, MAPbICl2, and MAPbIClBr perovskites by one-step and two-step spin-coating methods. Further, we investigated the structural and optoelectronic properties of as-prepared perovskites and degraded perovskites after the degradation period (i.e., exposure to light, temperature, and humidity) of 30 days. Here, we also determined the structural & optoelectronic properties of as-prepared and degraded halide perovskite nanocrystals passivated by N, N-DMF and also studied their charge transfer & energy transfer characteristics by dissolving in MEH-PPV (poly(2-methoxy-5(2-ethylhexyloxy-1,4-phenylenevinylene)) polymer. Moreover, as-prepared MAPbI3 perovskite exhibits effective photoluminescence quenching evident from the highest stern-Volmer quenching constant (Ksv), enhancing charge-transfer efficiency in as-prepared MAPbI3:MEH-PPV composites. On the other hand, the energy-transfer process dominates between the host-polymer donor and guest perovskite as an acceptor due to the low PL quenching in degraded MAPbI3:MEH-PPV composites. However, as reported earlier, the stability of perovskite for LEDs is a challenging task. Still, in this manuscript, we stated that an inferior perovskite material for photovoltaics would prove to be a good perovskite material for LEDs applications.

Potassium hexacyanoferrate(III): A promising additive for perovskite precursors in carbon-based perovskite solar cells

Perovskite solar cells (PSCs) that use carbon electrodes and low-temperature processed electron transport layers (ETLs) show great promise in meeting global energy needs at an affordable price. Our current research is focused on the development of carbon-based perovskite solar cells (PSCs) that incorporate low-temperature titanium oxide electron transport layers (ETLs) to enhance their photovoltaic performance. In our approach, we introduce potassium hexacyanoferrate(III) material into the pre-solution of the MAPbI3 perovskite to fabricate a light-harvesting layer. This promising technique has shown great potential in improving the overall performance of PSCs. This additive reduces the formation of non-radiative recombination centers, resulting in a perovskite layer that is desirable and free from defects. Furthermore, photovoltaic devices based on potassium hexacyanoferrate(III) exhibit reduced transfer resistance, leading to faster charge transfer at the interfaces of TiO2/perovskite and perovskite/carbon electrodes. As a result, the efficiency of PSCs can be improved by up to 14.89%, which is significantly higher than the recorded efficiency of unmodified PSCs at 12.05%. In addition, PSCs based on potassium hexacyanoferrate show greater stability in ambient air compared to their unmodified counterparts.

Tailoring Precursor Chemistry Enabled Room Temperature‐Processed Perovskite Films in Ambient Air for Efficient and Stable Solar Cells with Improved Reproducibility

AbstractThe perovskite solar cells (PSCs) are promising for commercialization and practical application. However, high‐quality perovskite films are normally fabricated in inert gas‐filled glovebox, followed by thermal annealing, which is energy‐consuming and thus not cost‐effective. In this study, a simple manufacturing strategy is demonstrated to fabricate the highly‐crystalline perovskite films in ambient air (a relative humidity of over ≈50%) at room temperature via blade‐coating without the subsequent thermal–annealing. The perovskite precursor chemistry is tailored by solvent engineering via employing 2‐methoxyethanol, which can strongly coordinate with ammonium halide species, thus forming highly uniform small‐sized colloids and facilitating the homogeneous nucleation and rapid crystallization of perovskite films even at room temperature. The resultant PSCs fabricated with ambient‐processed, annealing‐free MAPbI3 perovskite films exhibit a champion efficiency up to 19.16% with negligible hysteresis and improved reproducibility, which is on par with the high‐temperature annealed counterparts fabricated in N2, and represented one of the highest reported efficiencies for the room‐temperature processed PSCs in ambient air. The unencapsulated devices show extended lifespan over 1000 h with nearly no efficiency loss.

Triphenylimidazole substituted D-π-D porphyrin based dopant-free hole transport materials for perovskite solar cells

Hole-transport materials (HTMs) contribute an important function in perovskite solar cells (PSCs) for achieving favourable photovoltaic performance with durability. In this work, we designed and synthesized a series of porphyrin based hydrophobic HTMs based on donor-π-donor (D-π-D) tactic in which triphenylimidazole as donor and either free-base porphyrin (H2LD) or metalloporphyrin (Cu, CuLD or Zn, ZnLD) as π-spacer for PSCs. All three HTMs were characterized by a variety of spectroscopic and electrochemical methods. Optical and electrochemical properties propose that the highest occupied molecular orbital (HOMO) energy levels were healthily aligned with the valence band of MAPbI3 perovskite. Among these HTMs, CuLD exhibited higher hole mobility of 7.39 × 10-5 cm2V-1s-1, when compared to ZnLD 5.77 × 10-5 cm2V-1s-1, and H2LD 2.7 × 10-5 cm2V-1s-1. We fabricated PSCs with these HTMs and among them the CuLD based PSCs showed highest power conversion efficiency of 12.44%. The better PCE for the PSCs fabricated with CuLD could be attributed to the higher conductivity and better hole mobility which could be correlated to the better film formation.

Performance research of perovskite solar cell with light conversion electron transport layer utilizing prism scattered lights

TiO2 conversion luminescent materials doped with Er3+ and Yb3+ are used as electron transport layer to enhance photoelectric performance of CH3NH3PbI3 perovskite solar cells (MAPbI3 PSC) under scattered solar light irradiation by prism. The composition, morphology and optical property of the films were characterized by XRD, XPS, SEM, UV–vis and PL. The up-conversion TiO2 luminescent film absorbs multiple low energy infrared photons and converts them into one visible photon, while the down-conversion TiO2 luminescent film absorbs one high-energy ultraviolet photon and converts it into multiple visible photons. The obtained visible photons can effectively excite the MAPbI3 perovskite to produce more photo-generated electron-hole pairs, thus improving the incident light utilization and power conversion efficiency (PCE) of MAPbI3 PSC. The MAPbI3 PSC with up-conversion TiO2, TiO2 and down-conversion TiO2 electron transport layer (UTD-MAPbI3 PSC) can effectively utilize the infrared, visible and ultraviolet lights obtained from the sunlight dispersed by a prism, respectively. Under the scattered solar light irradiation, the PCE of UTD-MAPbI3 PSC is increased by 11.22%, compared with that of the MAPbI3 PSC with un-doped TiO2 as the electron transport layer (TiO2-MAPbI3 PSC). This may provide a new idea to enhance the utilization ratio of sunlight for solar cells.

Syntheses of efficient nickel oxide film by low-temperature fabrication technique for high-performance perovskite solar cells

Interface modification is an effective technique to improve power conversion efficiency (PCE) of perovskite solar cells (PSCs). In this study, three kinds of hole transport layers (HTLs), including planar-nickel oxide (P-NiOx) film, surface-nanostructured-NiOx (S-NiOx) film, and modified-NiOx (M-NiOx) film, are synthesized by low-temperature fabrication technique. Furthermore, M-NiOx film is defined by modifying P-NiOx film with ultra-low concentration NiOx nanoparticles. The results show that the M-NiOx film has higher conductivity and carrier transport ability than those of P-NiOx and S-NiOx. The special morphology of M-NiOx film is beneficial to improving the crystallinity of MAPbI3 perovskite film. Thus, the PSC based on M-NiOx film exhibits the highest short-circuit current density (Jsc) of 21.30 mA cm−2, which is larger than those of PSCs based on P-NiOx (17.74 mA cm−2) and S-NiOx films (16.56 mA cm−2). The optimized PSC based on M-NiOx film exhibits the high photovoltaic performance with PCE of 16.67%. The optimized PSC with M-NiOx film shows a long-term stability. After storing in a nitrogen-filled glove box for 1000 h, the PSC with M-NiOx film still has 85% of its initial PCE.