Promote Carrier Transport Research Articles

Efficient and stable all-inorganic perovskite solar cells prepared with ABX3-like precursors

Despite the fact that inorganic perovskites with supreme thermal stability are attractive photo-absorbers for emerging photovoltaic cells, intrinsic phase-instable issues pose challenges for obtaining satisfactory photovoltaic efficiencies and long-term device stability. Herein, we demonstrate an all-solution approach based on a series of perovskite-like products (PLP), namely NH4PbX3 (X = halogen) as the reactant for preparing inorganic perovskites featuring a heterojunction-resembling structure (HRS) and high material robustness. The creation of HRS is enabled by a self-migration and assembly process facilitated by the volatile characteristics of PLPs, as affirmed by joint experiential and theoretical investigations. We highlight that the particular structure of HRS is a key to the boost in material robustness, which translates to long-term device stability. Engaging compositional engineering on the PLPs allows us to regulate the energetics of surface components within the HRS, leading to gradient energy alignments to promote carrier transport and extraction in the device. Based on an optimized PLP (NH4PbCl2.8Br0.2) to form the HRS, the resultant solar cell yields a power conversion efficiency (PCE) exceeding 20 %, showing excellent operational stability under illumination (the efficiency remains over 95 % of its initial value after 1000 hours of continuous illumination). The described PLP-based approach can be readily applied to a range of inorganic perovskite materials for receiving gains in photovoltaic performance.

Multifunctional Ammonium Sulfide Enables Highest Efficiency Lead–Tin Perovskite Solar Cells

AbstractThe commonly used hole transport layer (HTL) Poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) still has some shortcomings that will limit the development of Pb–Sn perovskite solar cells (PSCs). In this work, multifunctional ammonium sulfide (AS) is attempted to modify PEDOT:PSS/perovskite interface. AS has multiple effects on different functional layers and the device as a whole: a) optimize the perovskite crystallization by the formation of PbS nucleation sites; b) neutralize the acidity of PEDOT:PSS by reaction with PSS; c) promote carrier transport at HTL/perovskite interface by tuning the energy level of PEDOT:PSS. As a result, a power conversion efficiency of 24.23% is obtained in the reverse scanning direction and 23.84% in the steady‐state output power test for the single‐junction Pb–Sn PSCs, and 27.48% for all‐perovskite tandem solar cells. These results show that AS modification can be an effective way to boost the development of Pb–Sn PSCs.

Promoting energy transfer via manipulation of crystallization kinetics of quasi-2D Dion–Jacobson phase perovskites for high-performance green lasers

The quasi-2D Dion–Jacobson perovskite exhibits significant photophysical properties and potential applications. However, the insufficient exciton energy transfer leads to nonradiative recombination that seriously hinders charge transport. Here, an efficient energy transfer is achieved by incorporating the alkali metal, which not only constrains the nucleation of high-n phases and promotes the growth of the middle-n phases but also optimizes the phase distribution and the crystal orientation to promote carrier transport. We achieve a green amplified spontaneous emission with a low threshold of 28.5 μJ/cm2 and a vertical-cavity laser operating in a single-mode configuration with a linewidth of 0.96 nm.

Effects of 3-Bromo-N-methylbenzylamine modification on CsPbI2Br perovskite films and perovskite solar cells

In this work, 3-Bromo-N-methylbenzylamine (3-B-N-MB) was designed to modify CsPbI2Br/hole transport layer interface to reduce the interfacial non-radiative recombination loss of all-inorganic CsPbI2Br perovskite solar cells (PSCs). The effects of 3-B-N-MB modification on the morphology, structure, optical absorption, defect concentration, carrier lifetime, energy level, hydrophobicity of CsPbI2Br perovskite film and device performance, and carrier dynamics, as well as their mechanisms were systematically studied. The results show that the lone pair electrons in the N atom of N-H group in strongly alkaline 3-B-N-MB is more conducive to coordinate with uncoordinated Pb2+/Cs+ in CsPbI2Br, meanwhile the H atom of N-H group in 3-B-N-MB can react with I−/Br− in CsPbI2Br through hydrogen bonding, passivating interface defects to increase grain size and enhance the crystallinity and density of CsPbI2Br films, optimizing interface energy level matching to promote carrier transport, thus suppressing interfacial non-radiative recombination to improve device performance. As a result, the PCE of the 3-B-N-MB modified PSCs significantly enhanced ∼32.5 % as compared to that of the pristine one and the air stability of the device has also improved. The 3-B-N-MB modification provides a new strategy to enhance the efficiency and stability of all-inorganic perovskite solar cells.

Interfacial Coulomb-enhanced charge injection for efficient perovskite light-emitting diodes

Unbalanced electron-hole injection in perovskite light-emitting diodes (PeLEDs) has always been a major stumbling block limiting device performance. Here we develop a heterointerface Coulomb enhancement strategy to efficiently promote electron injection between perovskite emitter and transport layer and thereby balance the electron-hole recombination equilibrium through manipulating defect-rich positive-charge centers induced Coulomb interactions in LiF interlayer. Through multiscale polarization response characterizations combined with capacitance-voltage and electrochemical impedance spectroscopy, it is confirmed that diffusing holes trapped in LiF layer leads to the increased interfacial polarization. Moreover, the polarization response reversal and high-frequency-dependent dissipation sensitivity further corroborate the LiF-induced interfacial Coulomb enhancement mechanism. The universality of the concept is also successfully verified in devices with electron-only, hole-only, and PN structures. Consequently, the modified PeLEDs show a lower leakage current, along with a significant performance improvement by 1.9 times in external quantum efficiency (18.8%) and 5.7 times in luminance compared with control samples. This study provides a unique perspective to promote carrier transport balance by taking advantage of physical effects within interlayer.

The study of optical and electrical properties of AgInS2-based composite

sPhotovoltaic solar energy was one of the few sustainable and pollution-free energy sources. AgInS2 was a promising photovoltaic material, which had attracted considerable in long time due to its outstanding photovoltaic performance. Furthermore, the nanoparticles could improve the light absorption efficiency of absorption layer to enhance the photoelectric conversion efficiency of solar cell. In this paper, the suitable preparation methods of AgInS2 film and gold nanoparticles were used to improve the optical-electric performances of AgInS2-based solar cell. AgInS2 films were prepared by vacuum evaporation using different raw materials (Ag + In + S and Ag2S + In2S3) and then annealed at 400 °C or 425 °C. From absorption spectrum, the AgInS2 film, which was prepared by two components (Ag2S + In2S3) and annealed at 400 °C, had the highest absorption. And the transmission spectrum of the AgInS2 film was similar to that obtained from finite difference time domain simulation. Furthermore, this AgInS2 film was used to prepare AgInS2/CdS PN junction and AgInS2/gold/CdS PN junction. Due to the introduction of gold nanoparticles, the forward current of the AgInS2/gold/CdS PN junction increased an order of magnitude, but ideal factor and barrier height decreased, which meant that gold nanoparticles can promote carrier transport and improve electric property. As a result, this AgInS2/gold/CdS PN junction owned high absorption efficiency, low reverse saturation current and large barrier height, which meant huge application potential in solar cells field.

Element Diffusion Induced Carrier Transport Enhancement in High-Performance CZTSSe Self-Powered Photodetector.

Cu2ZnSn(S,Se)4 (CZTSSe) has attracted great interest in thin-film solar cells due to its excellent photoelectric performance in past decades, and recently is gradually expanding to the field of photodetectors. Here, the CZTSSe self-powered photodetector is prepared by using traditional photovoltaic device structure. Under zero bias, it exhibits the excellent performance with a maximum responsivity of 0.77 A W-1, a high detectivity of 8.78 × 1012 Jones, and a wide linear dynamic range of 103dB. Very fast response speed with the rise/decay times of 0.576/1.792 µs, and ultra-high switching ratio of 3.54 × 105 are obtained. Comprehensive electrical and microstructure characterizations confirm that element diffusion among ITO, CdS, and CZTSSe layers not only optimizes band alignment of CdS/CZTSSe, but also suppresses the formation of interface defects. Such a suppression of interface defects and spike-like band alignment significantly inhibit carrier nonradiative recombination at interface and promote carrier transport capability. The low trap density in CZTSSe and low back contact barrier of CZTSSe/Mo could be responsible for the very fast response time of photodetector. This work definitely provides guidance for designing a high performance self-powered photodetector with high photoresponse, high switching ratio, fast response speed, and broad linear dynamic range.

Covalent Organic Framework as a Precursor Additive Toward Efficient and Stable Perovskite Solar Cells

In recent years, there has been significant progress in the use of organic–inorganic hybrid perovskites for photovoltaic applications. Engineering the compositions and/or morphology of perovskites has become the most effective method to address the challenges related to photovoltaic efficiency and stability. Herein, an amino‐functionalized covalent organic framework (NH2‐COF) as a precursor additive to modulate the crystallization of perovskites is incorporated. The NH2‐COF is found to decrease the defect concentration, reduce the nonradiative recombination within the perovskite layer, and further promote carrier transport. Correspondingly, the solar cells based on the NH2‐COF‐modified perovskites deliver a champion power conversion efficiency of 22.13% with a fill factor of 0.773 under AM 1.5G 100 mW cm−2 illumination. Furthermore, the device retains approximately 81% of its initial efficiency after 1000 h of aging under ambient conditions at a temperature of 30 °C and relative humidity ranging from 45% to 55%. It is believed that this work would provide a facile and efficient strategy to prepare high‐quality perovskite films for efficient and stable solar cells.

RGO/CNTs/PEDOT: PSS ternary composites with enhanced thermoelectric properties

Graphene oxide/ carbon nanotubes (GO/CNTs) aerogels were prepared by adjusting the proportion of GO and CNTs, the corresponding reduced graphene oxide/CNTs (rGO/CNTs) aerogels were obtained by thermal reduction. Then, poly (3,4-ethylenedioxythiophene): polystyrene sulfonic acid (PEDOT: PSS) was compounded with rGO/CNTs aerogels at a mass ratio of 1:1 to prepare rGO/CNTs/PEDOT: PSS (GCP) composites. Structural analyses revealed the strong π-π interaction between rGO/CNTs and PEDOT: PSS, which leads to the formation of ordered regions. Porous structures of rGO/CNTs aerogels act as conductive network skeleton to promote carrier transport in GCP composites, and the electrical conductivity of GCP composites improves effectively. The optimal electrical conductivity and Seebeck coefficient of GCP5 were 1788.11 S cm−1 and 15.87 μV K−1 respectively. The maximum power factor and ZT merit of GCP5 achieved to 45.03 μW m−1 K−2 and 2.65 × 10−2 at room temperature, which was almost 43 and 17 times than that of PEDOT: PSS.

Carrier Mobility Modulation in Cu2Se Composites Using Coherent Cu4TiSe4 Inclusions Leads to Enhanced Thermoelectric Performance

Carrier transport engineering in bulk semiconductors using inclusion phases often results in the deterioration of carrier mobility (μ) owing to enhanced carrier scattering at phase boundaries. Here, we show by leveraging the temperature-induced structural transition between the α-Cu2Se and β-Cu2Se polymorphs that the incorporation of Cu4TiSe4 inclusions within the Cu2Se matrix results in a gradual large drop in the carrier mobility at temperatures below 400 K (α-Cu2Se), whereas the carrier mobility remains unchanged at higher temperatures, where the β-Cu2Se polymorph dominates. The sharp discrepancy in the electronic transport within the α-Cu2Se and β-Cu2Se matrices is associated with the formation of incoherent α-Cu2Se/Cu4TiSe4 interfaces, owing to the difference in their atomic structures and lattice parameters, which results in enhanced carrier scattering. In contrast, the similarity of the Se sublattices between β-Cu2Se and Cu4TiSe4 gives rise to coherent phase boundaries and good band alignment, which promote carrier transport across the interfaces. Interestingly, the different cation arrangements in Cu4TiSe4 and β-Cu2Se contribute to enhanced phonon scattering at the interfaces, which leads to a reduction in the lattice thermal conductivity. The large reduction in the total thermal conductivity while preserving the high power factor of β-Cu2Se in the (1-x)Cu2Se/(x)Cu4TiSe4 composites results in an improved ZT of 1.2 at 850 K, with an average ZT of 0.84 (500-850 K) for the composite with x = 0.01. This work highlights the importance of structural similarity between the matrix and inclusions when designing thermoelectric materials with improved energy conversion efficiency.

Construction of a Highly Anisotropic Supramolecular Assembly Assisted by a Dimensional Confinement Space: Toward Perovskite Solar Cells.

Solution-processed polycrystalline perovskites (PVKs) have aroused tremendous interest in the optoelectronic device field. However, the inherent high-density defects in the polycrystalline hindered achieving efficient and stable large-area PVK solar cells (PSCs). Although organic molecules are already employed to passivate PVK defects, they are insulating by nature, limiting the carrier transport. Here, we design an assembly of a small molecule (N,N'-di(propanoic acid)-perylene-3,4,9,10-tetracarboxylic diamide, PDI) via confinement-assisted supramolecular polymerization technology, which is used as a binder for grain boundaries to simultaneously passivate defects and promote carrier transport. The synergistic effect allows the efficiency of all-air processed carbon-based PSCs to reach a decent power conversion efficiency of 14.17%. Importantly, the as-prepared supramolecular assembly completely breaks through the insulating nature of the single molecule, which exists in the long-term defect passivation of PSCs by organic molecules. It is expected that this finding may provide novel design ideas to apply the assemblies to improve the performance of PSCs.

Dual‐Site Synergistic Passivation for Highly Efficient and Stable Perovskite Solar Cells

AbstractDefect passivation has been recognized as an effective strategy to improve efficiency and stability of perovskite solar cells (PSCs). In this work, in‐depth theoretical calculations and experimental characterizations reveal the dual‐site synergistic passivation of 1H‐benzimidazole (BIZ), and the conjugated structure of the benzene ring tends to increase the interaction between BIZ and perovskite. High‐quality perovskite films are thus achieved, with increased grain size, reduced defect density, and suppressed ion migration. Simultaneously, the reduced work function and optimized band alignment promote carrier transport, reducing nonradiative recombination, and loss of open‐circuit voltages, as well as fill factor. Consequently, the target PSC devices achieve a champion power conversion efficiency (PCE) of 24.59%, and 20.49% for perovskite solar module (a designated area of 27.5 cm2). The unencapsulated PSC maintains 91.49% of original PCE after storing in air with an average relative humidity of 40% for 2400 h. Moreover, the device exhibits remarkable the long‐term operational stability, maintaining 90.47% of initial PCE after continuously operating at the maximum power point for 1000 h. This study not only provides insights into the synergistic passivation of BIZ but also provides a strategy for the application of BIZ derivatives in the photovoltaic field.

CsPbBr3 seeds improve crystallization and energy level alignment for highly efficient CsPbI3 perovskite solar cells

CsPbI3 perovskite solar cells (PSCs) are becoming desirable for their outstanding performance and thermal stability, while their inferior tolerance to moisture restricts further advances. Herein, CsPbBr3 pieces are introduced onto TiO2 electron transport layer (ETL) before CsPbI3 film deposition, which can act as nucleation seeds to assist crystal growth and decrease the trap defects. Meanwhile, we reveal that bromide ions in CsPbBr3 seeds can diffuse toward atop CsPbI3 film to improve energy level alignment and promote carrier transport after annealing process. In this way, the simultaneous crystal growth regulation and interface engineering are triggered in CsPbI3 PSC by CsPbBr3 seeds. Therefore, a remarkable efficiency of 18.60 % was achieved for the optimized CsPbI3 PSC, and it can maintain 86 % of its initial efficiency after being stored for 500 h in ambient environment with controlled relative humidity (RH) of 10–20 %. Our work demonstrates an interesting method to fabricate high-performance CsPbI3 PSCs to promote their potential commercialization.

Directly integrated mixed‐dimensional van der Waals graphene/perovskite heterojunction for fast photodetection

AbstractMixed‐dimensional (2D/3D) van der Waals (vdW) heterostructures made with complementary materials hold a lot of promise in the field of optoelectronic devices. Beyond simple mechanical stacking, directly growing the single‐crystal perovskite on 2D materials to construct a high‐quality vdW heterojunction can better promote carrier transport. In this work, a monolithic integrated graphene/perovskite heterojunction device is fabricated by directly growing a single‐crystal hybrid perovskite on monolayer graphene. Due to the strong interface coupling, the hybrid device achieves self‐powering behavior and exhibits prominent photoresponse properties with a fast response speed of up to 2.05 μs. Moreover, the responsivity and detectivity can be boosted to up to 10.41 A W−1 and 4.65 × 1012 Jones under the actuation of −3 V bias. This technique not only improves the device performance, but also provides an effective guideline for the development of next‐generation directly integrated vdW optoelectronic devices. image

Effects of Adding Alkali Metals and Organic Cations to Cu-Based Perovskite Solar Cells

First-principles electronic band calculations were used to investigate the effects of alkali metals and organic cations added to Cu-based perovskite solar cells. The copper d-orbital band was slightly above the valence-band maximum and functioned as an acceptor level for carrier generation. Excitation from iodine p-orbitals and copper d-orbitals to alkali metal s-orbitals could suppress carrier recombination and promote carrier transport. Experimental solar conversion efficiencies increased after adding both Cu and Na, in agreement with the calculations. Total-energy calculations indicated that the perovskite crystal stability increased with the addition of ethyl ammonium, although the total energy decreased with the addition of Cu and Na.

Research progress of nanoarray structure transport layers in perovskite solar cells

The electron/hole transport layer can promote charge transfer and improve device performance, which is used in perovskite solar cells. The nanoarray structure transport layers can not only further promote carrier transport but also reduce recombination. It also has a great potential in enhancing perovskite light absorption, improving device stability and inhibiting the crack nucleation of different structure layers in perovskite solar cells. This paper reviewed the research progress of perovskite solar cells with different nanoarray structure transport layers. The challenges and development directions of perovskite solar cells based on nanoarray structure transport layers are also summarized and prospected.

Controllable Distribution of Oxygen Vacancies in Grain Boundaries of p‐Si/TiO2 Heterojunction Photocathodes for Solar Water Splitting

AbstractSilicon is a promising photocathode material in photoelectrochemical water splitting for hydrogen production, but it is primarily limited by photocorrosion in aqueous electrolytes. As an extensively used protective material, crystalline TiO2 could protect Si photoelectrode against corrosion. However, a large number of grain boundaries (GBs) in polycrystalline TiO2 would induce excessive recombination centers, impeding the carrier transport. This paper describes the introduction of oxygen vacancies (Ovac) with controllable spatial distribution for GBs to promote carrier transport. Two kinds of Ovac distribution, Ovac along GBs and Ovac inside grains, are compared, where the latter one is demonstrated to facilitate carrier transport owing to the formation of tunneling paths across GBs. Consequently, a simple p‐Si/TiO2/Pt heterojunction photocathode with controllable Ovac distribution in TiO2 shows a +400 mV onset potential shift and yields an applied bias photon‐to‐current efficiency of 5.9 %, which is the best efficiency reported among silicon photocathodes except for silicon homojunction.

Controllable Distribution of Oxygen Vacancies in Grain Boundaries of p-Si/TiO2 Heterojunction Photocathodes for Solar Water Splitting.

Silicon is a promising photocathode material in photoelectrochemical water splitting for hydrogen production, but it is primarily limited by photocorrosion in aqueous electrolytes. As an extensively used protective material, crystalline TiO2 could protect Si photoelectrode against corrosion. However, a large number of grain boundaries (GBs) in polycrystalline TiO2 would induce excessive recombination centers, impeding the carrier transport. This paper describes the introduction of oxygen vacancies (Ovac ) with controllable spatial distribution for GBs to promote carrier transport. Two kinds of Ovac distribution, Ovac along GBs and Ovac inside grains, are compared, where the latter one is demonstrated to facilitate carrier transport owing to the formation of tunneling paths across GBs. Consequently, a simple p-Si/TiO2 /Pt heterojunction photocathode with controllable Ovac distribution in TiO2 shows a +400 mV onset potential shift and yields an applied bias photon-to-current efficiency of 5.9 %, which is the best efficiency reported among silicon photocathodes except for silicon homojunction.

A series of porphyrins as interfacial materials for inverted perovskite solar cells

Abstract Interface materials can improve the photovoltaic performance of the hybrid organic-inorganic perovskite solar cells (PSCs). Here, a series of porphyrin derivatives (metalloporphyrins: MTPPS4, M = Zn2+, Cu2+, Co2+, Ni2+; free base porphyrin: TPPS4) were developed to act as interfacial materials in PSCs. The introduction of porphyrin interlayers between PEDOT:PSS and perovskite layer in the inverted PSCs not only made energy level more matching but also improved the quality of the perovskite layer. Compared with the control device without an interlayer, the maximum power conversion efficiencies (PCE) of devices with the interlayers (in the order of ZnTPP4, CuTPP4, CoTPP4, NiTPP4 and TPP4) were increased by 23%, 25%, 21%, 17% and 13%, respectively. The highest PCE of 14.61% was based on the CuTPPS4-modified device. The porphyrins acted as the interlayers to promote carrier transport and reduce charge recombination at the interface, resulting in the increase of open-circuit voltage (VOC), short-circuit current density (JSC) and fill factor (FF).

The role of front-surface charges in interdigitated back contact silicon heterojunction solar cells

Silicon (Si) heterojunction (HJ) solar cells (SCs) with interdigitated back contacts (IBCs) have drawn increasing attention due to their high efficiencies. Top surface passivation on this type of SCs is extremely important because of the need for the photogenerated carriers to be collected by the rear electrodes with minimal losses. Here, we propose that the built-in fixed charges in the front side dielectric passivation thin film (DPTF) can ideally provide excellent field-effect passivation suitable for high efficiency IBC SCs. The photoelectric mechanisms due to the polarity and density (Qf up to ±1013 cm−2) of the front side fixed charges, and interface defect density (Dit up to 1012 eV−1cm−2), as well as their overall effects on cell efficiency, were investigated via numerical simulations. It was revealed that the front-surface charges effectively promote carrier transport inside the bulk Si and suppress recombination losses at the hole transport layer/c-Si, electron transport layer/c-Si and rear gap/c-Si interfaces. Once the condition |Qf| > 5 × 1012 cm−2 is met, irrespective of the surface charge polarity, an efficiency greater than 22% can be achieved with high tolerance to interface defects. On the other hand, the negative polarity of Qf will yield superior performance only in cases of moderate or poor quality passivation of the rear interfaces, and for thinner c-Si SCs. We believe that our results provide significant guidance for the screening of dielectric passivation materials in the development of high efficiency IBC-HJ SCs.