Organic Solar Cell With Efficiency Over 20% and VOC Exceeding 2.1 V Enabled by Tandem With All-Inorganic Perovskite and Thermal Annealing-Free Process

Synergistic Optimization of n-i-p Structured Monolithic All-Inorganic Perovskite/Organic Tandem Solar Cells Achieving Efficiency over 24

CsPbI2Br-based perovskite solar cells (PSCs) garner significant attention in recent years due to their superior thermal stability compared to the organic-inorganic hybrid counterparts. Besides, with a bandgap of 1.92 eV making CsPbI2Br ideal candidates for combining with organic semiconductors to construct perovskite/organic tandem solar cells (TSCs), which achieve complementary absorption and high power conversion efficiency (PCE). However, the severe voltage loss at the interconnection layer (ICL) and unbalanced current of the subcells restrict the efficiency improvement of perovskite/organic TSCs. Herein, n-i-p structured monolithic all-inorganic perovskite/organic TSC is constructed with structure of ITO/Cl@MZO/CsPbI2Br/PM6/MoO3/Ag/PFN-Br/PM6:BTP-BO-4Cl:PC71BM/MoO3 /Ag. The thickness of the CsPbI2Br layer in the front subcell and the ratio of PM6:BTP-BO-4Cl:PC71 BM in the rear subcell are optimized to simultaneously achieve higher Jsc. Instead of unstable Spiro-OMeTAD, PM6 is employed as the hole transport material (HTM), and the ICL is fine-tuned to ensure a high fill factor (FF) and small open-circuit voltage (Voc) loss in the TSC. As a result, a remarkable PCE of 24.10%, along with a high Jsc of 13.90 mA cm-2 and an FF of 80.97% are achieved, among the best performance for CsPbI2Br-based n-i-p structured TSCs. Furthermore, the TSC exhibits outstanding stability under atmospheric conditions.

Mobile Oxygen Capture Enhances Photothermal Stability of Perovskite Solar Cells Under ISOS Protocols

Stability testing protocols from the International Summit on Organic and Hybrid Solar Cell Stability (ISOS) are essential for standardizing studies on the photothermally operational stability of perovskite solar cells (PSCs). Under photothermal conditions, the migration of oxygen from SnO2 layer induces cationic dehydrogenation at the A-site of the perovskite, accelerating degradation to PbI2. This leads to the formation of photoinduced I2 and Pb0 defects, significantly compromising long-term stability. In this study, ordonezite (ZnSb2O6-x) as a multifunctional electron transport layer (ETL) that captures migrating oxygen atoms at the SnO2/perovskite interface is introduced, effectively preventing degradation of the buried interface. Additionally, the lattice match between ZnSb2O6-x and perovskite facilitates well-ordered perovskite film growth. As a result, PSCs featuring ZnSb2O6-x ETLs achieved a high power conversion efficiency of 25.02% and retained 90.62% of their initial performance after 1000 h under the ISOS-D-2 protocol. Furthermore, devices demonstrated remarkable thermal stability, maintaining 83.69% of their original performance after 800 h of maximum power point tracking at 85 °C, meeting the stringent ISOS-L-2 protocol requirements.

High-Performance and Stable Perovskite/Organic Tandem Solar Cells Enabled by Interconnecting Layer Engineering

Perovskite/organic tandem solar cells (PO-TSCs) have recently attracted increasing attention due to their high efficiency and excellent stability. The interconnecting layer (ICL) is of great importance for the performance of PO-TSCs. The charge transport layer (CTL) and the charge recombination layer (CRL) that form the ICL should be carefully designed to enhance charge carrier extraction and promote charge carrier recombination balance from the two subcells. Here, we propose an effective strategy to optimize the ICL by using [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) to modify the poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) as the hole transport layer (HTL) in the ICL. It is found that the coverage state of 2PACz on the PEDOT:PSS significantly affects the performance of PO-TSCs and can be regulated by adjusting the concentration of the 2PACz solution. The PEDOT:PSS/2PACz structure facilitates effective charge carrier extraction from the organic solar cells to the CRL. Herein, for the PO-TSCs, this strategy results in an efficient and balanced charge carrier recombination in the ICL and also allows a thinner PEDOT:PSS with reduced parasitic absorption. As a result, the PO-TSC achieves a power conversion efficiency (PCE) of 25.26%, much higher than the control device (PCE of 23.57%), and better stability. This work demonstrates an effective approach to achieving high-performance PO-TSCs through ICL engineering.

Overcoming optical losses in thin metal-based recombination layers for efficient n-i-p perovskite-organic tandem solar cells

Perovskite-organic tandem solar cells (P-O-TSCs) hold substantial potential to surpass the theoretical efficiency limits of single-junction solar cells. However, their performance is hampered by non-ideal interconnection layers (ICLs). Especially in n-i-p configurations, the incorporation of metal nanoparticles negatively introduces serious parasitic absorption, which alleviates photon utilization in organic rear cell and decisively constrains the maximum photocurrent matching with front cell. Here, we demonstrate an efficient strategy to mitigate optical losses in Au-embedded ICLs by tailoring the shape and size distribution of Au nanoparticles via manipulating the underlying surface property. Achieving fewer, smaller, and more uniformly spherical Au nanoparticles significantly minimizes localized surface plasmon resonance absorption, while maintaining efficient electron-hole recombination within ICLs. Consequently, optimized P-O-TSCs combining CsPbI2Br with various organic cells benefit from a substantial current gain of >1.5 mA/cm2 in organic rear cells, achieving a champion efficiency of 25.34%. Meanwhile, optimized ICLs contribute to improved long-term device stability.

The Perovskite Optoelectronic Devices - A Look at the Future

The perovskite materials are broadly incorporated into optoelectronic devices due to a number of advantages. Their rapid technological progress is related to the relatively simple fabrication process, low production cost and high efficiency. Significant improvement is made in the light emitting, detection performance and device design especially operating in the visible and near-infrared regions. This review presents the status and possible future development of the perovskite devices such as solar cells, photodetectors, and light-emitting diodes. The fundamental properties of perovskite materials related to their effective device applications are summarized. Since the development of the perovskite technology is mainly driven by the revolutionary evolution of the semiconductor perovskite solar cell as a robust candidate for next-generation solar energy harvesting, this topic is considered first. The device engineering of various perovskite photodetector structures, including perovskite quantum dot photodetectors, is then discussed in detail. Their performance is compared with the current commercial photodetectors available on the global market together with their challenges. Finally, the considerable progress in the fabrication of the perovskite light-emitting diodes with external quantum efficiency exceeding 20% is presented. The paper is completed in an attempt to determine the development of perovskite optoelectronic devices in the future.

Small molecular donor materials based on β-β-bridged BODIPY dimers with a triphenylamine or carbazole unit for efficient organic solar cells

Herein, we have designed and synthesized two novel BODIPY dimer-based small molecules, denoted as ZMH-1 and ZMH-2, covalently linked and functionalized with triphenylamine (TPA) (ZMH-1) and carbazole (CZ) (ZMH-2) units as the electron donor at the 3- and 5-positions of the BODIPY core, respectively. Their optical and electrochemical properties were investigated. We have fabricated all small molecule bulk heterojunction organic solar cells using these BODIPY-based small molecules as electron donors along with fullerene derivative (PC71BM) and medium bandgap non-fullerene acceptor IDT-TC as electron acceptors. The optimized OSCs based on ZMH-1:PC71BM, ZMH-2:PC71BM, ZMH-1:IDT-IC, and ZMH-2:IDT-IC attain overall PCEs of 8.91%, 6.61%, 11.28%, and 5.48%, respectively. Moreover, when a small amount of PC71BM as guest acceptor is added to the binary host ZMH-1:IDT-TC and ZMH-2:IDT-TC, the ternary OSCs based on ZMH-1 and ZMH-2 reach PCEs of 13.70% and 12.71%, respectively.

Engineering of the Central Core on DBD-Based Materials with Improved Power-Conversion Efficiency by Using the DFT Approach

Developing proficient organic solar cells with improved optoelectronic properties is still a matter of concern. In the current study, with an aspiration to boost the optoelectronic properties and proficiency of organic solar cells, seven new small-molecule acceptors (Db1-Db7) are presented by altering the central core of the reference molecule (DBD-4F). The optoelectronic aspects of DBD-4F and Db1-Db7 molecules were explored using the density functional theory (DFT) approach, and solvent-state calculations were assessed utilizing TD-SCF simulations. It was noted that improvement in photovoltaic features was achieved by designing these molecules. The results revealed a bathochromic shift in absorption maxima (λmax) of designed molecules reaching up to 776 nm compared to 736 nm of DBD-4F. Similarly, a narrow band gap, low excitation energy, and reduced binding energy were also observed in newly developed molecules in comparison with the pre-existing DBD-4F molecule. Performance improvement can be indicated by the high light-harvesting efficiency (LHE) of designed molecules (ranging from 0.9992 to 0.9996 eV) compared to the reference having a 0.9991 eV LHE. Db4 and Db5 exhibited surprisingly improved open-circuit voltage (V OC) values up to 1.64 and 1.67 eV and a fill factor of 0.9198 and 0.9210, respectively. Consequently, these newly designed molecules can be considered in the future for practical use in manufacturing OSCs with improved optoelectronic and photovoltaic attributes.

Opportunities and challenges in perovskite-organic thin-film tandem solar cells

Efficiency is paramount in enhancing the performance and cost-effectiveness of solar cells. Recent advancements in single-junction perovskite solar cells (PSCs) have yielded an impressive efficiency of 26.1%, nearing their theoretical limit. Meanwhile, multi-junction tandem solar cells exhibit a remarkable efficiency potential exceeding 42%, surpassing the 33% limit of single-junction cells, thereby opening avenues for ultra-high-efficiency solar cells. Tandem solar cells (TSCs) represent a groundbreaking photovoltaic technology, offering high efficiency, low cost, and a simple fabrication process. Among various TSCs, perovskite-organic TSCs (PO TSCs) are particularly promising due to their ability to leverage the complementary strengths of PSCs and organic solar cells (OSCs). PO TSCs are poised to outperform existing TSCs in terms of device performance, manufacturing cost, and diverse applications. The introduction of Y6-series non-fullerene acceptors (NFAs) over the past three years has significantly advanced the development of OSCs, leading to remarkable progress in PO TSCs. This paper commences by elucidating the advantages and potential of OSCs as bottom sub-cells in PO TSCs, followed by an in-depth review of mainstream interconnection layer (ICL) design. It then addresses key challenges in wide bandgap PSCs, including phase segregation, photovoltage loss, energy loss, and long-term stability. The paper concludes by examining critical factors influencing the future development of PO TSCs.

Antisolvent-Free Heterogenous Nucleation Enabled by Employing 4-Tert-Butyl Pyridine Additive and Two-Step Annealing for Efficient CsPbI2Br Perovskite Solar Cells

All inorganic perovskite based on CsPbI2Br has attracted significant attention due to its relatively thermal stable structure compare to its hybrid counterparts. With a wide bandgap of 1.9 eV and excellent light absorption capability, it has been extensively explored for applications in indoor photovoltaics and as a front absorber in tandem devices. However, the uncontrollable crystallization process during solvent evaporation and thermal annealing leads to both macroscopic defects like cracks and microscopic defects such as voids. In this study, a metastable adduct with lead (II) halides by incorporating 4-tert-butyl pyridine as a volatile Lewis base monodentate ligand in the precursor solution is formed. The strategic preferential decomposition of the adduct during the early-stage low-temperature annealing facilitated the desorption of lead (II) halides, inducing antisolvent-free heterogenous nucleation. This, in turn, promoted crystal growth during subsequent high-temperature annealing, resulting in dense films with low defect density. As a result, a maximum open-circuit voltage of 1.30 V is achieved with the champion power conversion efficiency of 16.5% in CsPbI2Br-based perovskite solar cell. The work reveals a new mechanism of using Lewis acid-base adduct to obtain high quality perovskite films other than hindering crystallization in traditional way.

Interface Engineering for Highly Efficient Organic Solar Cells

Organic solar cells (OSCs) have made dramatic advancements during the past decades owing to the innovative material design and device structure optimization, with power conversion efficiencies surpassing 19% and 20% for single-junction and tandem devices, respectively. Interface engineering, by modifying interface properties between different layers for OSCs, has become a vital part to promote the device efficiency. It is essential to elucidate the intrinsic working mechanism of interface layers, as well as the related physical and chemical processes that manipulate device performance and long-term stability. In this article, the advances in interface engineering aimed to pursue high-performance OSCs are reviewed. The specific functions and corresponding design principles of interface layers are summarized first. Then, the anode interface layer, cathode interface layer in single-junction OSCs, and interconnecting layer of tandem devices are discussed in separate categories, and the interface engineering-related improvements on device efficiency and stability are analyzed. Finally, the challenges and prospects associated with application of interface engineering are discussed with the emphasis on large-area, high-performance, and low-cost device manufacturing.

Advances in Hole Transport Materials for Layered Casting Solar Cells

Huge energy consumption and running out of fossil fuels has led to the advancement of renewable sources of power, including solar, wind, and tide. Among them, solar cells have been well developed with the significant achievement of silicon solar panels, which are popularly used as windows, rooftops, public lights, etc. In order to advance the application of solar cells, a flexible type is highly required, such as layered casting solar cells (LCSCs). Organic solar cells (OSCs), perovskite solar cells (PSCs), or dye-sensitive solar cells (DSSCs) are promising LCSCs for broadening the application of solar energy to many types of surfaces. LCSCs would be cost-effective, enable large-scale production, are highly efficient, and stable. Each layer of an LCSC is important for building the complete structure of a solar cell. Within the cell structure (active material, charge carrier transport layer, electrodes), hole transport layers (HTLs) play an important role in transporting holes to the anode. Recently, diverse HTLs from inorganic, organic, and organometallic materials have emerged to have a great impact on the stability, lifetime, and performance of OSC, PSC, or DSSC devices. This review summarizes the recent advances in the development of inorganic, organic, and organometallic HTLs for solar cells. Perspectives and challenges for HTL development and improvement are also highlighted.

Study of Tunable Dielectric Permittivity of PBDB-T-2CL Polymer in Ternary Organic Blend Thin Films Using Spectroscopic Ellipsometry

The ellipsometric analyses reported in this paper present a novelty by bringing an in-depth optical investigation of some ternary organic blends. This study focuses on the tunability and control of the relative permittivity of active layers by varying the weight ratio of blended materials spin-coated as thin films. To investigate this, an extensive approach based on spectroscopic ellipsometry was conducted on ternary blend (D:A1:A2) thin films, involving a donor [D = chlorinated conjugated polymer (PBDB-T-2Cl)] and two acceptor materials [A1 = a non-fullerene (ITIC-F) and A2 = a fullerene (PCBM)]. The refractive index constitutes a key parameter that exposes insights into the feasibility of photovoltaic cells by predicting the trajectory of light as it transits the device. In this term, higher obtained refractive indexes support higher absorption coefficients. Notably, the dielectric constant can be rigorously tuned and finely calibrated by modest variations in the quantity of the third element, resulting in considerable modifications. Moreover, the inclusion of fullerene in blends, as the third element, results in a smooth topographical profile, further refining the surface of the film. From an electrical point of view, the ternary blends outperform the polymer thin films. The synergistic interaction of constituents emphasizes their potential to enhance solar conversion devices.

Influence of Component Properties on the Photovoltaic Performance of Monolithic Perovskite/Organic Tandem Solar Cells: Sub-Cell, Interconnecting Layer, and Photovoltaic Parameters

Wide-bandgap perovskite sub-cells (WPSCs)-based tandem solar cells attract considerable interest because of their capability to surpass the Shockley-Queisser limit. Monolithic perovskite/organic tandem solar cells (POTSCs) integrating WPSCs and small-bandgap organic sub-cells (SOSCs) are famous compositions owing to their simple fabrication method and compatibility with flexible devices. Most studies on POTSCs focus on enhancing device efficiency by modifying one or two of the device components (WPSCs, SOSCs, and interconnecting layers). The characteristics of POTSCs are not extensively investigated so far, especially in terms of the influence of the device structure and component properties on the tandem device photovoltaic performance. In this study, the existing p-i-n type WPSC-based p-i-n POTSCs and n-i-p type WPSC-based n-i-p POTSCs are reviewed and their advantages and limitations are highlighted. Furthermore, the influence of the tandem device component properties (optical, electrical, and photovoltaic properties) on the photovoltaic parameters (open-circuit voltage, short-circuit current density, fill factor, and power conversion efficiency) and the existing device modification methods are discussed to provide comprehensive guidance for the development of POTSCs.

Recent Advances in Wide-Bandgap Organic-Inorganic Halide Perovskite Solar Cells and Tandem Application

Perovskite-based tandem solar cells have attracted increasing interest because of its great potential to surpass the Shockley-Queisser limit set for single-junction solar cells. In the tandem architectures, the wide-bandgap (WBG) perovskites act as the front absorber to offer higher open-circuit voltage (VOC) for reduced thermalization losses. Taking advantage of tunable bandgap of the perovskite materials, the WBG perovskites can be easily obtained by substituting halide iodine with bromine, and substituting organic ions FA and MA with Cs. To date, the most concerned issues for the WBG perovskite solar cells (PSCs) are huge VOC deficit and severe photo-induced phase separation. Reducing VOC loss and improving photostability of the WBG PSCs are crucial for further efficiency breakthrough. Recently, scientists have made great efforts to overcome these key issues with tremendous progresses. In this review, we first summarize the recent progress of WBG perovskites from the aspects of compositions, additives, charge transport layers, interfaces and preparation methods. The key factors affecting efficiency and stability are then carefully discussed, which would provide decent guidance to develop highly efficient and stable WBG PSCs for tandem application.

Regulating Charge Carrier Recombination in the Interconnecting Layer to Boost the Efficiency and Stability of Monolithic Perovskite/Organic Tandem Solar Cells

The charge carriers of single-junction solar cells can be fluently extracted and then collected by electrodes, leading to weak charge carrier accumulation and low energy loss (E_loss ). However, in tandem solar cells (TSCs), it is a considerable challenge to obtain a balance between the densities of the holes and electrons extracted from the two respective subcells to facilitate an efficient recombination in the interconnecting layer (ICL). Herein, a charge-carrier-dynamic management strategy for inorganic perovskite/organic TSCs is proposed, centered on the simultaneous regulation of the defect states of CsPbI_1.9 Br_1.1 perovskite in the front subcell and hole transport ability from the perovskite to ICL. The target hole density on the perovskite surface and the hole loss before reaching the ICL are significantly improved. As a result, the hole/electron density offset in the ICL can be effectively narrowed, leading to a balanced charge carrier recombination, which reduces the E_loss in TSCs. The resulting inorganic perovskite/organic 0.062-cm² TSC exhibits a remarkable power conversion efficiency (PCE) of 23.17% with an ultrahigh open-circuit voltage (V_oc ) of 2.15 V, and the PCE of the 1.004-cm² device (21.69%) exhibited a weak size-dependence. This charge-carrier-dynamic management strategy can also effectively enhance the operational and ultraviolet-light stabilities of the TSCs.

4-Terminal Inorganic Perovskite/Organic Tandem Solar Cells Offer 22% Efficiency

After fast developing of single-junction perovskite solar cells and organic solar cells in the past 10 years, it is becoming harder and harder to improve their power conversion efficiencies. Tandem solar cells are receiving more and more attention because they have much higher theoretical efficiency than single-junction solar cells. Good device performance has been achieved for perovskite/silicon and perovskite/perovskite tandem solar cells, including 2-terminal and 4-terminal structures. However, very few studies have been done about 4-terminal inorganic perovskite/organic tandem solar cells. In this work, semi-transparent inorganic perovskite solar cells and organic solar cells are used to fabricate 4-terminal inorganic perovskite/organic tandem solar cells, achieving a power conversion efficiency of 21.25% for the tandem cells with spin-coated perovskite layer. By using drop-coating instead of spin-coating to make the inorganic perovskite films, 4-terminal tandem cells with an efficiency of 22.34% are made. The efficiency is higher than the reported 2-terminal and 4-terminal inorganic perovskite/organic tandem solar cells. In addition, equivalent 2-terminal tandem solar cells were fabricated by connecting the sub-cells in series. The stability of organic solar cells under continuous illumination is improved by using semi-transparent perovskite solar cells as filter.