Electrochemical impedance spectroscopy of a novel ZnA–CA (Zinc Acetate–Citric acid) supramolecular metallogel

Recent advances in the application of two-dimensional materials as charge transport layers in organic and perovskite solar cells

As organic solar cells (OSCs) and perovskite solar cells (PVSCs) move closer to commercialization, further efforts toward optimizing both cell efficiency and stability are needed. As interfaces strongly affect device performance and degradation processes, interfacial engineering by employing various materials as hole transport layers (HTLs) and electron transport layers (ETLs) has been a very active field of research in OSCs and PVSCs. Among them, inorganic materials exhibit significant advantages in promoting device performance due to their excellent charge transporting properties and intrinsic thermal and chemical robustness. In this review, an extensive overview is provided of inorganic semiconductors such as copper‐based ones with emphasis on copper iodide and copper thiocyanate, transition metal chalcogenides, nitrides and carbides as well as hybrid materials based on these inorganic compounds that have been recently employed as HTLs and ETLs in OSCs and PVSCs. Following a short discussion of the main optoelectronic and physical properties that interfacial materials used as HTLs and ETLs should possess, the functionalities of the aforementioned materials as interfacial, charge transport, layers in OSCs and PVSCs are discussed in depth. It is concluded by providing guidelines for further developments that could significantly extend the implementation of these materials in solar cells.

In this study, ZnO-WO3 nanoparticles are prepared by sol-gel technique. Various characterization techniques have been utilized for studying morphological, optical, as well as structural properties of the synthesized nanostructures. Two sets of inverted organic solar cells have been constructed by the chemically synthesized ZnO-WO3 nanoparticles as electron transport layer (ETL) and as hole transport layer (HTL) and the solar cell characteristics were examined. The first solar cell (device A) employing ZnO-WO3 as ETL was fabricated with configuration ITO/ZnO/ZnO-WO3/PTB7-Th:PC71BM/MoO3/Ag, while the other solar cell (device B) employing ZnO-WO3 as HTL was fabricated with structure ITO/ZnO/PTB7-Th:PC71BM/ZnO-WO3/MoO3/Ag. In comparison to the device A with ZnO-WO3 as ETL, a remarkable improvement is seen in device B with ZnO-WO3 as HTL. An efficiency of 1.88% is observed in device B in comparison to the efficiency of 0.64% in device A. The results suggest that ZnO-WO3 nanoparticles have great potential in photovoltaics.

Global energy demand is increasing; thus, emerging renewable energy sources, such as organic solar cells (OSCs), are fundamental to mitigate the negative effects of fuel consumption. Within OSC’s advancements, the development of efficient and stable interface materials is essential to achieve high performance, long-term stability, low costs, and broader applicability. Inorganic and nanocarbon-based materials show a suitable work function, tunable optical/electronic properties, stability to the presence of moisture, and facile solution processing, while organic conducting polymers and small molecules have some advantages such as fast and low-cost production, solution process, low energy payback time, light weight, and less adverse environmental impact, making them attractive as hole transporting layers (HTLs) for OSCs. This review looked at the recent progress in metal oxides, metal sulfides, nanocarbon materials, conducting polymers, and small organic molecules as HTLs in OSCs over the past five years. The endeavors in research and technology have optimized the preparation and deposition methods of HTLs. Strategies of doping, composite/hybrid formation, and modifications have also tuned the optical/electrical properties of these materials as HTLs to obtain efficient and stable OSCs. We highlighted the impact of structure, composition, and processing conditions of inorganic and organic materials as HTLs in conventional and inverted OSCs.

In this work, we report copper bromide (CuBr) as an efficient, inexpensive, and solution-processable hole transport layer (HTL) for organic solar cells (OSCs) for the first time. To examine the effectiveness of the material in general, three different solvents such as acetonitrile (MeCN), dimethyl sulfoxide (DMSO), and dimethylformamide (DMF) are used for solution-processing thin-film deposition of CuBr. CuBr thin films deposited from different solvents show high transparency and no significant difference has been observed in absorption in the visible and near-IR range, whereas a slight difference has been found in the near-UV range by changing the solvents. Furthermore, two most studied combinations of the active layer such as PTB7/PC71BM and PCDTBT:/PC71BM are used for device fabrication with geometry of ITO/CuBr(HTL) active layer/Al. By using CuBr as a HTL in OSCs, the power conversion efficiencies (PCEs) have been achieved to up to 5.16 and 4.72% with PTB7/PC71BM and PCDTBT/PC71BM active layers, respectively. The CuBr film from DMF solvent shows highest PCE as compared to films deposited from DMSO and MeCN solvents. Different solvents used for HTL deposition have a major effect on the fill factor (FF), while very little difference on open circuit voltage (Voc) and short circuit current (Jsc) has been observed. It may be mentioned here that a small difference of device parameters (PCE, FF, Jsc, and Voc) has been observed in the devices using the HTL deposited from DMF and DMSO solvents, whereas a significant difference of the device parameters has been found in devices using the HTL from MeCN solvent.

The emergence of nonfullerene small-molecule acceptors (NFSMA) with the advantages of synthetic versatility, high absorption coefficient in wide wavelength range, and high thermal stability has attained the power conversion efficiency (PCE) exceeding 19% for resulted organic solar cells (OSCs) with the optimization of interface engineering and active layer morphology. Interfacial layers including both hole transporting layer (HTL) and electron transporting layer (ETL) are equally important in the OSCs for facilitating electron and hole extraction from the bulk heterojunction (BHJ) photoactive layer by the respective electrodes. In this Review, we summarize the recent progress in the materials used as HTL and ETL in conventional and inverted OSCs on the basis of their effect on the PCE. Finally, the prospects of HTL and ETL materials for NFSMA-OSCs will be provided.

The pertinence of different layers of organic solar cells (OSCs), namely the active or dynamic layer, the hole transport layer (HTL), and the electron transport layer (ETL), as well as the presentation of OSC boundaries, was examined using electrical modelling through the OghmaNano software, previously known as GPVDM (General Purpose Photovoltaic Device Model) software. This study is essentially revolved around PTB7: PC70BM as the active layer. The device structure-FTO/ PEDOT:PSS /PTB7: PC70BM/ZnO/Al was employed. Here, ZnO and PEDOT: PSS were taken as ETL and HTL, separately. The thicknesses of the HTL, ETL, as well as the active layer, were adjusted, and the corresponding changes in the OSC parameters were observed. The outcomes showed that the highest power conversion efficiency (PCE) acquired was 12.55%, coupled with short circuit current density (15.69 mAcm-2), open-circuit voltage (1.030 V), and fill factor (77.6%). Further enhancements in the PCE and different boundaries of OSC can be achieved by changing the engineering of the device (OSC) and the materials.

A low-cost and low-temperature processable zinc oxide-polyethylenimine (ZnO:PEI) nano-composite as cathode buffer layer for organic and perovskite solar cells

Thin films of tungstite (WO3·H2O) nanoparticles have been used as a hole transporting layer (HTL) in organic solar cells and demonstrated good performances.

Aqueous solution processed tetrasulphonated copper phthalocyanine (TS-CuPc):MoO3 as an efficient hole transporting layer in organic solar cells

Thanks to huge research efforts, organic solar cells have become serious candidates in the field of renewable energy sources, with reported power conversion efficiencies above 19% and operating lifetime surpassing decades. In the thin film stack composing the organic solar cell, the transport layers at interfaces play a key role, as important as the photoactive material itself. Both electron (ETL) and hole (HTL) transport layers are indeed directly involved in the efficiency and stability of the devices, due to the very specific properties required for these interfaces. Focusing on the HTL interface, a large number of materials has been used in organic solar cells, such as 2D materials, conductive polymers or transition metal oxides. In this review, we present the evolution and recent advances in HTL materials that have been employed in manufacturing organic solar cells, by describing their properties and deposition processes, and also relating their use with the fullerene or the new non-fullerene acceptors in the active layer.

Hole transporting layers (HTLs), strategically positioned between electrode and light absorber, play a pivotal role in shaping charge extraction and transport in organic solar cells (OSCs). However, the commonly used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL, with its hygroscopic and acidic nature, undermines the operational durability of OSC devices. Herein, an environmentally friendly approach is developed utilizing nickel acetate tetrahydrate (NiAc·4H2O) and [2-(9H-carbazol-9-yl)ethyl] phosphonic acid (2PACz) as the NiAc·4H2O/2PACz HTL, aiming at overcoming the limitations posed by the conventional PEDOT:PSS one. Encouragingly, a remarkable power conversion efficiency (PCE) of 19.12% is obtained for the OSCs employing NiAc·4H2O/2PACz as the HTL, surpassing that of devices with the PEDOT:PSS HTL (17.59%), which is ranked among the highest ones of OSCs. This improvement is attributed to the appropriate work function, enhanced hole mobility, facilitated exciton dissociation efficiency, and lower recombination loss of NiAc·4H2O/2PACz-based devices. Furthermore, the NiAc·4H2O/2PACz-based OSCs exhibit superior operational stability compared to their PEDOT:PSS-based counterparts. Of significant note, the NiAc·4H2O/2PACz HTL demonstrates a broad generality, boosting the PCE of the PM6:PY-IT and PM6:Y6-based OSCs from 16.47% and 16.79% (with PEDOT:PSS-based analogs as HTLs) to 17.36% and 17.57%, respectively. These findings underscore the substantial potential of the NiAc·4H2O/2PACz HTL in advancing OSCs, offering improved performance and stability, thereby opening avenue for highly efficient and reliable solar energy harvesting technologies.

Solvents effects on the hole transport layer in organic solar cells performance

Influence of the modification of annealing parameters on solution-processed metal oxide ETL buffer layers, and a comparative study of spin-coated and thermally evaporated MoOx HTL for use in an inverted polymer solar cell

A new series of Fischer carbenes have been synthetized and examined as hole-transporting or electron-transporting layers (HTLs or ETLs) in the fabrication of organic solar cells (OSCs). The synthesis of three Fischer aminocarbene complexes with the general formula [Cr(CO)5{C(NHCH2)Ar}] (Ar = 2-pyridyl (3a), 3-pyridyl (3b) and 4-pyridyl (3c)) is reported. The molecular structure of complex 3b has been confirmed by X-ray analysis. In order to study the possible applications of the three Fischer aminocarbenes in OSCs, thin films of these complexes were prepared using a vacuum deposition process. These organometallic films were chemically and morphologically characterized by IR spectroscopy, SEM, AFM and XRD. According to the IR and Tauc analysis, the vacuum deposition process generates thin films free of impurities with an activation energy of 4.0, 2.7 and 2.1 eV for 3a, 3b y 3c, respectively. The UV-vis spectra of the amorphous aminocarbene films show that they are practically transparent to the visible radiation of the electromagnetic spectrum. This is due to the fact that their absorption is located mainly in the ultraviolet range. Two OSCs with bulk-heterojunction configuration were manufactured in order to prove the use of the aminocarbenes as ETL o HTL. The aminocarbene [Cr(CO)5{C(NHCH2) 4-pyridyl}] (3c) proved to be suitable as ETL with a fill factor (FF) of 0.23 and a short circuit current density (JSC) of 1.037 mA/cm2.