Hole Selective Layer Research Articles

Halogenated Polycyclic Aromatic Hydrocarbon for Hole Selective Layer/Perovskite Interface Modification and Passivation for Efficient Perovskite‐Organic Tandem Solar Cells with Record Fill Factor

AbstractPerovskite whentandemed with organic photovoltaics (OPV) for double‐junctions have efficiencypotentials over 40%. However, there is still room for improvement suchas better current matching, higher fill factor, as well as lower voltage and fill factor losses in the top perovskite cell. Here weaddress the issue associated with the top perovskite cell by utilising anovel halogenated polycyclic aromatic hydrocarbon compound, 1‐naphthylammoniumchloride (NA─Cl) playing dual roles of surface modification for the hole selectivelayer (HSL) and passivation of HSL/perovskiteinterface. Results of X‐ray photoelectron spectroscopy and density functionaltheory calculations reveal that NA─Cl retains self‐assembly property for the HSLwhile demonstrating high dipole moment and polarizability. This induces asurface dipole at the HSL/perovskite interface reducing the energetic barrierfor hole extraction by 210 meV thereby enhancing voltage output and fill factorof the device. Such scheme when implemented in a high bandgap (1.78 eV)perovskite solar cell, results in a respectable efficiency of 19.7% and thehighest fill factor of 85.4% amongst those of 1.78 eV perovskite cells reported.We have also achieved 23% cell efficient monolithic perovskite‐OPV tandem withan impressive fill factor of 84%, which is the highest for perovskite‐OPVtandem cells reported to‐date.

Co-optimization of CuBi2O4 photocathode by heterojunction and hole-selective layer for efficient photoelectrochemical water splitting

Co-optimization of CuBi2O4 photocathode by heterojunction and hole-selective layer for efficient photoelectrochemical water splitting

Synergistic Buried Interface Regulation of Tin-Lead Perovskite Solar Cells via Co-Self-Assembled Monolayers.

Tin-lead (Sn-Pb) perovskite solar cells (PSCs) hold considerable potential for achieving efficiencies near the Shockley-Queisser (S-Q) limit. Notably, the inverted structure stands as the preferred fabrication method for the most efficient Sn-Pb PSCs. In this regard, it is imperative to implement a strategic customization of the hole selective layer to facilitate carrier extraction and refine the quality of perovskite films, which requires effective hole selectivity and favorable interactions with Sn-Pb perovskites. Herein, we propose the development of Co-Self-Assembled Monolayers (Co-SAM) by integrating both [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) and glycine at the buried contacts. The one-step deposition process employed in the fabrication of the Co-SAM ensures uniform coverage, resulting in a homogeneous surface potential. This is attributed to the molecular interactions occurring between 2PACz and glycine in the processing solution. Furthermore, the amine (-NH2) and ammonium (-NH3+) groups in glycine effectively passivate Sn4+ defects at the buried interface of Sn-Pb perovskite films, even under thermal stress. Consequently, the synergistic buried interface regulation of Co-SAM leads to a power conversion efficiency (PCE) of 23.46%, which outperforms devices modified with 2PACz or glycine alone. The Co-SAM-modified Sn-Pb PSC demonstrates enhanced thermal stability, maintaining 88% of its initial PCE under 65 °C thermal stress for 590 h.

Heavy Boron-Doped Silicon Tunneling Inter-layer Enables Efficient Silicon Heterojunction Solar Cells.

P-type hydrogenated nanocrystalline silicon (nc-Si:H) has been used as a hole-selective layer for efficient n-type crystalline silicon heterojunction (SHJ) solar cells. However, the presence of an additional valence band offset at the interface between intrinsic amorphous hydrogenated silicon and p-type nc-Si:H films will limit the hole carrier transportation. In this work, it has been found that when a heavily boron-doped silicon oxide layer deposited with high hydrogen dilution to silane (pB) was inserted into their interface, the fill factor of SHJ solar cells increases 3% absolutely because of the reduced valence band offset and the increased opportunity to provide a hopping tunnel assisted by the doping energy level and valence band tail states. Furthermore, the additional boron incorporation in intrinsic amorphous silicon adjacent to pB helps to enhance the built-in electric field, thus increasing the hole selectivity. By these means, the power conversion efficiency was improved from 23.9% to approximately 25%.

Repairing Interfacial Defects in Self-Assembled Monolayers for High-Efficiency Perovskite Solar Cells and Organic Photovoltaics through the SAM@Pseudo-Planar Monolayer Strategy.

Lately, carbazole-based self-assembled monolayers (SAMs) are widely employed as effective hole-selective layers (HSLs) in inverted perovskite solar cells (PSCs). Nevertheless, these SAMs tend to aggregate in solvents due to their amphiphilic nature, hindering the formation of a monolayer on the ITO substrate and impeding effective passivation of deep defects in the perovskites. In this study, a series of new SAMs including DPA-B-PY, CBZ-B-PY, POZ-B-PY, POZ-PY, POZ-T-PY, and POZ-BT-PY are synthesized, which are employed as interfacial repairers and coated atop CNph SAM to form a robust CNph SAM@pseudo-planar monolayer as HSL in efficient inverted PSCs. The CNph SAM@pseudo-planar monolayer strategy enables a well-aligned interface with perovskites, synergistically promoting perovskite crystal growth, improving charge extraction/transport, and minimizing nonradiative interfacial recombination loss. As a result, the POZ-BT-PY-modified PSC realizes an impressively enhanced solar efficiency of up to 24.45% together with a fill factor of 82.63%. Furthermore, a wide bandgap PSC achieving over 19% efficiency. Upon treatment with the CNph SAM@pseudo-planar monolayer, also demonstrates a non-fullerene organic photovoltaics (OPVs) based on the PM6:BTP-eC9 blend, which achieves an efficiency of 17.07%. Importantly, these modified PSCs and OPVs all show remarkably improved stability under various testing conditions compared to their control counterparts.

TCAD simulation of germanium-based heterostructure solar cell employing molybdenum oxide as a hole-selective layer

Molybdenum Oxide (MoO x ) has been used as a hole-extraction film for photovoltaic (PV) applications; however, its interaction with Germanium (Ge)-based solar cells is less understood. For the first time, this paper aims to physically model the Ge solar cell that incorporates MoO x for hole transportation at the front side of the PV device facing the sunlight. However, the charge transportation process within the PV device is influenced by several design parameters that need optimization. A higher work function of MoO x increases the barrier height against minority carriers of electrons which is beneficial for extricating holes at the front interface of MoO x /Ge. A progressive reduction in the recombination of charge carriers has been observed by including a passivation layer of amorphous silicon (i-a-Si:H). Similarly, inserting a passivation and back surface field (BSF) stack of i-a-Si:H strengthens the electric field and likewise reduces the recombination at the rear side of the device. An enhanced doping concentration of BSF assists in the favorable alignment of energy bands for improved charge transportation within the solar cell as the rear passivation maintains the field strength for accelerated movement of charge carriers. However, optimizing the thickness of the front-passivation film is challenging due to the parasitic absorption of light at larger thicknesses. A comparative study with the reference device revealed that the proposed device exhibited a step-increase in the conversion efficiency (η) from 4.23% to 13.10%, with a higher J sc of 46.4 mA cm−2, V oc of 383 mV, and FF of 74%. The proposed study is anticipated to meet the research gap in the physical device modelling of Ge-based solar cells employing high work function MoO x as a carrier-selective layer that could be conducive to the development of highly efficient multijunction solar cells.

Enhancement of Efficiency of Perovskite Solar Cells with Hole-Selective Layers of Rationally Designed Thiazolo[5,4-d]thiazole Derivatives.

We introduce thiazolo[5,4-d]thiazole (TT)-based derivatives featuring carbazole, phenothiazine, or triphenylamine donor units as hole-selective materials to enhance the performance of wide-bandgap perovskite solar cells (PSCs). The optoelectronic properties of the materials underwent thorough evaluation and were substantially fine-tuned through deliberate molecular design. Time-of-flight hole mobility TTs ranged from 4.33 × 10-5 to 1.63 × 10-3 cm2 V-1 s-1 (at an electric field of 1.6 × 105 V cm-1). Their ionization potentials ranged from -4.93 to -5.59 eV. Using density functional theory (DFT) calculations, it has been demonstrated that S0 → S1 transitions in TTs with carbazolyl or ditert-butyl-phenothiazinyl substituents are characterized by local excitation (LE). Mixed intramolecular charge transfer (ICT) and LE occurred for compounds containing ditert-butyl carbazolyl-, dimethoxy carbazolyl-, or alkoxy-substituted triphenylamino donor moieties. The selected derivatives of TT were used for the preparation of hole-selective layers (HSL) in PSC with the structure of glass/ITO/HSLs/Cs0.18FA0.82Pb(I0.8Br0.2)3/PEAI/PC61BM/BCP/Ag. The alkoxy-substituted triphenylamino containing TT (TTP-DPA) has been demonstrated to be an effective material for HSL. Its layer also functioned well as an interlayer, improving the surface of control HSL_2PACz (i.e., reducing the surface energy of 2PACz from 66.9 to 52.4 mN m-1), thus enabling precise control over perovskite growth energy level alignment and carrier extraction/transportation at the hole-selecting contact of PSCs. 2PACz/TTP-DPA-based devices showed an optimized performance of 19.1 and 37.0% under 1-sun and 3000 K LED (1000 lx) illuminations, respectively. These values represent improvements over those achieved by bare 2PACz-based devices, which attained efficiencies of 17.4 and 32.2%, respectively. These findings highlight the promising potential of TTs for the enhancement of the efficiencies of PSCs.

Interfacial Band Engineering of Highly Efficient PEDOT:PSS/p‐Si/ZnO Heterojunction Solar Cells

Hybrid heterojunction solar cells (HHSCs) using different active materials as hole‐selective transport layers and electron‐selective transport layers show great potential in both low cost and high power conversion efficiency (PCE). Herein, PEDOT:PSS/p‐Si/ZnO backcontact heterojunction solar cells are prepared using the simple low‐temperature solution method. PEDOT:PSS is introduced into p‐Si‐based solar cells as an antireflective and passivation layer to optimize device performance. The effect of the work function (WF) of ZnO on device performance is investigated, and a PCE of 10.74% is achieved using low‐WF ZnO. In addition, the PEDOT:PSS layer is doped with Nafion, and the surface passivation quality of the p‐Si is dramatically enhanced. By optimizing the doping concentration of Nafion, the PCE of the optimized device reaches 11.43%, which is currently the highest PCE for p‐Si‐based solar cells using solution method. The findings provide a simple and promising method to achieve high‐performance PEDOT:PSS/p‐Si/ZnO HHSCs.

A Hole-Selective Self-Assembled Monolayer for Both Efficient Perovskite and Organic Solar Cells.

Self-assembled monolayers (SAMs) emerging as promising hole-selective layers (HSLs) are advantageous for facile processability, low cost, and minimal material consumption in the fabrication of both perovskite solar cells (PSCs) and organic solar cells (OSCs). However, owing to the different nature between perovskites and organic semiconductors, few SAMs were reported to effectively accommodate both PSCs and OSCs at the same time. In this regard, a universally applicable SAM that can accommodate both perovskites and organic semiconductors could be desirable for simplifying cell manufacturing, especially from an industrial perspective. In this work, we designed a SAM, TDPA-Cl by introducing chlorinated phenothiazine as the headgroup and linking with anchor phosphonic acid through a butyl chain. The resulting dense SAM was carefully characterized in terms of molecular bonding, surface morphology, and packing density, and its functions in OSCs and PSCs were discussed from the aspects of interactions with the absorber layer, energy level alignment, and charge-selective dipoles. The PM6:Y6-based OSCs with TDPA-Cl SAM as the HSL showed a superior performance to those with PEDOT:PSS. Furthermore, the universality was proved with an efficiency of 17.4% in the D18:Y6 system. In PSCs, the TDPA-Cl-based devices delivered a better performance of 22.4% than the PTAA-based devices (20.8%) with improved processability and reproducibility. This work represents a SAM with reasonably good compromise between the differing requirements of OSCs and PSCs.

Carbon Electrodes for Perovskite Photovoltaics: Interfacial Properties, Meta‐analysis, and Prospects

Carbon electrodes have gained significant attention as a cost‐effective, sustainable, stable, and scalable replacement for metal electrodes in perovskite solar cells (PSCs). However, traditional carbon‐electrode‐based PSCs (C‐PSCs) lack a hole‐selective layer (HSL) due to their incompatibility with the most effective organic HSLs employed in the PSC literature. In turn, the absence of an HSL has been identified as one of the main factors hindering the performance of C‐PSCs. Consequently, numerous studies have recognized the pivotal significance of the region between the perovskite absorber and the carbon electrode in C‐PSCs, proposing various interfacial engineering strategies to improve the performance of these solar cells. Given the rapid evolution of this field, an up‐to‐date and comprehensive review of C‐PSCs is in order. Key areas of focus of this review include the shift from high‐temperature to low‐temperature carbon electrodes, strategies to improve energetic alignment at the interface, novel approaches such as hole‐selective bilayers, and alternative carbon deposition methods to reduce solvent damage. Additionally, this review presents a comprehensive meta‐analysis—the first of its kind in the C‐PSC literature—to assess how various interfacial modifications impact critical C‐PSC performance metrics, offering valuable insights for future advancements in the field.

Defect‐Passivating and Stable Benzothiophene‐Based Self‐Assembled Monolayer for High‐Performance Inverted Perovskite Solar Cells

AbstractEffective passivation of defects at the buried interface between the perovskite absorber and hole‐selective layer (HSL) is crucial for achieving high performance in inverted perovskite solar cells (PSCs). Additionally, the HSL needs to possess compact molecular packing and intrinsic photo‐ and thermo‐stability to ensure long‐term operation of the devices. In this study, a novel MeO‐BTBT‐based self‐assembled monolayer (SAM) is reported to serve as an efficient HSL in inverted PSCs. Compared to the well‐established carbazole‐containing SAM MeO‐2PACz, MeO‐BTBT has flat and more extended conjugation with large atomic radius of the sulfur atom. These induce stronger intermolecular interactions to enable more ordered and compact SAM to be formed on indium–tin oxide (ITO) substrates. Meanwhile, the sulfur atoms in MeO‐BTBT can coordinate with Pb2+ ions to passivate the defects at the buried interface of perovskite absorber. The derived perovskite films show both high photoluminescence (PL) quantum yield (13.2%) and a long lifetime (7.2 µs). The PSCs based on MeO‐BTBT show a PCE of 24.53% with an impressive fill factor of 85.3%. The PCEs of MeO‐BTBT‐based devices can maintain ≈95% of their initial values after being aged at 65 °C for more than 1000 h or continuous operation under 1‐sun illumination.

Molecularly Engineered Self-Assembled Monolayers as Effective Hole-Selective Layers for Organic Solar Cells

Molecularly Engineered Self-Assembled Monolayers as Effective Hole-Selective Layers for Organic Solar Cells

Perovskite Solar Cells With Modified Carbon Electrode and CuSCN Interlayer Processed Under Ambient Conditions

Carbon‐based perovskite solar cells (PSCs) have the advantages of a long lifetime and are compatible with highly scalable manufacturing processes. The use of carbon electrodes and the absence of a hole selective layer (HSL) promote a simplified fabrication process. However, the efficiency of HSL‐free carbon‐based PSCs is inferior to PSCs that utilize metal electrodes and HSL due to poor hole extraction at the perovskite/carbon interface. To overcome those issues, researchers added an interlayer on the perovskite/carbon interface or incorporated additive material into the carbon layer. However, there is limited research on utilizing both strategies to improve carbon‐based PSC performance. Here, we use CuSCN as an interlayer between the perovskite/carbon interface and a carbon additive in carbon‐based PSCs. By utilizing both strategies, the charge transfer of carbon‐based PSC was significantly improved compared to carbon‐based PSC utilizing only one improvement strategy. Confirmed by photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) characterizations, the CuSCN interlayer and CuSCN‐incorporated carbon electrode enable more efficient hole transfer, resulting in an increased power conversion efficiency from 0.58% to 5.06%. The proposed PSC structure shows promising results for further improving carbon‐based PSC performance.

Simultaneously enhancing hole extraction and defect passivation with more conductive hole-selective self-assembled molecules for efficient inverted perovskite solar cells

Suppressing the interfacial energy losses of the buried hole-selective layer (HSL) is essential to upgrade the power conversion efficiencies (PCEs) of inverted perovskite solar cells (PSCs). In this regard, the...

Rational molecular design of multifunctional self-assembled monolayers for efficient hole selection and buried interface passivation in inverted perovskite solar cells.

Self-assembled monolayers (SAMs) have been widely employed as the bottom-contact hole-selective layer (HSL) in inverted perovskite solar cells (PSCs). Besides manipulating the electrical properties, molecularly engineering the SAM provides an opportunity to modulate the perovskite buried interface. Here, we successfully introduced Lewis-basic oxygen and sulfur heteroatoms through rational molecular design of asymmetric SAMs to obtain two novel multifunctional SAMs, CbzBF and CbzBT. Detailed characterization of single-crystal structures and device interfaces shows that enhanced packing, more effective ITO work function adjustment, and buried interface passivation were successfully achieved. Consequently, the champion PSC employing CbzBT showed an excellent power conversion efficiency (PCE) of 24.0% with a high fill factor of 84.41% and improved stability. This work demonstrates the feasibility of introducing defect-passivating heterocyclic groups into SAM molecules to help passivate the interfacial defects in PSCs. The insights gained from this molecular design strategy will accelerate the development of new multifunctional SAM HSLs for efficient PSCs.

Achieving a high open-circuit voltage of 1.339 V in 1.77 eV wide-bandgap perovskite solar cells via self-assembled monolayers

A self-assembled monolayer of DCB-BPA hole-selective layer facilitates the improved buried-interface quality, leading to a certified VOC of 1.339 V of 1.77 eV wide-bandgap perovskite solar cells.

Toward Efficient and Fully Scalable Sputtered NiOx‐Based Inverted Perovskite Solar Modules via Co‐Ordinated Modification Strategies

Sputtered nickel oxide (NiOx) has become one of the most promising inorganic hole transport layers for p–i–n perovskite solar cells (PSCs) due to its appealing features such as its robust nature, low material cost, and easy integration to tandem structures and large‐area applications. However, the main drawback with NiOx‐based PSCs is typically low open‐circuit voltage (VOC) due to the inferior energy‐level alignment, low charge mobility, and high recombination at the interface. Herein, two types of phosphonic acid self‐assembled monolayers (SAMs) deposited by blade coating as an interfacial layer to modulate the sputtered NiOx/perovskite interface properties are used. While sputtered NiOx serves as a conformally coated hole selective layer, the ultrathin SAM interlayer facilitates the hole extraction and minimizes the energy loss at the interface. Co‐ordinately introduced stabilizing additive, namely octadecyl 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propionate (I‐76), further improves the device performance of NiOx/SAM‐based PSCs, resulting in VOC of 1.14 V and a power conversion efficiency of 21.8%. By applying these strategies for perovskite module upscaling, aperture area module efficiencies of 19.7%, 17.5%, and 15.5% for perovskite minimodules of 4, 16, and 100 cm2 are demonstrated, corresponding to active area module efficiencies of 20.4%, 18.0%, and 16.4%, respectively.

Growth of Cr2O3 on n-Silicon Substrate using AACVD and its Application as a Hole Selective Layer

Growth of Cr2O3 on n-Silicon Substrate using AACVD and its Application as a Hole Selective Layer

Fully Aromatic Self-Assembled Hole-Selective Layer toward Efficient Inverted Wide-Bandgap Perovskite Solar Cells with Ultraviolet Resistance.

Ultraviolet-induced degradation has emerged as a critical stability concern impeding the widespread adoption of perovskite solar cells (PSCs), particularly in the context of phase-unstable wide-band gap perovskite films. This study introduces a novel approach by employing a fully aromatic carbazole-based self-assembled monolayer, denoted as (4-(3,6-dimethoxy-9H-carbazol-9-yl)phenyl)phosphonic acid (MeO-PhPACz), as a hole-selective layer (HSL) in inverted wide-band gap PSCs. Incorporating a conjugated linker plays a pivotal role in promoting the formation of a dense and highly ordered HSL on substrates, facilitating subsequent perovskite interfacial interactions, and fostering the growth of uniform perovskite films. The high-quality film could effectively suppress interfacial non-radiative recombination, improving hole extraction/transport efficiency. Through these advancements, the optimized wide-band gap PSCs, featuring a band gap of 1.68 eV, attain an impressive power conversion efficiency (PCE) of 21.10 %. Remarkably, MeO-PhPACz demonstrates inherent UV resistance and heightened UV absorption capabilities, substantially improving UV resistance for the targeted PSCs. This characteristic holds significance for the feasibility of large-scale outdoor applications.

Fully Aromatic Self‐Assembled Hole‐Selective Layer toward Efficient Inverted Wide‐Bandgap Perovskite Solar Cells with Ultraviolet Resistance

AbstractUltraviolet‐induced degradation has emerged as a critical stability concern impeding the widespread adoption of perovskite solar cells (PSCs), particularly in the context of phase‐unstable wide‐band gap perovskite films. This study introduces a novel approach by employing a fully aromatic carbazole‐based self‐assembled monolayer, denoted as (4‐(3,6‐dimethoxy‐9H‐carbazol‐9‐yl)phenyl)phosphonic acid (MeO‐PhPACz), as a hole‐selective layer (HSL) in inverted wide‐band gap PSCs. Incorporating a conjugated linker plays a pivotal role in promoting the formation of a dense and highly ordered HSL on substrates, facilitating subsequent perovskite interfacial interactions, and fostering the growth of uniform perovskite films. The high‐quality film could effectively suppress interfacial non‐radiative recombination, improving hole extraction/transport efficiency. Through these advancements, the optimized wide‐band gap PSCs, featuring a band gap of 1.68 eV, attain an impressive power conversion efficiency (PCE) of 21.10 %. Remarkably, MeO‐PhPACz demonstrates inherent UV resistance and heightened UV absorption capabilities, substantially improving UV resistance for the targeted PSCs. This characteristic holds significance for the feasibility of large‐scale outdoor applications.