Chen Weijie

An internal encapsulation strategy with polymer PVB modified at the perovskite/electron transport layer interface for inverted perovskite solar cells (PSCs) is designed. In this way, a better energy-level alignment, reduced non-radiative recombination, and mitigated ion migration is obtained. As a result, PSCs with champion power conversion efficiency of 22.47% are achieved with improved stability and suppressed lead leakage.

Abstract

Significant progress is made in perovskite solar cells (PSCs) with high power conversion efficiency (PCE). However, the potential issue of lead leakage creates a critical challenge to its commercialization. Therefore, a convenient internal encapsulation strategy is proposed by introducing a polyvinyl butyral (PVB) polymer at the perovskite/electron transport layer interface. This strategy enhances the performance of PSCs and effectively suppresses lead leakage. The introduced PVB layer plays a crucial role in mitigating ion migration, optimizing energy levels, and preventing moisture penetration. Thus, PSCs with PVB modifications generally perform better, with an improved PCE of 22.47% and reduced hysteresis. Furthermore, these modified devices exhibit enhanced stability under light soaking and thermal stress, effectively mitigating lead leakage. This innovative approach not only enhances the efficiency of PSCs but also addresses the challenges associated with lead leakage, paving the way for more sustainable and commercially viable solar cell technologies.

Publication date: July 2024

Source: Nano Energy, Volume 126

Author(s): Nitin Mallik, Javid Hajhemati, Mathieu Frégnaux, Damien Coutancier, Ashish Toby, Shan-Ting Zhang, Claudia Hartmann, Elif Hüsam, Ahmed Saleh, Thomas Vincent, Olivier Fournier, Regan G. Wilks, Damien Aureau, Roberto Félix, Nathanaelle Schneider, Marcus Bär, Philip Schulz

Publication date: 19 June 2024

Source: Joule, Volume 8, Issue 6

Author(s): Seul-Gi Kim, George C. Fish, Etienne Socie, Aaron T. Terpstra, Dong-Am Park, Kai Zhu, Michael Grätzel, Jacques-E. Moser, Nam-Gyu Park

Ethylenedioxythiophene was adopted to construct small molecular donor with multiple conformation locks, which can serve as efficient guest donor in ternary organic solar cells to provide cascade energy levels and two-dimensional charge transport channels, thus enabling high efficiency of 19.3 % compared to 18.2 % of the binary device.

Abstract

Ternary organic solar cells (T-OSCs) represent an efficient strategy for enhancing the performance of OSCs. Presently, the majority of high-performance T-OSCs incorporates well-established Y-acceptors or donor polymers as the third component. In this study, a novel class of conjugated small molecules has been introduced as the third component, demonstrating exceptional photovoltaic performance in T-OSCs. This innovative molecule comprises ethylenedioxythiophene (EDOT) bridge and 3-ethylrhodanine as the end group, with the EDOT unit facilitating the creation of multiple conformation locks. Consequently, the EDOT-based molecule exhibits two-dimensional charge transport, distinguishing it from the thiophene-bridged small molecule, which displays fewer conformation locks and provides one-dimensional charge transport. Furthermore, the robust electron-donating nature of EDOT imparts the small molecule with cascade energy levels relative to the electron donor and acceptor. As a result, OSCs incorporating the EDOT-based small molecule as the third component demonstrate enhanced mobilities, yielding a remarkable efficiency of 19.3 %, surpassing the efficiency of 18.7 % observed for OSCs incorporating thiophene-based small molecule as the third component. The investigations in this study underscore the excellence of EDOT as a building block for constructing conjugated materials with multiple conformation locks and high charge carrier mobilities, thereby contributing to elevated photovoltaic performance in OSCs.

A flexible transparent electrode has been developed utilizing an eco-friendly ethyl cellulose substrate and silver nanowires. Based on this electrode, a flexible organic solar cell is successfully fabricated, achieving an impressive efficiency exceeding 18%.

Flexibility is a key advantage of organic solar cells (OSCs), and the power conversion efficiencies (PCEs) of flexible OSCs (FOSCs) are primarily constrained by flexible transparent electrodes (FTEs). While much attention has been devoted to the study of conductive layers on FTEs, the importance of flexible substrates in influencing the properties of FTEs and the performance of FOSCs is often overlooked. In this study, an FTE is developed using an eco-friendly ethyl cellulose (EC) substrate and silver nanowires (AgNWs) as the conductive electrode. The FTE exhibits a high transmittance of up to 88% at 550 nm and a low sheet resistance of 17.65 Ω/□. Consequently, FOSCs based on the EC/PI FTEs achieve a remarkable PCE of 18.05%, comparable to that on the rigid ITO substrate. The flexible devices also demonstrate excellent bending and peeling durability even under extreme bending conditions.

Crucial advancements are still required to realize scalable and reliable fabrication processes for perovskite photovoltaics. The hybrid two-step process combines evaporated PbI₂ with inkjet-printed organic precursor materials, to ensure thin-film control and high power conversion efficiencies. Introducing a dimethyl-sulfoxide-vapor-treatment facilitates stoichiometry by enhancing PbI₂ porosity for optimal conversion. In the results, a promising, scalable process is demonstrated for reliable perovskite deposition, paving the path toward industrialization.

Perovskite photovoltaics are on their way to commercialization, but crucial advancements are still required to realize scalable and reliable fabrication processes Concerning solution processing of perovskite top solar cells, the hybrid two-step process offers an auspicious combination of good thin-film formation control, even on textures, and high power conversion efficiencies (PCEs). Herein, a scalable fabrication process that consists of a hybrid two-step process and combines evaporated PbI₂ with inkjet-printed organic precursor materials is addressed. It is shown that optimizing the printing parameters enables high PCEs, high reproducibility, and the potential for conformal growth on textured silicon. The perovskite films are free of macroscopic drying effects and omit the use of toxic solvents. To achieve optimal conversion, the morphology of the PbI₂ thin film and the selected resolution in the printing process are decisive. To facilitate intermixing and enable stoichiometry, a dimethyl sulfoxide vapor treatment is introduced to increase the PbI₂ porosity. Reproducible PCEs are demonstrated with champion devices showing 18.2% which are on par with spin-coated counterparts. In the results, it is demonstrated that the hybrid two-step process with an inkjet-printed second step is a promising scalable process for reliable and high-quality perovskite deposition even on texture, thereby paving the path toward industrialization.

Publication date: 15 June 2024

Source: Nano Energy, Volume 125

Author(s): Tianqi Chen, Yuyang Bai, Xinyi Ji, Wanying Feng, Tainan Duan, Xue Jiang, Yuan-qiu-qiang Yi, Jifa Yu, Guanghao Lu, Xiangjian Wan, Bin Kan, Yongsheng Chen

This study discusses the sheet resistance optimization in the aluminum gallium indium phosphide (AlGaInP) subcell of multi-junction solar cells. It examines the electron mobility in lattice-matched (to gallium arsenide) AlGaInP and computes sheet resistances for rear–heterojunction cells with varying bandgap energy and absorber thickness. An optimized cell design is proposed, which reduces the series resistance by 5 mΩ cm².

The reduction of the series resistance in multi-junction solar cells is of high importance for attaining peak efficiencies in concentrator photovoltaics. This study showcases strategies to reduce the sheet resistance of the uppermost subcell of a direct wafer bonded four–junction devices, since it contributes significantly to the series resistance. Therefore, electron mobilities in n–type AlGaInP, lattice matched to GaAs, are investigated across bandgap energies between 1.9 and 2.1 eV and various doping concentrations. The sheet resistances for AlGaInP rear heterojunction cells are determined for the integration in a two terminal four-junction solar cell. The rear heterojunction cell architecture effectively addresses the sheet resistance optimization because it features a thick n-type doped absorption layer. The sheet resistance of our current world record quadruple-junction solar cell with 47.6% efficiency under the 665-fold concentrated AM1.5d spectrum is 550 Ω sq⁻¹. Herein, it is shown that optimizing the n-absorption layer in the 1.90 eV GaInP top cell can reduce the sheet resistance to 250 Ω sq⁻¹ without deteriorating the short–circuit current density and current matching. This reduction corresponds to a 5 mΩ cm² improvement in specific series resistance, which would elevate the efficiency of this device to 48.2%.

A SnO_x interfacial layer with gradient compositions has been designed to overcome the dilemma between interface defects and electrical properties. Owing to the formation of homojunction, the gradient SnO_x structure facilitates the charge extraction, enabling the perovskite–silicon tandem solar cells based on industrially fully-textured silicon to achieve a certified efficiency of over 28%.

Abstract

Atomic layer deposition (ALD) growth of conformal thin SnO _x films on perovskite absorbers offers a promising method to improve carrier-selective contacts, enable sputter processing, and prevent humidity ingress toward high-performance tandem perovskite solar cells. However, the interaction between perovskite materials and reactive ALD precursor limits the process parameters of ALD-SnO _x film and requires an additional fullerene layer. Here, it demonstrates that reducing the water dose to deposit SnO _x can reduce the degradation effect upon the perovskite underlayer while increasing the water dose to promote the oxidization can improve the electrical properties. Accordingly, a SnO _x buffer layer with a gradient composition structure is designed, in which the compositionally varying are achieved by gradually increasing the oxygen source during the vapor deposition from the bottom to the top layer. In addition, the gradient SnO _x structure with favorable energy funnels significantly enhances carrier extraction, further minimizing its dependence on the fullerene layer. Its broad applicability for different perovskite compositions and various textured morphology is demonstrated. Notably, the design boosts the efficiencies of perovskite/silicon tandem cells (1.0 cm²) on industrially textured Czochralski (CZ) silicon to a certified efficiency of 28.0%.

Self-assembled monolayers (SAM) modified nickel oxide (NiO_x) is used as a hole-selective layer in inverted perovskite solar cells and finally, the highest power conversion efficiency of 24.8% is achieved with excellent thermal stability by the highest coverage of SAM on NiO_x.

Abstract

Nickel oxide is one of the most promising hole-transporting materials in inverted perovskite solar cells (PSCs) but suffers from undesired reactions with perovskite which leads to limited device performance and stability. Self-assembled monolayers (SAMs) are demonstrated to effectively optimize the NiO_x/perovskite interface, but the significance of the compactness of the SAM at the interface is less investigated. Here, a series of methoxy-substituted triphenylamine functionalized benzothiadiazole (TBT) based SAM molecules, TBT-BA, TBT-FBA, and TBT-DBA, with benzoic acid, 2-fluorobenzoic acid and isophthalic acids as anchoring groups are used to modify NiO_x. TBT-BA with the simplest structure is demonstrated to form the densest SAM on NiO_x, thus optimized NiO_x/SAM/perovskite interface is achieved with enhanced charge collection and suppressed interfacial reaction and recombination. TBT-BA can also passivate the perovskite most effectively due to the highest binding energy toward perovskite, thus the corresponding inverted PSCs show the highest PCE of 24.8% and maintain 88.7% of the initial PCE after storage at 60 °C for 2635 h in the glovebox. The work provides important insights into designing SAM molecules for modification transporting layers for efficient and stable PSCs.

The incorporation of iodine (I₂) is shown to modulate the methylammonium chloride (MACl)-assisted growth of α-phase formamidinium perovskite (α-FAPbI₃), with a delayed release of volatile MACl and suppressed cation side reaction. The optimized device delivers an efficiency of 25.2% with an impressive fill factor (FF) of 84.2%, which is attributed to suppressed non-radiative recombination.

Abstract

The preferential growth of α-phase formamidinium perovskite (α-FAPbI₃) at low temperatures can be achieved with the incorporation of chloride-based additives, with methylammonium chloride (MACl) being the most common example. However, compared to other less-volatile chloride additives, MACl only remains in the growing perovskite film for a short time before evaporating during annealing, primarily influencing the early stages of film formation. In addition, evaporation of MACl as methylamine (MA⁰) and HCl can introduce a side reaction between MA⁰ and formamidinium (FA), undermining the compositional purity and phase stability of α-FAPbI₃. In this study, it is demonstrated that addition of iodine (I₂) into the FAPbI₃ precursor solution containing MACl suppresses the MA-FA side reaction during annealing. Additionally, MACl evaporation is delayed owing to strong interaction with triiodide. The added I₂ facilitates spontaneous growth of α-FAPbI₃ prior to annealing, with an improved bottom morphology due to the formation of fewer byproducts. Perovskite solar cells derived from an I₂-incorporated solution deliver a champion power conversion efficiency of 25.2% that is attributed to suppressed non-radiative recombination.

Herein, the often-overlooked PbI₂ residual and its detailed impact on device performance are thoroughly investigated. Leveraging effective PbI₂ management and precise regulation of the perovskite crystallization process, the champion devices achieve a PCE of 25.06% with long-term stability.

Abstract

While significant efforts in surface engineering have been devoted to the conversion process of lead iodide (PbI₂) into perovskite and top surface engineering of perovskite layer with remarkable progress, the exploration of residual PbI₂ clusters and the hidden bottom surface on perovskite layer have been limited. In this work, a new strategy involving 1-butyl-3-methylimidazolium acetate (BMIMAc) ionic liquid (IL) additives is developed and it is found that both the cations and the anions in ILs can interact with the perovskite components, thereby regulating the crystallization process and diminishing the residue PbI₂ clusters as well as filling vacancies. The introduction of BMIMAc ILs induces the formation of a uniform porous PbI₂ film, facilitating better penetration of the second-step organic salt and fostering a more extensive interaction between PbI₂ and the organic salt. Surprisingly, the oversized residual PbI₂ clusters at the bottom surface of the perovskite layer completely diminish. In addition, advanced depth analysis techniques including depth-resolved grazing-incidence wide-angle X-ray scattering (GIWAXS) and bottom thinning technology are employed for a comprehensive understanding of the reduction in residual PbI₂. Leveraging effective PbI₂ management and regulation of the perovskite crystallization process, the champion devices achieve a power conversion efficiency (PCE) of 25.06% with long-term stability.

In this work, interface reactive sputtering of transparent electrode is reported for fabricating high-performance semitransparent perovskite solar cells (PSCs) and tandem solar cells (TSCs). Finally, high power conversion efficiency (PCE) values of 19.17%, 26.89%, and 24.33% are achieved for a semitransparent PSC, a four-terminal TSC, and a two-terminal TSC, respectively.

Abstract

Sputtered indium tin oxide (ITO) fulfills the requirements of top transparent electrodes (TTEs) in semitransparent perovskite solar cells (PSCs) and stacked tandem solar cells (TSCs), as well as of the recombination layers in monolithic TSCs. However, the high-energy ITO particles will cause damage to the devices. Herein, the interface reactive sputtering strategy is proposed to construct cost-effective TTEs with high transmittance and excellent carrier transporting ability. Polyethylenimine (PEI) is chosen as the interface reactant that can react with sputtered ITO nanoparticles, so that, coordination compounds can be formed during the deposition process, facilitating the carrier transport at the interface of C₆₀/PEI/ITO. Besides, the impact force of energetic ITO particles is greatly alleviated, and the intactness of the underlying C₆₀ layer and perovskite layer is guaranteed. Thus, the prepared semitransparent subcells achieve a significantly enhanced power conversion efficiency (PCE) of 19.17%, surpassing those based on C₆₀/ITO (11.64%). Moreover, the PEI-based devices demonstrate excellent storage stability, which maintains 98% of their original PCEs after 2000 h. On the strength of the interface reactive sputtering ITO electrode, a stacked all-perovskite TSC with a PCE of 26.89% and a monolithic perovskite–organic TSC with a PCE of 24.33% are successfully fabricated.

Publication date: 15 June 2024

Source: Nano Energy, Volume 125

Author(s): Hye Seung Kim, Yongjoon Cho, Heunjeong Lee, Seoyoung Kim, Eui Dae Jung, Young Wook Noh, Sangmi Park, Shinuk Cho, Bo Ram Lee, Changduk Yang, Myoung Hoon Song

Publication date: 15 June 2024

Source: Nano Energy, Volume 125

Author(s): Dou Luo, Lifu Zhang, Jie Zeng, Tingting Dai, Lanqing Li, Wai-Yeung Wong, Baomin Xu, Erjun Zhou, Yiwang Chen, Aung Ko Ko Kyaw

This study explores the impact of blending PTQ8/PTQ10 with Y6 using CGMD. The diminished photovoltaic efficiencies of PTQ8:Y6 blends compared to PTQ10:Y6 blends are not solely attributed to reduced driving forces. The incorporation of fluorine-substituted sites within the PTQ emerges as a significant factor, inducing coiling within PTQ8 and consequently compromising the crystalline structure within the blends.

For bulk-heterojunction organic solar cells (OSCs), molecular structure design to control molecular stacking is crucial to obtain ideally phase-separated morphology and high device performance. Herein, the investigation focuses on two polythiophene-quinoxaline (PTQ) derivatives (PTQ8 and PTQ10) blended with Y6, utilizing coarse-grained molecular dynamics simulations based on the Lennard–Jones static potential (LJSP) method. The study reveals that the diminished photovoltaic efficiencies of PTQ8:Y6 blends, compared to PTQ10:Y6 blends, are not solely attributed to reduced driving forces. The introduction of fluorine-substituted sites in the thiophene group of PTQ polymer is identified as a significant factor. This alteration causes PTQ polymers in PTQ8:Y6 blends to coil, compromising the crystalline structure. PTQ8's bifluorine group induces a repulsive effect on the quinoxaline group, leading to a coiled-chain structure that hinders chain stacking. Conversely, PTQ10 exhibits a straighter chain conformation. Additionally, PTQ8's high solubility in chloroform prevents effective aggregation, further impeding suitable morphology formation. Coarse-grained simulations employing LJSP prove effective in precisely exploring the morphology of OSCs, offering crucial insights for materials in this field.

To address the drawbacks of conventional PEDOT:PSS, NiAc·4H₂O/2PACz is developed as hole transporting layer (HTL). The HTL exhibits distinctive advantages, including an environmentally friendly processability, suitable work function, enhanced hole mobility, improved exciton dissociation efficiency, and minimized recombination loss compared to PEDOT:PSS alternative, ultimately boosting the efficiency and stability of organic solar cells.

Abstract

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.

A novel multifunctional additive 4-Phenylthiosemicarbazide (4PTSC) effectively regulated the crystal growth process in Sn perovskite, strong chemical interactions of 4PTSC with uncoordinated Sn²⁺ eliminated defects, suppressed non-radiative recombinations, and controlled oxidation. Sn wideband gap perovskite solar cells realize the record highest efficiency of 12.22% for the champion device, with low open circuit voltage loss and almost negligible hysteresis.

Abstract

The utilization of wide bandgap (WBG) tin halide perovskites (Sn-HPs) offers an environmentally friendly alternative for multi-junction Sn-HP photovoltaics. Nonetheless, rapid crystallization leads to suboptimal film morphology and substantial creation of defect states, which undermine device efficiency. This study introduces 4-Phenylthiosemicarbazide (4PTSC) as an additive to achieve a densely packed Sn-HP film with fewer imperfections. The strong chemical coordination between SnI₂ and the functional groups S═C─N (Sn···S═C─N), NH₂, and phenyl conjugation enhances solution stability and supports the delay of perovskite crystallization through adduct formation. This process yields pinhole-free films with preferred grain growth. 4PTSC acts as a strong coordination complex and a reducing agent to passivate uncoordinated Sn²⁺ and halide ions and reduce the formation of SnI₄, thereby reducing defect formation. The π-conjugated phenyl ring in the 4PTSC facilitates the preferred crystal growth orientation of perovskite grains. Furthermore, the hydrophobic nature of 4PTSC mitigates Sn²⁺ oxidation by repelling moisture, enhancing stability. The open circuit voltage significantly increased from 0.78 to 0.94 V, resulting in achieving the champion efficiency of 12.22% (certified 11.70%), surpassing all previously reported efficiencies for WBG Sn halide perovskite solar cells. Additionally, the unencapsulated 4PTSC-1.0 device maintained outstanding stability over 1200 h under ambient atmospheric conditions.

The high-thermal tolerance flexible perovskite solar cells with excellent mechanical stability are successfully achieved by a new thermal radiation annealing methodology, which aids in the vertical growth of perovskite grains, reduction of grain boundaries, and decrease of lattice mismatch. These microstructural improvements are essential in enhancing the performance of flexible perovskite photovoltaics.

Abstract

Common polymeric conductive electrodes, such as polyethylene terephthalate (PET) coated with indium tin oxide, face a major challenge due to their low processing-temperature limits, attributed to PET's low glass transition temperature (Tg) of (70–80 °C). This limitation significantly narrows the scope of material selection, limits the processing techniques applicable to the low Tg, and hinders the ripened technology transfer from glass substrates to them. Addressing the temperature constraints of the flexible substrates is impactful yet underexplored, with broader implications for fields beyond photovoltaics. Here, a new thermal radiation annealing methodology is introduced to address this issue. By applying the above Tg radiation annealing in conjunction with thermoelectric cooling, highly ordered molecular packing on PET substrates is successfully created, which is exclusively unachievable due to PET's low thermal tolerance. As a result, in the context of perovskite solar cells, this approach enables the circumvention of high-temperature annealing limitations of PET substrates, leading to a remarkable flexible device efficiency of 22.61% and a record fill factor of 83.42%. This approach proves especially advantageous for advancing the field of flexible optoelectronic devices.

Publication date: 15 May 2024

Source: Joule, Volume 8, Issue 5

Author(s): Baobing Fan, Huanhuan Gao, Yanxun Li, Yiwen Wang, Chaowei Zhao, Francis R. Lin, Alex K.-Y. Jen

For inverted perovskite solar cells, 4,4-difluoropiperidine hydrochloride (2FPD) is applied to form ferroelectric 2D/3D heterojunction with orientated dipoles and defect passivation functionality, which enhances the built-in electric field, delays the cooling process of hot-carriers and achieves efficient charge transport.

Abstract

While the 2D/3D heterojunction is an effective method to improve the power conversion efficiency (PCE) of perovskite solar cells (PSCs), carriers are often confined in the quantum wells (QWs) due to the unique structure of 2D perovskite, which makes the charge transport along the out-of-plane direction difficult. Here, a 2D/3D ferroelectric heterojunction formed by 4,4-difluoropiperidine hydrochloride (2FPD) in inverted PSCs is reported. The enriched 2D perovskite (2FPD)₂PbI₄ layer with n = 1 on the perovskite surface exhibits ferroelectric response and has oriented dipoles along the out-of-plane direction. The ferroelectricity of the oriented dipole layer facilitates the enhancement of the built-in electric field (1.06 V) and the delay of the cooling process of hot carriers, reflected in the high carrier temperature (above 1400 K) and the prolonged photobleach recovery time (139.85 fs, measured at bandgap), improving the out-of-plane conductivity. In addition, the alignment of energy levels is optimized and exciton binding energy (32.8 meV) is reduced by changing the dielectric environment of the surface. Finally, the 2FPD-treated PSCs achieve a PCE of 24.82% (certified: 24.38%) with the synergistic effect of ferroelectricity and defect passivation, while maintaining over 90% of their initial efficiency after 1000 h of maximum power point tracking.

A novel self-assembled monolayer material of 4PADCB as hole transport layer for organic photovoltaics (OPV) is reported to enhance the photon incident and improve the morphology of upper active layer. By incorporating 4PADCB into the binary D18:L8BO OPV, a device efficiency of 19.02% and module efficiency of 15.44% are achieved. The latter represents the highest efficiency of the large-area binary OPV module.

Abstract

Efficient and stable hole transport layer (HTL) is an important component of organic photovoltaics (OPV). Herein, a novel self-assembled monolayer material of 4PADCB (short for (4-(7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid) as HTL for non-fullerene (NF) OPV is reported. Compared to the widely used PEDOT:PSS HTL, the usage of 4PADCB not only enhances photon incident and charge generation but also effectively improves the morphology of the upper active layer, promotes molecular packing, and balances the carrier transport within active layer. As a result, the single-junction binary D18:L8BO OPV, employing 4PADCB as HTL, achieves a high-power conversion efficiency (PCE) of 19.02% with excellent storage stability. Furthermore, a 19.3 cm² OPV module comprising seven sub-cells demonstrates a maximum PCE of 15.44%, which is the highest value of reported efficiency for large-area binary OPV modules. Meanwhile, the module is the first demonstration of an OPV module based on self-assembled monolayer material. This work underscores the substantial potential for the application of 4PADCB in efficient NF OPV devices and high-throughput large-area modules.

The introduction of choline acetate alongside the perovskite precursors triggers the formation of a 1D/3D perovskite heterojunction at the buried interface of the active layer. Due to enhanced homogeneity, defect passivation, and improved interfacial energy alignment, inverted architecture perovskite solar cells reach a maximum photovoltaic efficiency of >24% with improved stability.

Abstract

Interfacial modification is a key strategy for improving the performance of perovskite photovoltaic devices. While the modification of the top surface of the perovskite active layer is well established, engineering of the buried interface is highly challenging. Here, the spontaneous formation of a 1D/3D perovskite heterojunction at the buried interface of a perovskite active layer by incorporating choline acetate alongside the perovskite precursors is reported. Importantly, extensive spectroscopic and microscopic characterization and solid-state nuclear magnetic resonance experiments demonstrate the formation of phase-pure 1D and 3D domains. The 1D/3D junction results in a suppression of the defect states and an improved energetic level alignment at the buried interface, leading to a maximum power conversion efficiency of >24% when incorporated in inverted architecture perovskite solar cells. This work introduces a versatile approach to the modification of the buried interface of the perovskite active layer.

In recent years, self-assembled monolayers (SAMs) have been investigated as a fascinating hole-selective contact for inverted positive-intrinsic-negative (p-i-n) perovskite solar cells (IPSCs). Here, the rapid progress of the IPSCs based on SAMs is comprehensively reviewed from the aspects of efficiency and stability progress, device up-scaling issues, and cost analysis.

Abstract

Inverted positive-intrinsic-negative (p-i-n) perovskite solar cells (IPSCs) have attracted widespread attention due to their low fabrication temperature, good stability in ambient air, and the potential for use in flexible and tandem devices. In recent years, self-assembled monolayers (SAMs) have been investigated as a promising hole-selective contact for IPSCs, leading to an impressive record efficiency of about 26%, which is comparable to that of the regular n-i-p counterparts. This review focuses on the progress of SAM-based IPSCs from the perspective of energy level matching, defect passivation, interface carrier extraction, and SAMs’ stability improvement, as well as the advances in up-scalable fabrication of SAMs and perovskite layers for efficient solar modules and tandem devices. A cost analysis of the SAMs and other commonly used hole-selective materials is conducted to evaluate their cost-effectiveness for photovoltaic applications. Finally, the future challenges are pointed out and the perspectives on how to up-scale SAM-based IPSCs and improve their long-term operational stability are provided.

2D/3D wide-bandgap perovskites are successfully constructed using 1-TzFACl as a spacer. The 2D/3D perovskite exhibits better film quality, enhanced crystallinity, and suppressed nonradiative recombination losses. The optimized device based on 2D/3D perovskite shows an efficiency of 21.58% with enhanced phase stability. An efficiency of 25.66% and improved light stability are achieved for monolithic 2-terminal perovskite/silicon tandem solar cells.

To maximize the power conversion efficiency (PCE) and stability of perovskite/silicon tandem solar cells (TSCs), high-performance and stable perovskite top cells with wide-bandgaps are required. A 2D/3D wide-bandgap perovskite with a bandgap of 1.69 eV using 1H-1,2,4-triazole-1-carboximidamide (1-TzFACl) as a spacer is developed. The 2D/3D wide-bandgap perovskite shows better film quality, enhanced crystallinity, suppressed nonradiative recombination, and significantly improved phase stability. Its initial PCE (21.58%) remains above 87% after 1560 h of continuous illumination due to the insertion of Cl⁻ in the perovskite lattice. A monolithic two-terminal perovskite/silicon TSC achieves a PCE of 25.66% with high light stability. This work provides an ingenious strategy to restrain the phase segregation in wide-bandgap perovskites, leading to effective and stable perovskite/silicon TSCs.