Chen Weijie

Publication date: October 2023

Source: Nano Energy, Volume 115

Author(s): Zhifang Wu, Enbing Bi, Luis K. Ono, Dengbing Li, Osman M. Bakr, Yanfa Yan, Yabing Qi

Introducing the dipolar interlayer has made critical contribution to the fast development of perovskite solar cell (PSC) technology. A systematic overview and deep-going discussion on the working mechanisms of different dipolar interlayers in PSCs is provided. A perspective on how to develop more effective dipolar interlayer materials and further enhancing the device performance is also given.

A typical perovskite solar cell (PSC) is composed of a perovskite layer, electron/hole transport layer(s), cathode, and anode, producing several interfaces between these functional layers. These interfaces undoubtedly have great influence on the device performance. Introducing the dipolar interlayer is one of the most significant interface engineering strategies in PSCs, which helps to improve the charge extraction and collection and has made critical contribution to the fast development of PSC technology. Herein, the progress in the use of dipolar interlayers to promote the performance of PSCs is summarized. The dipolar interlayers in PSCs based on the device structure are categorized and the effect of each type of dipolar interlayer on the interface energy-level structure, interface charge transport and recombination, the interface defect passivation, perovskite morphology, and the device performance is discussed. A perspective on how to develop more effective dipolar interlayer materials and further enhancing the device performance from the viewpoint of the interface and dipolar interlayers is given.

This work classified the connection manners of subcells within a tandem cell into three main categories, focusing on systematical description of intermediate layers using different materials. Useful guidance is provided on how to carry out a suitable intermediate connection in the design of tandem solar cells depending on the selected subcells and device structure.

Abstract

Tandem solar cells are rationally designed and fabricated by stacking multiple subcells to achieve power conversion efficiency well above the Shockley-Queisser (SQ) limit. There is a large selection pool for the subcell candidates, such as Si, III–V, Kesterite, Perovskite, and organic solar cells. A series of different combinations of these subcells have been successfully demonstrated in practical tandem solar cell devices. However, there has not been a systematic summary of how to connect subcells in a tandem solar cell using a practical, cost-effective, and efficiency-beneficial fashion. In this work, the connection manners of subcells within a tandem cell are classified into three main categories, performing sequential growth, using the physical connection, and applying an intermediate layer, focusing on systematical description of intermediate layers using different materials. The advantages and disadvantages of these connection methods and their applicability to tandem cell types are further elaborated using two typical example models, III–V/Si and Perovskite inclusive tandem cell devices. Eventually, this work can provide useful guidance on how to carry out a suitable intermediate connection in the design of tandem solar cells depending on the selected subcells and device structure.

Herein, a sacrificing dye (Rhodamine B isothiocyanate) is developed to improve the quality of perovskite film by in situ release of ethylammonium cations, isothiocyanate anions and benzoic acid molecules. The released ions/molecules can effectively passivate defects and regulate the growth of CsPbI₃ films to obtain the CsPbI₃ solar cells with a champion PCE of 20.95% and high stability.

Abstract

All-inorganic perovskite solar cells (PSCs) have been the research focus due to their high thermal stability and proper band gap for tandem solar cells. However, their power conversion efficiency (PCE) is still lower than that of organic-inorganic hybrid PSCs. Herein, a sacrificing dye (Rhodamine B isothiocyanate, RBITC) is developed to regulate the growth of perovskite film by in situ release of ethylammonium cations, isothiocyanate anions and benzoic acid molecules upon annealing and illumination. The ethylammonium cations can efficiently passivate surface defects. The isothiocyanate anions incorporate with uncoordinated Pb to regulate the crystallization process. The benzoic acid molecules facilitate the nucleation of the perovskite crystals. Especially, the illumination can accelerate the release of these beneficial ions/molecules to improve the quality of perovskite films further. After optimization with RBITC, a high open circuit voltage (V _OC) of 1.24 V and a champion PCE of 20.95% are obtained, which are among the highest Voc and PCE values of CsPbI₃ PSCs. Accordingly, the operational stability of the PSC devices is significantly improved. The results provide an efficient chemical strategy to regulate the formation of perovskite films in whole crystallization process for high performance all-inorganic PSCs.

2D/3D hybrid perovskite have behaved great potential. However, there remains a lack of comprehensive comprehension and systematic summary of the functionality of 2D perovskite attributed to the complex nature of 2D/3D structures. Here, the mechanism underlying the various functions of the 2D phase in 2D/3D structure is carefully examined, hoping to serve as a guide for the development of this field in the future.

Abstract

Organic-inorganic hybrid perovskite solar cells (PSCs) with unique properties exhibit their powerful competitiveness in the photovoltaic field over the past few years. However, the challenges of stability for perovskite devices limit the commercialization and further development. The 2D/3D hybrid structures combine the superior efficiency of bulk perovskites and the superior stability of layered perovskites and gradually get hotspots of the photovoltaic field. In addition, there remains a lack of comprehensive understanding and systematic summary of the function of 2D perovskite attributed to the complex nature of 2D/3D structures. Here, the latest progress of 2D/3D hybrid structures and focus on the functionality of 2D phases in mixed structures and the underlying mechanism from the perspective of their different distributions in the perovskite layer is summarized. Then, the insight and vital factors for overall improvements in the stability of 2D/3D structures are thoroughly discussed. Finally, it is expected that this review will contribute to the present challenges and future research prospects in the photovoltaic industry.

Publication date: 10 October 2023

Source: Electrochimica Acta, Volume 465

Author(s): Antonín Trojánek, Vladimír Mareček, Jan Fiedler, Zdeněk Samec

2D chiral halide perovskites crystallizing in nonpolar enantiomorphic space groups present incomplete Rashba-like splittings of the bottom conduction and top valence bands, resulting in rare spin textures and chirality-induced spin selectivity. The electron's spin polarization in these stable thin films allows the fabrication of chiro-spintronic devices such as spin valves.

Abstract

In the last decade, chirality-induced spin selectivity (CISS), the spin-selective electron transport through chiral molecules, has been described in a large range of materials, from insulators to superconductors. Because more experimental studies are desired for the theoretical understanding of the CISS effect, chiral metal-halide semiconductors may contribute to the field thanks to their chiroptical and spintronic properties. In this regard, this work uses new chiral organic cations S-HP1A and R-HP1A (HP1A = 2-hydroxy-propyl-1-ammonium) to prepare 2D chiral halide perovskites (HPs) which crystallize in the enantiomorphic space groups P4₃2₁2 and P4₁2₁2, respectively. The fourfold symmetry induces antiferroelectricity along the stacking axis which, combined to incomplete Rashba-like splitting in each individual 2D polar layer, results in rare spin textures in the band structure. As revealed by magnetic conductive-probe atomic force microscopy (AFM) measurements, these materials show CISS effect with partial spin polarization (SP; ±40–45%). This incomplete effect is efficient enough to drive a chiro-spintronic device as demonstrated by the fabrication of spin valve devices with magnetoresistance (MR) responses up to 250 K. Therefore, these stable lead–bromide HP materials not only represent interesting candidates for spintronic applications but also reveal the importance of polar symmetry-breaking topology for spin selectivity.

A dual low-temperature approach of halide mixing (replacing I with Br) to increase bandgap and interface modification using tetrabutylammonium bromide (TBAB) to create a low-dimensional perovskite significantly boosts flexible cell performance on polyethylene terephthalate films, reaching a record 32.5% efficiency at 1000 lx under indoor illumination. TBAB treatment reduces defect densities and charge-carrier recombination and improves ambient stability.

Flexible perovskite solar cells are lightweight, bendable, and applicable to curved surfaces. Polyethylene terephthalate (PET) has become the substrate of choice compared to other plastic substrates like polyethylene naphthalate. PET is not only stable but also much cheaper to manufacture, an important factor for photovoltaics (PV). Herein, highly efficient devices on PET are demonstrated using a dual low-temperature (≤100 °C) approach, first by anion mixing (replacing I with Br) of the lead-containing perovskite composition, increasing bandgap (42% improvement), and then by interfacial engineering with tetrabutylammonium bromide (TBAB) (a further 26% improvement), reaching efficiencies of 28.9% at 200 lx and a record 32.5% at 1000 lx. The TBA⁺ cation intercalates into the structure, substituting formamidinium cations at the perovskite/TBAB interface, inducing the formation of large-sized, lower dimensional structures over the 3D perovskite matrix. The resulting PV cell has 1.4 times higher carrier lifetime, one order of magnitude lower leakage currents, and 3 times lower defect densities, suppressing recombination. Importantly, stability (ISOS-D1 protocol) improves by more than double with treatment. Highly efficient and stable cells on PET films enable seamless integration with wearable, portable, smart building, and Internet of Things electronic devices, expanding the reach of indoor applications.

Green-processed organic solar cells based on Y-series electron acceptors have been comprehensively reviewed in this article, focusing on non-halogenated solvents from aromatic, non-aromatic, and water/alcohol solvents for solution-processing photoactive layers. The key problems and the possible way to tackle these issues have also been raised to further improve the photovoltaic performance of this kind of cells.

Abstract

The development of environmentally friendly and sustainable processes for the production of high-performance organic solar cells (OSCs) has become a critical research area. Currently, Y-series electron acceptors are widely used in high-performance OSCs, achieving power conversion efficiencies above 19%. However, these acceptors have large fused conjugated backbones that are well-soluble in halogenated solvents, such as chloroform and chlorobenzene, but have poor solubility in non-halogenated green solvents. To overcome this challenge, recent studies have focused on developing green-processed OSCs that use non-chlorinated and non-aromatic solvents to dissolve bulk-heterojunction photoactive layers based on Y-series electron acceptors, enabling environmentally friendly fabrication. In this comprehensive review, an overview of recent progress in green-processed OSCs based on Y-series acceptors is provided, covering the determination of Hansen solubility parameters, the use of non-chlorinated solvents, and the dispersion of conjugated nanoparticles in water/alcohol. It is hoped that the timely review will inspire researchers to develop new ideas and approaches in this important field, ultimately leading to the practical application of OSCs.

Operando photoluminescence measurements and drift-diffusion simulations are used to investigate the performance of perovskite solar cells with different electron transport materials (ETMs). It is demonstrated that the energetic alignment at the perovskite/ETM interface strongly influences the balance between electronic charge extraction and recombination. Moreover, electronic charge accumulation is observed at short-circuit, which is attributed to field screening by mobile ions.

Abstract

Understanding the kinetic competition between charge extraction and recombination, and how this is impacted by mobile ions, remains a key challenge in perovskite solar cells (PSCs). Here, this issue is addressed by combining operando photoluminescence (PL) measurements, which allow the measurement of real-time PL spectra during current–voltage (J–V) scans under 1-sun equivalent illumination, with the results of drift-diffusion simulations. This operando PL analysis allows direct comparison between the internal performance (recombination currents and quasi-Fermi-level-splitting (QFLS)) and the external performance (J–V) of a PSC during operation. Analyses of four PSCs with different electron transport materials (ETMs) quantify how a deeper ETM LUMO induces greater interfacial recombination, while a shallower LUMO impedes charge extraction. Furthermore, it is found that a low ETM mobility leads to charge accumulation in the perovskite under short-circuit conditions. However, thisalone cannot explain the remarkably high short-circuit QFLS of over 1 eV which is observed in all devices. Instead, drift-diffusion simulations allow this effect to be assigned to the presence of mobile ions which screen the internal electric field at short-circuit and lead to a reduction in the short-circuit current density by over 2 mA cm⁻² in the best device.

Appropriate molecular aggregations are critical to ternary organic solar cells. In this work, a versatile embedded host/guest alloy-like aggregation in the ternary matrix is reported and the primary driving forces to regulate guest distributions are outlined. With optimized molecular packing and exciton/charge properties, exceptional fill factors over 81% are realized from Y6-free ternary devices, and 19.2% efficiencies are recorded based on Y6-family acceptors.

Abstract

The ternary strategy has been intensively studied to improve the power conversion efficiencies of organic photovoltaics. Thereinto, the location of the guest component plays a critical role, but few reports have been devoted to this concern. Hereon, the distribution of LA1 as a guest acceptor in a variety of ternary scenarios is reported and the dominating driving forces of managing the guest distribution and operating modes are outlined. Governed by the appropriate relationship of compatibility, crystallinity, and surface energies between host and guest acceptors, as well as interfacial interactions between donor and dual acceptors, most of the LA1 molecules permeate into the internal of host acceptor phases, forming embedded host/guest alloy-like aggregations. The characteristic distributions greatly optimize the morphologies, maximize energy transfer, and enhance exciton/charge behaviors. Particularly, PM6:IT-4F:LA1 ternary cells afford high efficiency of 15.27% with impressive fill factors (FF) over 81%. The popularization studies further verify the superiority of the LA1-involved alloy structures, and with the Y6-family acceptor as the host component, an outstanding efficiency of 19.17% is received. The results highlight the importance of guest distribution in ternary systems and shed light on the governing factors of distributing the guests in ternary cells.

Effectively managing excess lead iodide is crucial for enhancing perovskite stability. An innovative approach, tailoring functionalized oxo-graphene nanosheets, stabilizes the perovskite structure and improves charge extraction. This leads to a significant boost in power conversion efficiency and long-term stability in inverted (p-i-n) perovskite solar cells, providing a novel perspective on stabilizing photovoltaic devices.

Abstract

Stability issues could prevent lead halide perovskite solar cells (PSCs) from commercialization despite it having a comparable power conversion efficiency (PCE) to silicon solar cells. Overcoming drawbacks affecting their long-term stability is gaining incremental importance. Excess lead iodide (PbI₂) causes perovskite degradation, although it aids in crystal growth and defect passivation. Herein, we synthesized functionalized oxo-graphene nanosheets (Dec-oxoG NSs) to effectively manage the excess PbI₂. Dec-oxoG NSs provide anchoring sites to bind the excess PbI₂ and passivate perovskite grain boundaries, thereby reducing charge recombination loss and significantly boosting the extraction of free electrons. The inclusion of Dec-oxoG NSs leads to a PCE of 23.7 % in inverted (p-i-n) PSCs. The devices retain 93.8 % of their initial efficiency after 1,000 hours of tracking at maximum power points under continuous one-sun illumination and exhibit high stability under thermal and ambient conditions.

A combination of a low/high index optical coupling layer and a 2D photonic-structured antireflection coating, guided by high-throughput optical screening, is designed for semitransparent organic solar cells, achieving simultaneously a record-high power conversion efficiency of 15.2%, a high average visible transmittance of 32%, a high light utilization efficiency of 4.86%, and a favorable color-rendering index of 82.

Abstract

Semitransparent organic solar cells (ST-OSCs) can be made in different colors, allowing light to pass through, and yet absorb enough visible and near-infrared (NIR) light to generate electricity. However, it remains a challenge to achieve high performing ST-OSCs over the two competing indexes of power conversion efficiency (PCE) and average visible transmittance (AVT). This work reports an effort to develop record-performance ST-OSCs using a low/high index optical coupling layer (OCL) and a 2D photonic-structured antireflective (AR) coating. High-throughput optical screening is used to improve the understanding of OCL structure−performance relationships and the predicting of NIR absorption enhancement for ST-OSCs. The concurrent use of a low/high index Na₃AlF₆ (170 nm)/ZnS (110 nm) OCL, identified among about 200 thousand simulated device configurations and a 900 nm pitch-sized 2D photonic-structured AR coating, fabricated using nanoimprint lithography, enables the record-performance ternary PM6:BTP-eC9:L8-BO-based ST-OSCs, achieving simultaneously a record-high PCE of 15.2%, a high AVT of 32%, an impressive light utilization efficiency of 4.86%, and a favorable color-rendering index of 82. The results of the ST-OSCs demonstrated in this work provide an attractive option for a plethora of applications in self-powered greenhouses and building-integrated photovoltaic systems.

This work presents a synergy between machine learning (ML) materials design and automated perovskite solar cells (PSCs) fabrication. The new bespoke ML algorithm and design of experiment concept provide insights for realization of new highly efficient perovskite materials using robotics and drop-casting, yielding one of the highest performing recorded Ruddlesden–Popper PSCs.

Abstract

Organic–inorganic perovskite solar cells (PSCs) are promising candidates for next-generation, inexpensive solar panels due to their commercially competitive cost and high power conversion efficiencies. However, PSCs suffer from poor stability. A new and vast subset of PSCs, quasi-two-dimensional Ruddlesden–Popper PSCs (quasi-2D RP PSCs), has improved photostability and superior resilience to environmental conditions compared to three-dimensional metal-halide PSCs. To accelerate the search for new quasi-2D RP PSCs, this work reports a combinatorial, machine learning (ML) enhanced high-throughput perovskite film fabrication and optimization study. This work designs a bespoke experimental strategy and produces perovskite films with a range of different compositions using only spin-coating free, reproducible robotic fabrication processes. The performance and characterization data of these solar cells are used to train a ML model that allow materials parameters to be optimized and direct the design of improved materials. The new, ML-optimized, drop-cast quasi-2D RP perovskite films yield solar cells with power conversion efficiencies of up to 16.9%.

Nature Energy, Published online: 31 July 2023; doi:10.1038/s41560-023-01310-y

This work provides a deep understanding of the reason for complicated intermediates in vacuum-assisted blade-coated wide-bandgap (WBG) perovskites. Based on understanding of intermediate formation, additive engineering is applied and (100) single-orientation WBG perovskite films can be successfully obtained. Power conversion efficiency of 16.75% is delivered by vacuum-assisted blade-coated perovskite solar cells, which is the highest value of 1.77 eV perovskites.

Large-scale all-perovskite tandem photovoltaic has raised more attention as the power conversion efficiency (PCE) of this device in a small area reaches 28%. However, the wide-bandgap (WBG)-perovskite (Cs_0.2FA_0.8Pb(I_0.6Br_0.4)₃-1.77 eV) fabrication on a large scale still faces difficulty in nucleation and crystallization control, leading to complicated intermediates and poor-quality films. Through a systematic investigation of the vacuum-assisted blade-coated WBG perovskite film formation process, the origin for poor film quality is attributed to the numerous nucleation pathways under rapid vacuum pressure decrease, resulting in a mix in intermediates of (Cs,FA)₂Pb₃(I,Br)₈·xNMP, δ-FAPbI₃·xNMP, and PbI₂·xNMP. To solve this problem, a proper additive MACl is selected and added. By lowering the formation energy of intermediate ((Cs,FA)Pb(I,Br)₃·MACl·xNMP), the nucleation and crystallization process is successfully modulated into a single way, resulting in a single-orientation (100) film and an enhanced device performance of 16.75%, which is the champion PCE of blade-coated 1.77 eV perovskite so far.

Ternary strategy plays a significant important role in enhancing the performance of organic solar cells (OSCs), which leads to higher light absorption intensity, effective exciton dissociation, charge transport, and collection. With IDIC as the third component, ternary OSCs can be improved in both J _SC and fill factor (FF) with a remarkable power conversion efficiency (PCE) of 18.9%.

Abstract

In this study, using PM6:L8-BO as the main system and non-fullerene acceptor IDIC as the third component, a series of ternary organic solar cells (TOSCs) are fabricated. The results reveal that IDIC plays a significant role in enhancing the performance of TOSCs by optimizing the morphology of blended films and forming interpenetrating nanostructure. The improved film morphology facilitates exciton dissociation and collection in TOSCs, which causes an increase in the short-circuit current density (J _SC) and fill factor (FF). Further, by optimizing the IDIC content, the power conversion efficiency (PCE) of TOSCs reaches 18.9%. Besides, the prepared TOSCs exhibit a J _SC of 27.51 mA cm⁻² and FF of 76.64%, which are much higher than those of PM6:L8-BO-based organic solar cells (OSCs). Furthermore, the addition of IDIC improves the long-term stability of the OSCs. Meanwhile, TOSCs with a large effective area of 1.00 cm² have been prepared, which exhibit a PCE of 12.4%. These findings suggest that modifying the amount of the third component can be a useful strategy to construct hight-efficiency TOSCs with practical application potential.

H-Shaped pentafulvalene-fused hole-transport materials is designed and applied for high performance perovskite solar cells (PSCs). The fluorine-substituted YSH-oF-based PSCs afford the impressive power conversion efficiency of 23.59% and 21.89% for aperture areas of 0.09 and 1.00 cm², respectively.

Abstract

Organic small molecular materials with coplanar π-conjugated system as HTMs in perovskite solar cells (PSCs) have attracted considerable attention due to their high charge transport capability and thermal stability. Herein, three novel pentafulvalene-fused derivatives with or without fluorine atoms incorporated (YSH-oF and YSH-mF and YSH-H, respectively) are designed, synthesized, and applied as hole-transporting materials (HTMs) in PSCs fabrication. The fluorinated HTMs, YSH-oF and YSH-mF, exhibited higher hole mobility and better charge extraction at the perovskite/HTM interface than non-fluorinated one do, presumably due to the closer intermolecular π–π packing interactions. As a result, small-area (0.09 cm²) PSCs made with YSH-oF and YSH-mF achieved an impressive power conversion efficiency (PCE) of 23.59% and 22.76% respectively, with negligible hysteresis, in contrast with the 20.57% for the YSH-H-based devices. Furthermore, for large-area (1.00 cm²) devices, the PSCs employing YSH-oF exhibited a PCE of 21.92%. Moreover, excellent long-term device stability is demonstrated for PSCs with F-substituted HTMs (YSH-oF and YSH-mF), presumably due to the higher hydrophobicity. This study shows the great potential of fluorinated pentafulvalene-fused materials as low-cost HTM for efficient and stable PSCs.

The incorporation of an atomic layer deposited AlO _x layer onto octylammonium iodide promotes the formation of a 2D perovskite layer in response to light, which substantially enhances the performance of the devices, surpassing a power conversion efficiency of 24%. Furthermore, the devices exhibit remarkable light stability, exhibiting minimal degradation when subjected to continuous light illumination under maximum power point tracking.

Abstract

Long-chain organic halide salts are widely used in perovskite-based optoelectronic devices for surface passivation owing to their capability to interact with the surface defects of perovskites. Here, aluminum oxide (AlO _x ) is introduced via atomic layer deposition onto octylammonium iodide (OAI) to exploit the benefits of organic halide salts without generating undesired defects. The devices incorporating AlO _x on OAI-treated perovskite (OAI/AlO _x ) show enhancement in both device performance and photo-stability compared to those with only treatment. A diffusion of aluminum from AlO _x into the perovskite through surface characterization contributes to a uniform photo-generated carrier transport in both the surface and the bulk of the perovskite absorber. In addition, it is revealed that light-induced two-dimensional perovskite formation on OAI/AlO _x . This may be ascribed to preventing the loss of OA cations due to the presence of AlO _x , leading to a decrease in the number of iodine anions which suppresses the light-induced degradation of corresponding devices. Consequently, the devices show over 24% efficiency and retain their efficiency over 1000 hours under continuous light illumination.

Here, a macrocyclic material valinomycin (VM) with multiple ─C═O, ─NH, and ─O─ groups is utilized to manage charged defects by passivating uncoordinated Pb²⁺ and compensating formamidine vacancy at perovskite surface. VM modification also induces a favorable energy band bending. These advances boost the power conversion efficiency from 21.97% to 24.06% for inverted perovskite solar cells.

Abstract

The unavoidably positively and negatively charged defects at the interface between perovskite and electron transport layer (ETL) often lead to severe surface recombination and unfavorable energy level alignment in inverted perovskite solar cells (PerSCs). Inserting interlayers at this interface is an effective approach to eliminate charged defects. Herein, the macrocyclic molecule valinomycin (VM) with multiple active sites of ─C═O, ─NH, and ─O─ is employed as an interlayer at the perovskite/ETL contact to simultaneously eliminate positively and negatively charged defects. Combined with a series of theoretical calculations and experimental analyzes, it is demonstrated that the ─C═O and ─O─ groups in VM can immobilize the uncoordinated Pb²⁺ to manage the positively charged defect and the formation of N─H···I hydrogen bonding can recompense the formamidine vacancies to eliminate the negatively charged defect. In addition, the VM interlayer induces a favorable downshift band bending at the perovskite/ETL interface, facilitating charge separation and boosting charge transfer. Thanks to the reduced charged defects and favorable energy level alignment, the fabricated inverted PerSC delivers an outstanding power conversion efficiency of 24.06% with excellent long-term ambient and thermal stability. This work demonstrates that managing charged defects via multiple functional groups and simultaneously regulating energy level alignment is a reliable strategy to boost the performance of PerSCs.

Publication date: 20 September 2023

Source: Joule, Volume 7, Issue 9

Author(s): Guoping Li, Fei Qin, Robert M. Jacobberger, Subhrangsu Mukherjee, Leighton O. Jones, Ryan M. Young, Robert M. Pankow, Brendan P. Kerwin, Lucas Q. Flagg, Ding Zheng, Liang-Wen Feng, Kevin L. Kohlstedt, Vinod K. Sangwan, Mark C. Hersam, George C. Schatz, Dean M. DeLongchamp, Michael R. Wasielewski, Yinhua Zhou, Antonio Facchetti, Tobin J. Marks

Herein, electro- and photoluminescence imaging is combined with illuminated lock-in thermography (ILIT) for a comprehensive electro-optical characterization of perovskite silicon tandem devices with state-of-the-art cell architecture. The combination of these measurements together with the numerical simulation models Quokka3 and Sentaurus TCAD enables to carry out holistic investigations of device limitations.

The top cell of a perovskite silicon tandem solar cell requires several material layers on each side of the perovskite absorber to efficiently extract electrons and holes, respectively. These layers must meet multiple requirements simultaneously, namely, low interface recombination, good charge carrier selectivity, low contact resistivity, and high optical transparency. Due to the complex architecture, characterization techniques are required in material and process optimization to identify loss mechanisms. Spatial resolution of the characterization is gaining importance along with the upscaling of the perovskite technology. Herein, electro- and photoluminescence (EL and PL) imaging is combined with illuminated lock-in thermography (ILIT) for a comprehensive electro-optical characterization of both subcells in perovskite silicon tandem devices with state-of-the-art cell architecture. Thereby, the combination of the presented characterization methods together with numerical simulation models enables to carry out holistic investigations of device limitations. The strength of this approach is showcased by one particularly remarkable feature that is observed in the investigated tandem device, showing a low PL but high EL signal at local spots. Together with multidimensional optoelectrical device simulations, the measurements are explained and the root cause of this feature to originate from the perovskite/C₆₀ interface is suggested.

An acceptor CH-ThCl featuring an extended conjugated central core dichlorodithienoquinoxaline is designed. An efficiency of 18.80% is achieved for the CH-ThCl-based ternary devices by reducing nonradiative energy loss and tuning active layer morphology.

Abstract

The efficiency of organic solar cells (OSCs) is primarily limited by their significant nonradiative energy loss and unfavorable active layer morphology. Achieving high-efficiency OSCs by suppressing nonradiative energy loss and tuning the active layer morphology remains a challenging task. In this study, an acceptor named CH-ThCl is designed, featuring an extended conjugation central core, dichlorodithienoquinoxaline. The incorporation of chlorine-substituted extended conjugation in the central core enhances the acceptor's rigidity and promotes J-aggregation, leading to improved molecular luminescent efficiency and a reduction in nonradiative energy loss. A binary device based on PM6: CH-ThCl demonstrates a power conversion efficiency (PCE) of 18.16% and exhibits a high open-circuit voltage (V _oc) of 0.934 V, attributed to the remarkably low nonradiative energy loss of 0.21 eV. Furthermore, a ternary device is fabricated by incorporating CH-6F as the third component, resulting in a significantly enhanced PCE of 18.80%. The ternary device exhibits improvements in short-circuit current (J _sc) and fill factor (FF) while maintaining the V _oc, primarily due to the optimized active layer morphology. These results highlight the effectiveness of combining the reduction of nonradiative energy loss and precise tuning of the active layer morphology as a viable strategy for achieving high-efficiency OSCs.

Nature Energy, Published online: 27 July 2023; doi:10.1038/s41560-023-01309-5