Formerly the "Solar and Photovoltaic Engineering Research Center (SPERC)"

Recent Submissions

  • Low-Defect, High Molecular Weight Indacenodithiophene (IDT) Polymers Via a C–H Activation: Evaluation of a Simpler and Greener Approach to Organic Electronic Materials

    Ponder, James F.; Chen, Hung-Yang; Luci, Alexander M. T.; Moro, Stefania; Turano, Marco; Hobson, Archie L.; Collier, Graham S.; Perdigão, Luís M. A.; Moser, Maximilian; Zhang, Weimin; Costantini, Giovanni; Reynolds, John R.; McCulloch, Iain (ACS Materials Letters, American Chemical Society (ACS), 2021-09-16) [Article]
    The development, optimization, and assessment of new methods for the preparation of conjugated materials is key to the continued progress of organic electronics. Direct C–H activation methods have emerged and developed over the last 10 years to become an invaluable synthetic tool for the preparation of conjugated polymers for both redox-active and solid-state applications. Here, we evaluate direct (hetero)arylation polymerization (DHAP) methods for the synthesis of indaceno[1,2-b:5,6-b′]dithiophene-based polymers. We demonstrate, using a range of techniques, including direct visualization of individual polymer chains via high-resolution scanning tunneling microscopy, that DHAP can produce polymers with a high degree of regularity and purity that subsequently perform in organic thin-film transistors comparably to those made by other cross-coupling polymerizations that require increased synthetic complexity. Ultimately, this work results in an improved atom economy by reducing the number of synthetic steps to access high-performance molecular and polymeric materials.
  • Research data supporting "High-mobility, trap-free charge transport in conjugated polymer diodes"

    Nikolka, Mark; Broch, Katharina; Armitage, John; Hanifi, David; Nowack, Peer J.; Venkateshvaran, Deepak; Sadhanala, Aditya; Saska, Jan; Mascal, Mark; Jung, Seok-Heon; Lee, Jin-Kyun; McCulloch, Iain; Salleo, Alberto; Sirringhaus, Henning (Apollo - University of Cambridge Repository, 2021-09-14) [Dataset]
    Origin project including all source data used for Figures 1 to 5.The Project is structured in sub-folders, with one folder dedicated to a specfic Figure of the paper. Folder 1 includes SCLC diode characteristics measured for DPP-BTz SCLC diodes with and without additives. Folder 2 includes low-temperature measurements of diodes, extracted activation energies as well as dn/DE values extracted by SCLC-spectroscopy. Folder 3 includes measured diode characteristics of IDT-BT, MEH:PPV and DPP-DTT SCLC diodes, corresponding dn/dE values and PDS spectroscopy data for these materials. The last Folder includes stability measuremtns of DPP-BTz diodes showing the evolution over 10k IV-characteristics. Any additional data from the paper (such as thoese shown in the SI or GIWAXs data) is available on request. Format
  • An Aqueous Mg 2+ -Based Dual-Ion Battery with High Power Density

    Zhu, Yunpei; Yin, Jun; Emwas, Abdul-Hamid; Mohammed, Omar F.; Alshareef, Husam N. (Advanced Functional Materials, Wiley, 2021-09-13) [Article]
    Rechargeable Mg batteries promise low-cost, safe, and high-energy alternatives to Li-ion batteries. However, the high polarization strength of Mg2+ leads to its strong interaction with electrode materials and electrolyte molecules, resulting in sluggish Mg2+ dissociation and diffusion as well as insufficient power density and cycling stability. Here an aqueous Mg2+-based dual-ion battery is reported to bypass the penalties of slow dissociation and solid-state diffusion. This battery chemistry utilizes fast redox reactions on the polymer electrodes, i.e., anion (de)doping on the polyaniline (PANI) cathode and (de)enolization upon incorporating Mg2+ on the polyimide anode. The kinetically favored and stable electrodes depend on designing a saturated aqueous electrolyte of 4.5 m Mg(NO3)2. The concentrated electrolyte suppresses the irreversible deprotonation reaction of the PANI cathode to enable excellent stability (a lifespan of over 10 000 cycles) and rate performance (33% capacity retention at 500 C) and avoids the anodic parasitic reaction of nitrate reduction to deliver the stable polyimide anode (86.2% capacity retention after 6000 cycles). The resultant full Mg2+-based dual-ion battery shows a high specific power of 10 826 W kg−1, competitive with electrochemical supercapacitors. The electrolyte and electrode chemistries elucidated in this study provide an alternative approach to developing better-performing Mg-based batteries.
  • Design of experiment optimization of aligned polymer thermoelectrics doped by ion-exchange

    Huang, Yuxuan; Lukito Tjhe, Dionisius Hardjo; Jacobs, Ian; Jiao, Xuechen; He, Qiao; Statz, Martin; Ren, Xinglong; Huang, Xinyi; McCulloch, Iain; Heeney, Martin; McNeill, Christopher R.; Sirringhaus, Henning (Applied Physics Letters, AIP Publishing, 2021-09-13) [Article]
    Organic thermoelectrics offer the potential to deliver flexible, low-cost devices that can directly convert heat to electricity. Previous studies have reported high conductivity and thermoelectric power factor in the conjugated polymer poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT). Here, we investigate the thermoelectric properties of PBTTT films in which the polymer chains were aligned uniaxially by mechanical rubbing, and the films were doped by a recently developed ion exchange technique that provides a choice over the counterions incorporated into the film, allowing for more optimized morphology and better stability than conventional charge transfer doping. To optimize the polymer alignment process, we took advantage of two Design of Experiment (DOE) techniques: regular two-level factorial design and central composite design. Rubbing temperature Trub and post-alignment annealing temperature Tanneal were the two factors that were most strongly correlated with conductivity. We were able to achieve high polymer alignment with a dichroic ratio >15 and high electrical conductivities of up to 4345 S/cm for transport parallel to the polymer chains, demonstrating that the ion exchange method can achieve conductivities comparable/higher than conventional charge transfer doping. While the conductivity of aligned films increased by a factor of 4 compared to unaligned films, the Seebeck coefficient (S) remained nearly unchanged. The combination of DOE methodology, high-temperature rubbing, and ion exchange doping provides a systematic, controllable strategy to tune structure–thermoelectric property relationships in semiconducting polymers
  • Interfacial Model Deciphering High-Voltage Electrolytes for High Energy Density, High Safety, and Fast-Charging Lithium-Ion Batteries

    Zou, Yeguo; Cao, Zhen; Zhang, Junli; Wahyudi, Wandi; Wu, Yingqiang; Liu, Gang; Li, Qian; Cheng, Haoran; Zhang, Dongyu; Park, Geon-Tae; Cavallo, Luigi; Anthopoulos, Thomas D.; Wang, Limin; Sun, Yang-Kook; Ming, Jun (Advanced Materials, Wiley, 2021-09-12) [Article]
    High-voltage lithium-ion batteries (LIBs) enabled by high-voltage electrolytes can effectively boost energy density and power density, which are critical requirements to achieve long travel distances, fast-charging, and reliable safety performance for electric vehicles. However, operating these batteries beyond the typical conditions of LIBs (4.3 V vs Li/Li+) leads to severe electrolyte decomposition, while interfacial side reactions remain elusive. These critical issues have become a bottleneck for developing electrolytes for applications in extreme conditions. Herein, an additive-free electrolyte is presented that affords high stability at high voltage (4.5 V vs Li/Li+), lithium-dendrite-free features upon fast-charging operations (e.g., 162 mAh g−1 at 3 C), and superior long-term battery performance at low temperature. More importantly, a new solvation structure-related interfacial model is presented, incorporating molecular-scale interactions between the lithium-ion, anion, and solvents at the electrolyte–electrode interfaces to help interpret battery performance. This report is a pioneering study that explores the dynamic mutual-interaction interfacial behaviors on the lithium layered oxide cathode and graphite anode simultaneously in the battery. This interfacial model enables new insights into electrode performances that differ from the known solid electrolyte interphase approach to be revealed, and sets new guidelines for the design of versatile electrolytes for metal-ion batteries.
  • 3-D Modeling of Ultrathin Solar Cells with Nanostructured Dielectric Passivation: Case Study of Chalcogenide Solar Cells

    Raja, Waseem; Aydin, Erkan; Allen, Thomas; De Wolf, Stefaan (Advanced Theory and Simulations, Wiley, 2021-09-09) [Article]
    Ultrathin solar cells can be a path forward to low-cost photovoltaics due to their reduced material consumption and shorter required deposition times. With excellent surface passivation, such devices may feature higher open-circuit voltages (VOC). However, their short-circuit current density (JSC) may be reduced due to decreased light absorption. This mandates implementation of efficient light-trapping structures. To design efficient ultrathin solar cells that combine surface-passivation and light-trapping features, accurate 3-D modeling is necessary. To this end, a novel 3-D optoelectrical finite-element model is developed to analyze the performance of ultrathin solar cells. The model is applied to the case of ultrathin (<500 nm) chalcogenide solar cells (copper indium gallium (di) selenide, CIGSe), rear-passivated with nanostructured Al2O3 to circumvent optical and electrical losses. It is found that such a nanopatterned dielectric passivation scheme enhances broadband light-trapping with reduced rear-surface recombination, resulting in an absolute power conversion efficiency enhancement of 3.9%, compared to cells without passivation structure. Overall, the work shows how 3-D finite element modeling can aid in analyzing and developing new optical and electrical solar cell designs for ultrathin solar cells such as those based on chalcogenides and perovskites.
  • Redox-Active Polymers Designed for the Circular Economy of Energy Storage Devices

    Tan, Siew Ting Melissa; Quill, Tyler J.; Moser, Maximilian; LeCroy, Garrett; Chen, Xingxing; Wu, Yilei; Takacs, Christopher J.; Salleo, Alberto; Giovannitti, Alexander (ACS Energy Letters, American Chemical Society (ACS), 2021-09-08) [Article]
    Electrochemical energy storage is a keystone to support the rapid transition to a low-carbon-emission future for grid storage and transportation. While research on electrochemical energy storage devices has mostly dealt with performance improvements (energy density and power density), little attention has been paid to designing devices that can be recycled with low cost and low environmental impact. Thus, next-generation energy storage devices should also address the integration of recyclability into the device design. Here, we demonstrate recyclable energy storage devices based on solution-processable redox-active conjugated polymers. The high electronic and ionic charge transport in these polymers enables the operation of single-phase electrodes in aqueous electrolytes with C-rates >100 with good electrochemical stability when the cell is charged to 1.2 V. Finally, we demonstrate the recyclability of these devices, achieving >85% capacity retention in each recycling step. Our work provides a framework for developing recyclable devices for sustainable energy storage technologies.
  • Ambipolar inverters based on cofacial vertical organic electrochemical transistor pairs for biosignal amplification

    Rashid, Reem B.; du, weiyuan; Griggs, Sophie; Maria, Iuliana P.; McCulloch, Iain; Rivnay, Jonathan (Science Advances, American Association for the Advancement of Science (AAAS), 2021-09-08) [Article]
    On-site signal amplification for bioelectronic sensing is a desirable approach to improving recorded signal quality and to reducing the burden on signal transmission and back-end electronics. While organic electrochemical transistors (OECTs) have been used as local transducers of bioelectronic signals, their current output presents challenges for implementation. OECT-based circuits offer new opportunities for high-performance signal processing. In this work, we introduce an active sensing node based on cofacial vertical OECTs forming an ambipolar complementary inverter. The inverter, which shows a voltage gain of 28, is composed of two OECTs on opposite side walls of a single active area, resulting in a footprint identical to a planar OECT. The inverter is used as an analog voltage preamplifier for recording electrocardiogram signals when biased at the input voltage corresponding to peak gain. We further demonstrate compatibility with nontraditional fabrication methods with potential benefits for rapid prototyping and large-area printed electronics.
  • Using Two Compatible Donor Polymers Boosts the Efficiency of Ternary Organic Solar Cells to 17.7%

    Peng, Wenhong; Lin, Yuanbao; Jeong, Sang Young; Firdaus, Yuliar; Genene, Zewdneh; Nikitaras, Aggelos; Tsetseris, Leonidas; Woo, Han Young; Zhu, Weiguo; Anthopoulos, Thomas D.; Wang, Ergang (Chemistry of Materials, American Chemical Society (ACS), 2021-09-07) [Article]
    The use of ternary organic semiconducting blends is recognized as an effective strategy to boost the performance of polymer solar cells (PSCs) by increasing the photocurrent while minimizing voltage losses. Yet, the scarcity of suitable donors with a deep highest occupied molecular orbital (HOMO) level poses a challenge in extending this strategy to ternary systems based on two polymers. Here, we address this challenge by the synthesis of a new donor polymer (PM7-Si), which is akin to the well-known PM6 but has a deeper HOMO level. PM7-Si is utilized as the third component to enhance the performance of the best-in-class binary system of PM6:BTP-eC9, leading to simultaneous improvements in the efficiency (17.7%), open-circuit voltage (0.864 V), and fill factor (77.6%). These decisively enhanced features are attributed to the efficient carrier transport, improved stacking order, and morphology. Our results highlight the use of two polymer donors as a promising strategy toward high-performance ternary PSCs.
  • Linked Nickel Oxide/Perovskite Interface Passivation for High-Performance Textured Monolithic Tandem Solar Cells

    Zhumagali, Shynggys; Isikgor, Furkan Halis; Maity, Partha; Yin, Jun; Ugur, Esma; de Bastiani, Michele; Subbiah, Anand Selvin; Mirabelli, Alessandro James; Azmi, Randi; Harrison, George T.; Troughton, Joel; Aydin, Erkan; Liu, Jiang; Allen, Thomas; Rehman, Atteq Ur; Baran, Derya; Mohammed, Omar F.; De Wolf, Stefaan (Advanced Energy Materials, Wiley, 2021-09-05) [Article]
    Sputtered nickel oxide (NiOx) is an attractive hole-transport layer for efficient, stable, and large-area p-i-n metal-halide perovskite solar cells (PSCs). However, surface traps and undesirable chemical reactions at the NiOx/perovskite interface are limiting the performance of NiOx-based PSCs. To address these issues simultaneously, an efficient NiOx/perovskite interface passivation strategy by using an organometallic dye molecule (N719) is reported. This molecule concurrently passivates NiOx and perovskite surface traps, and facilitates charge transport. Consequently, the power conversion efficiency (PCE) of single-junction p-i-n PSCs increases from 17.3% to 20.4% (the highest reported value for sputtered-NiOx based PSCs). Notably, the N719 molecule self-anchors and conformally covers NiOx films deposited on complex surfaces. This enables highly efficient textured monolithic p-i-n perovskite/silicon tandem solar cells, reaching PCEs up to 26.2% (23.5% without dye passivation) with a high processing yield. The N719 layer also forms a barrier that prevents undesirable chemical reactions at the NiOx/perovskite interface, significantly improving device stability. These findings provide critical insights for improved passivation of the NiOx/perovskite interface, and the fabrication of highly efficient, robust, and large-area perovskite-based optoelectronic devices.
  • Understanding the Charge Transfer State and Energy Loss Trade-offs in Non-fullerene-Based Organic Solar Cells

    Peña, Top Archie Dela; Khan, Jafar Iqbal; Chaturvedi, Neha; Ma, Ruijie; Xing, Zengshan; Gorenflot, Julien; Sharma, Anirudh; Ng, Fai Lun; Baran, Derya; Yan, He; Laquai, Frédéric; Wong, Kam Sing (ACS Energy Letters, American Chemical Society (ACS), 2021-09-03) [Article]
    Energy losses significantly reduce the open-circuit voltage among current state-of-the-art organic solar cells (OSCs), which limits the further enhancement of their power conversion efficiencies (PCEs). In this study, the bulk heterojunction blends of PM6 donor and halogenated nonfullerene acceptors (NFAs) display a trade-off between radiative energy losses, i.e., charge transfer state (CTS) radiative energy loss (ΔErad) and the loss associated with CTS formation from acceptor singlet excitons (ΔECTEL). Similarly, a trade-off between ΔErad and the nonradiative energy loss (ΔEnr) is found, reflecting a competition in radiative and nonradiative charge recombination pathways. Further, the energy levels of relaxed CTS (ECTEL) are shown to exhibit dependence on morphologically induced energetic traps, suggesting that it should not be associated merely to blend constituents. Interestingly, these correlations extend even to thermally degraded devices considered herein. Accordingly, this work provides further understandings of energy losses relevant to overcome the current limitations concerning NFA-based OSC developments.
  • There is plenty of room at the top: generation of hot charge carriers and their applications in perovskite and other semiconductor-based optoelectronic devices.

    Ahmed, Irfan; Shi, Lei; Pasanen, Hannu; Vivo, Paola; Maity, Partha; Hatamvand, Mohammad; Zhan, Yiqiang (Light, science & applications, Springer Science and Business Media LLC, 2021-09-01) [Article]
    Hot charge carriers (HC) are photoexcited electrons and holes that exist in nonequilibrium high-energy states of photoactive materials. Prolonged cooling time and rapid extraction are the current challenges for the development of future innovative HC-based optoelectronic devices, such as HC solar cells (HCSCs), hot energy transistors (HETs), HC photocatalytic reactors, and lasing devices. Based on a thorough analysis of the basic mechanisms of HC generation, thermalization, and cooling dynamics, this review outlines the various possible strategies to delay the HC cooling as well as to speed up their extraction. Various materials with slow cooling behavior, including perovskites and other semiconductors, are thoroughly presented. In addition, the opportunities for the generation of plasmon-induced HC through surface plasmon resonance and their technological applications in hybrid nanostructures are discussed in detail. By judiciously designing the plasmonic nanostructures, the light coupling into the photoactive layer and its optical absorption can be greatly enhanced as well as the successful conversion of incident photons to HC with tunable energies can also be realized. Finally, the future outlook of HC in optoelectronics is highlighted which will provide great insight to the research community.
  • Reversible Electrochemical Charging of n-Type Conjugated Polymer Electrodes in Aqueous Electrolytes

    Szumska, Anna A.; Maria, Iuliana P.; Flagg, Lucas Q.; Savva, Achilleas; Surgailis, Jokubas; Paulsen, Bryan D.; Moia, Davide; Chen, Xingxing; Griggs, Sophie; Mefford, J. Tyler; Rashid, Reem B.; Marks, Adam; Inal, Sahika; Ginger, David S.; Giovannitti, Alexander; Nelson, Jenny (Journal of the American Chemical Society, American Chemical Society (ACS), 2021-09-01) [Article]
    Conjugated polymers achieve redox activity in electrochemical devices by combining redox-active, electronically conducting backbones with ion-transporting side chains that can be tuned for different electrolytes. In aqueous electrolytes, redox activity can be accomplished by attaching hydrophilic side chains to the polymer backbone, which enables ionic transport and allows volumetric charging of polymer electrodes. While this approach has been beneficial for achieving fast electrochemical charging in aqueous solutions, little is known about the relationship between water uptake by the polymers during electrochemical charging and the stability and redox potentials of the electrodes, particularly for electron-transporting conjugated polymers. We find that excessive water uptake during the electrochemical charging of polymer electrodes harms the reversibility of electrochemical processes and results in irreversible swelling of the polymer. We show that small changes of the side chain composition can significantly increase the reversibility of the redox behavior of the materials in aqueous electrolytes, improving the capacity of the polymer by more than one order of magnitude. Finally, we show that tuning the local environment of the redox-active polymer by attaching hydrophilic side chains can help to reach high fractions of the theoretical capacity for single-phase electrodes in aqueous electrolytes. Our work shows the importance of chemical design strategies for achieving high electrochemical stability for conjugated polymers in aqueous electrolytes.
  • High-Efficiency Ion-Exchange Doping of Conducting Polymers

    Jacobs, Ian E.; Lin, Yue; Huang, Yuxuan; Ren, Xinglong; Simatos, Dimitrios; Chen, Chen; Tjhe, Dion; Statz, Martin; Lai, Lianglun; Finn, Peter A.; Neal, William G.; D'Avino, Gabriele; Lemaur, Vincent; Fratini, Simone; Beljonne, David; Strzalka, Joseph; Nielsen, Christian B.; Barlow, Stephen; Marder, Seth R.; McCulloch, Iain; Sirringhaus, Henning (Advanced Materials, Wiley, 2021-08-21) [Article]
    Molecular doping—the use of redox-active small molecules as dopants for organic semiconductors—has seen a surge in research interest driven by emerging applications in sensing, bioelectronics, and thermoelectrics. However, molecular doping carries with it several intrinsic problems stemming directly from the redox-active character of these materials. A recent breakthrough was a doping technique based on ion-exchange, which separates the redox and charge compensation steps of the doping process. Here, the equilibrium and kinetics of ion exchange doping in a model system, poly(2,5-bis(3-alkylthiophen-2-yl)thieno(3,2-b)thiophene) (PBTTT) doped with FeCl3 and an ionic liquid, is studied, reaching conductivities in excess of 1000 S cm−1 and ion exchange efficiencies above 99%. Several factors that enable such high performance, including the choice of acetonitrile as the doping solvent, which largely eliminates electrolyte association effects and dramatically increases the doping strength of FeCl3, are demonstrated. In this high ion exchange efficiency regime, a simple connection between electrochemical doping and ion exchange is illustrated, and it is shown that the performance and stability of highly doped PBTTT is ultimately limited by intrinsically poor stability at high redox potential.
  • Ion Pair Uptake in Ion Gel Devices Based on Organic Mixed Ionic–Electronic Conductors

    Quill, Tyler J.; LeCroy, Garrett; Melianas, Armantas; Rawlings, Dakota; Thiburce, Quentin; Sheelamanthula, Rajendar; Cheng, Christina; Tuchman, Yaakov; Keene, S. T.; McCulloch, Iain; Segalman, Rachel A.; Chabinyc, Michael L; Salleo, Alberto (Advanced Functional Materials, Wiley, 2021-08-21) [Article]
    In organic mixed ionic–electronic conductors (OMIECs), it is critical to understand the motion of ions in the electrolyte and OMIEC. Generally, the focus is on the movement of net charge during gating, and the motion of neutral anion–cation pairs is seldom considered. Uptake of mobile ion pairs by the semiconductor before electrochemical gating (passive uptake) can be advantageous as this can improve device speed, and both ions can participate in charge compensation during gating. Here, such passive ion pair uptake in high-speed solid-state devices is demonstrated using an ion gel electrolyte. This is compared to a polymerized ionic liquid (PIL) electrolyte to understand how ion pair uptake affects device characteristics. Using X-ray photoelectron spectroscopy, the passive uptake of ion pairs from the ion gel into the OMIEC is detected, whereas no uptake is observed with a PIL electrolyte. This is corroborated by X-ray scattering, which reveals morphological changes to the OMIEC from the uptake of ion pairs. With in situ Raman, a reorganization of both anions and cations is then observed during gating. Finally, the speed and retention of OMIEC-based neuromorphic devices are tuned by controlling the freedom of charge motion in the electrolyte.
  • The ultralow thermal conductivity and tunable thermoelectric properties of surfactant-free SnSe nanocrystals

    Mir, Wasim Jeelani; Sharma, Anirudh; Villalva, Diego Rosas; Liu, Jiakai; Haque, Mohammed; Shikin, Semen; Baran, Derya (RSC Advances, Royal Society of Chemistry (RSC), 2021-08-19) [Article]
    Most studies to date on SnSe thermal transport are focused on single crystals and polycrystalline pellets that are obtained using high-temperature processing conditions and sophisticated instruments. The effects of using sub-10 nm-size SnSe nanocrystals on the thermal transport and thermoelectric properties have not been studied to the best of our knowledge. Here, we report the synthesis of sub-10 nm colloidal surfactant-free SnSe NCs at a relatively low temperature (80 °C) and investigate their thermoelectric properties. Pristine SnSe NCs exhibit p-type transport but have a modest power factor of 12.5 μW m−1 K−2 and ultralow thermal conductivity of 0.1 W m−1 K−1 at 473 K. Interestingly, the one-step post-synthesis treatment of NC film with methylammonium iodide can switch the p-type transport of the pristine film to n-type. The power factor improved significantly to 20.3 μW m−1 K−2, and the n-type NCs show record ultralow thermal conductivity of 0.14 W m−1 K−1 at 473 K. These surfactant-free SnSe NCs were then used to fabricate flexible devices that show superior performance to rigid devices. After 20 bending cycles, the flexible device shows a 34% loss in the power factor at room temperature (295 K). Overall, this work demonstrates p- and n-type transport in SnSe NCs via the use of simple one-step post-synthesis treatment, while retaining ultralow thermal conductivity.
  • Manipulating crystallization dynamics through chelating molecules for bright perovskite emitters

    Zou, Yatao; Teng, Pengpeng; Xu, Weidong; Zheng, Guanhaojie; Lin, Weihua; Yin, Jun; Kobera, Libor; Abbrent, Sabina; Li, Xiangchun; Steele, Julian A.; Solano, Eduardo; Roeffaers, Maarten B. J.; Li, Jun; Cai, Lei; Kuang, Chaoyang; Scheblykin, Ivan G.; Brus, Jiri; Zheng, Kaibo; Yang, Ying; Mohammed, Omar F.; Bakr, Osman; Pullerits, Tönu; Bai, Sai; Sun, Baoquan; Gao, Feng (Nature Communications, Springer Science and Business Media LLC, 2021-08-10) [Article]
    AbstractMolecular additives are widely utilized to minimize non-radiative recombination in metal halide perovskite emitters due to their passivation effects from chemical bonds with ionic defects. However, a general and puzzling observation that can hardly be rationalized by passivation alone is that most of the molecular additives enabling high-efficiency perovskite light-emitting diodes (PeLEDs) are chelating (multidentate) molecules, while their respective monodentate counterparts receive limited attention. Here, we reveal the largely ignored yet critical role of the chelate effect on governing crystallization dynamics of perovskite emitters and mitigating trap-mediated non-radiative losses. Specifically, we discover that the chelate effect enhances lead-additive coordination affinity, enabling the formation of thermodynamically stable intermediate phases and inhibiting halide coordination-driven perovskite nucleation. The retarded perovskite nucleation and crystal growth are key to high crystal quality and thus efficient electroluminescence. Our work elucidates the full effects of molecular additives on PeLEDs by uncovering the chelate effect as an important feature within perovskite crystallization. As such, we open new prospects for the rationalized screening of highly effective molecular additives.
  • All Set for Efficient and Reliable Perovskite/Silicon Tandem Photovoltaic Modules?

    de Bastiani, Michele; Babics, Maxime; Aydin, Erkan; Subbiah, Anand Selvin; Xu, Lujia; De Wolf, Stefaan (Solar RRL, Wiley, 2021-08-10) [Article]
    Over the last few years, perovskite solar cells have arisen as a technology to potentially side with mainstream silicon photovoltaics to help drive the transition towards renewable sources of energy. The coupling of perovskites with silicon in a tandem configuration may accelerate this development owing to the remarkably high power-conversion efficiencies possible with such devices. However, most of the perovskite/silicon tandem achievements so far have been confined to the lab environment, with only a few reported tests under outdoor conditions, using packaged devices. Nevertheless, one of the major challenges for perovskite/silicon tandem technologies, besides scale-up, lies in the cell-to-module (CTM) translation, which for the perovskite/silicon tandem concept is complicated by perovskite-imposed constrains such as a low temperature resilience, imposing challenges regarding tabbing and lamination, as well as a high sensitivity to moisture ingress, mandating the search for adequate encapsulation materials and methods. In this article, we describe and assess these challenges in depth and give a perspective on future directions towards module design, tailored for perovskite/silicon tandem photovoltaics, combining high performance with excellent durability. Our discussion also holds relevance for all-perovskite and other emerging photovoltaic technologies seeking market entry.
  • Modeling of n -Alkanes on Calcite/Dolomite by Molecular Dynamics Simulations and First-Principles Calculations

    Li, Huifang; Vovusha, Hakkim; Sharma, Sitansh; Singh, Nirpendra; Schwingenschlögl, Udo (Advanced Theory and Simulations, Wiley, 2021-08-08) [Article]
    Using a combination of molecular dynamics simulations and first-principles calculations, the interaction of n-alkanes with {101⎯⎯4} calcite/dolomite is investigated. It is observed that the n-alkane molecules align preferentially parallel to the interface, despite interaction by weak physisorption, and give rise to distinct adsorption layers. The ordering turns out to be more pronounced on calcite than dolomite due to a smaller average velocity of the n-alkane molecules. The observations are explained in terms of adsorption energies and charge transfers. The results show that functionalization is no prerequisite of structural ordering and a distinct mass density profile perpendicular to the interface.
  • Determining Out-of-Plane Hole Mobility in CuSCN via the Time-of-Flight Technique To Elucidate Its Function in Perovskite Solar Cells

    Mohan, Lokeshwari; Ratnasingham, Sinclair R.; Panidi, Julianna; Daboczi, Matyas; Kim, Ji Seon; Anthopoulos, Thomas D.; Briscoe, Joe; McLachlan, Martyn A.; Kreouzis, Theo (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-08-07) [Article]
    Copper(I) thiocyanate (CuSCN) is a stable, low-cost, solution-processable p-type inorganic semiconductor used in numerous optoelectronic applications. Here, for the first time, we employ the time-of-flight (ToF) technique to measure the out-of-plane hole mobility of CuSCN films, enabled by the deposition of 4 μm-thick films using aerosol-assisted chemical vapor deposition (AACVD). A hole mobility of ∼10–3 cm2/V s was measured with a weak electric field dependence of 0.005 cm/V1/2. Additionally, by measuring several 1.5 μm CuSCN films, we show that the mobility is independent of thickness. To further validate the suitability of our AACVD-prepared 1.5 μm-thick CuSCN film in device applications, we demonstrate its incorporation as a hole transport layer (HTL) in methylammonium lead iodide (MAPbI3) perovskite solar cells (PSCs). Our AACVD films result in devices with measured power conversion efficiencies of 10.4%, which compares favorably with devices prepared using spin-coated CuSCN HTLs (12.6%), despite the AACVD HTLs being an order of magnitude thicker than their spin-coated analogues. Improved reproducibility and decreased hysteresis were observed, owing to a combination of excellent film quality, high charge-carrier mobility, and favorable interface energetics. In addition to providing a fundamental insight into charge-carrier mobility in CuSCN, our work highlights the AACVD methodology as a scalable, versatile tool suitable for film deposition for use in optoelectronic devices.

View more