Photochemical Conversion and Storage of Solar Energy - ACS Energy

3 days ago - Key Laboratory of Photovoltaic and Energy Conservation Materials, Institute of Applied Technology, Hefei Institutes of Physical Science, ...
0 downloads 0 Views 5MB Size
Download PDF
http://pubs.acs.org/journal/aelccp

Photochemical Conversion and Storage of Solar Energy The first plenary lecture given by Michael Grätzel (É cole Polytechnique Fédérale de Lausanne (EPFL), Switzerland) provided an overview of the history of semiconductor photoelectrochemistry since the 1970s when artificial photosynthesis was in its infancy. Later in 1991, following the progressive development of nanotechnology and synthetic dyes with broad spectral response, strategical coupling of mesoscopic TiO2 films with Ru dyes led to his great invention of the dyesensitized solar cell (DSC), and the engineering installation of colorful semitransparent DSC panels in the SwissTech Convention Center on the EPFL campus was shown. Then the recent advances in PSC materials and devices were addressed in detail. The design concept was extended to the field of solar fuel synthesis, and high-efficiency photoelectrochemical cells for H2 generation and CO2 reduction were highlighted. The power conversion efficiency (PCE) of PSC increased sharply from 3.8% in 2009 to 23.3% in 2018, which is now comparable to that of crystalline silicon solar cells, while stability remains an issue. From another angle, the presentation by Prashant V. Kamat ranged from semiconductor quantum dot (QD) solar cells to hybrid and all-inorganic (CsPbBr3) PSCs. The light-induced charge carrier generation and transport across interfaces and the influences of the qualities of films and interfaces on cell stability were discussed. In addition, perovskite light-emitting diodes (LEDs) with strong and narrow emission were addressed for promising industrial applications. Hybrid Organic−Inorganic Perovskite Solar Cells. In this highlighted session of IPS-22, the golden triangle, namely, efficiency, cost, and stability, of hybrid pervoskite solar cells was comprehensively discussed. Efficiency was the hottest subject, and a world record of 23.3% has been reached. The cell efficiency value can be independently certified by different bodies. However, the definition of stability has not been standardized. Various different measurement conditions have been reported. Ultimately, survival of the device at a high temperature in sunlight is the only relevant condition, and Michael Grätzel set that hurdle as 1000 h at 60 °C, the practical temperature of a solar cell in use. Sang-Il Seok shared his experiences in high-efficiency PSC fabrication. During the past years, he has set several world record performances. Both Nam-Gyu Park and Liyuan Han presented their fabrication techniques for large-area perovskite films and modules with low defect density. A large-area, stable, and hysteresis-free PSC has been produced by Park through the combination of a Lewis acid−base adduct, interfacial engineering, and coating techniques. Han reported the development of a new graded heterojunction structure of PSCs using formami-

ACS Energy Lett. Downloaded from pubs.acs.org by 46.161.59.39 on 01/09/19. For personal use only.

T

he 22nd International Conference on Photochemical Conversion and Storage of Solar Energy (IPS-22) was held in Hefei, China, July 29−August 2, 2018. “Every two years, after the Olympic Games or after the FIFA World Cup, IPS is held,” said Detlef W. Bahnemann (Leibniz University of Hannover, Germany), Chairman of the 20th and 21st IPS. This humorous statement about the meeting time also demonstrates that the 44 year long tradition of the IPS conference series has been once again continued. According to the recall of Prashant V. Kamat (University of Notre Dame, U.S.A.), IPS-0 was initiated as a workshop on “The Current State of Knowledge of Photochemical Formation of a Fuel” in 1974 and chaired by Norman N. Lichtin (Boston University, U.S.A.).1,2 To date, the IPS series has been one of the most important conferences in the fields of photochemistry and solar energy utilization, offering a brilliant platform to discuss the latest advances in renewable energy research and to enhance regional and international collaborations. The IPS torch was passed to China again 26 years later after the ninth IPS conference in Beijing,2 1992, chaired by Songyuan Dai (North China Electric Power University, China) and Jinhua Ye (Tianjin University, China and National Institute for Materials Science (NIMS), Japan). Figure 1 is a group photo of the representatives of local organizers and international organizing committee at the conference opening ceremony. IPS22 attracted over 800 delegates, 14 plenary talks, 35 keynote talks, 105 invited and oral presentations, and 233 poster presentations. A broad range of topics was covered and organized into the following sessions: 1. Solar water splitting and CO2 conversion 2. Environmental and synthetic photocatalysis 3. Photoelectrochemical conversion and devices 4. Molecular and biomimetic photosynthesis 5. Photoinduced charge carrier transfer, mechanism, and modeling 6. Hybrid organic−inorganic perovskite solar cells 7. Dye-sensitized solar cells/organic solar cells 8. Semiconductor quantum dots and perovskite materials for luminescence 9. Novel photovoltaic materials and devices 10. Energy storage materials, devices, and applications Sessions 1−5 focused on photo(electro)catalysis, while topics 6−9 were mainly about photoelectrochemical devices, typically novel thin-film solar cells. Regarding session 10, it is the first time that IPS listed it as an individual topic, in view of particular importance of solar energy storage. Perovskite solar cells (PSCs, session 6) were the dominant topic of IPS-22 due to their rapid rise as a promising future photovoltaic technology. Besides, research on semiconductor photocatalysis for solar fuel synthesis and environmental applications (sessions 1 and 2) retained strong interest. Figure 2 gives a snapshot of a plenary talk at IPS22. © XXXX American Chemical Society

Received: December 11, 2018 Accepted: December 24, 2018

405

DOI: 10.1021/acsenergylett.8b02411 ACS Energy Lett. 2019, 4, 405−410

Energy Focus

Cite This: ACS Energy Lett. 2019, 4, 405−410

Energy Focus

ACS Energy Letters

Figure 1. Local organizer and international organizing committee members at the conference opening ceremony, IPS-22 meeting in Hefei, China. (Photo courtesy of Xin Xia.)

Figure 2. Prof. Michael Grätzel delivering the Plenary Lecture at the IPS-22 meeting, Hefei, China. (Photo courtesy of Xin Xia.)

based multication perovskite cells yield PCEs over 21% and Voc values above 1.15 V and in ambient air exhibit thermal stability in a wide temperature range (−80 to 100 °C). Such performance enables perovskite devices to work as a power source of highoutput voltage even under weak light. Joseph Luther produced cubic-phase CsPbI3 QDs with a high open-circuit voltage of >1.2 V and PCE over 13%, which has potential application in both photovoltaics and LEDs. As well as competing on the PCE and thermal stability, removing the lead is another important issue that may affect the acceptance of PSCs. Shuzi Hayase proposed halogenated SnPb and SnGe PSCs to reduce the use of Pb. The lead-free SnGe mixed metal PSC shows good stability in ambient atmosphere and yields a PCE of 7.9%, while the SnPb PSC offers an energy efficiency of 18.9%. Eric Wei-Guang Diau and his group investigated the role of ethylenediammonium diiodide (EDI2) additives in FASnI3 perovskite. They concluded that the presence of EDI2 can serve to control the film morphology,

dinum perovskite (PCE of 19.2%) and fabricated large-area perovskite films via a soft-cover deposition method. The research of Yi-Bing Chen has been focused on chemical modification and charge recombination of the interface between the perovskite layer and the hole transport material (HTM) layer. It was suggested that the band alignment at the perovskite−HTM interface can be tuned to improve the solar cell efficiency via adsorption of para-substituted benzenethiol molecules on the surface of the perovskite layer. A PCE of 20.2% can be achieved through this method, and more importantly, benzenethiol modification resulted in a significant improvement in stability of PSCs. A state of art PSC with a certified PCE of 22.7% was achieved through manipulation of the defects at grain boundaries and engineering of the interconnecting heterojunction, as presented by Yang Yang. In consideration of thermal stability and output voltage, Tsutomu (Tom) Miyasaka proposed that metal oxide electron transport layers (ETLs) could significantly benefit the thermal stability and elevate the output voltage of the PSC. TiO2 ETL406

DOI: 10.1021/acsenergylett.8b02411 ACS Energy Lett. 2019, 4, 405−410

Energy Focus

ACS Energy Letters minimize the Sn2+/Sn4+ oxidation, and reduce the defect states at the surface for better charge separation. Several speakers discussed the degradation of PSC devices in more detail under the extrinsic conditions of high temperature, strong light, oxygen, and moisture and the intrinsic conditions of phase changes, surface chemistry, grain boundaries, twinning, and composition variation. A variable in the design of the cells was the range of structures, p−i−n planar, p−i−n mesoporous, and n−i−p inverted. From an intrinsic viewpoint, the mesoporous designs were seen as less stable due to the higher surface area susceptible to recombination and chemical degradation, while there were a range of inert capping concepts and materials suggested to protect the PSC such as perylene. However, it was recognized that the classical MAPbI3 and FAPbI3 formulations may be inherently unstable as a result of the breakdown of the molecules when subject to attack by moisture, a likely event over long-term exposure to the atmosphere. This breakdown explained why additional PbI2 can enhance or partially stabilize efficiency as the formation of this compound is the first step in humidity-based degradation. The second degradation step of formation of HI from the MAI leads to creation of iodine that is mobile in the structure. Hence, there were some presenters who effectively proposed that every component of the most well-known formulation, MAPbI3, is unstable. This was the reasoning behind the significant number of papers dealing with solid-state devices. Here the Goldschmidt tolerance factor was the subject of discussion along with recognition that the cubic phase of the perovskite is the preferred phase for high stability. Meanwhile, Wanjian Yin proposed an additional criterion, the octahedral factor, the relationship between the radii of the B and X ions. Songyuan Dai systematically studied the mechanism of the instability of the APbI3 compounds and designed and prepared new mixeddimensional [(NH4)2.4(FA)n−1PbnI3n+1.4]0.85(MAPbBr3)0.15 hybrid perovskites and used these as an absorber in solar cells. Notably, when the unsealed mixed-dimensional perovskite device was stored under humidity over 90% for 24 days, the PCE showed no apparent decrease, demonstrating an excellent long-term stability under this test condition. With the long-term stability and high-efficiency properties, the mixed-dimensional perovskites might replace the traditional perovskite materials and show good commercialization prospects. Returning to performance enhancement, those who had a previous history in DSC could recognize some well-known chemical techniques to improve both efficiency and stability such as tBP and guanadimium. Those who based their designs on the tolerance factor had found that addition of K+ to the A site helped to stabilize and enhance the performance. A number of other cation modifications were reported, particularly by those who had based the perovskite on tin as an alternative to the more toxic lead, in which case one of the challenges to be addressed is to stop the oxidation of the divalent tin. From the wide selection of component ions presented, there are still many openings for perovskite compositions, including modifying the X component by partially or fully removing the iodide, with bromide being currently the preferred alternative, while performance suffers. Of course, the PSC is not simply the perovskite layer, and each other element, electron conductor, ETL, hole transport layer (HTL), and hole conductor (HTM) attracted the attention of speakers. Enhancement of the interface connection to the ETL involved a distinctly broad range of additives, coatings, and dopants, with no particular winner in this race yet, though the argument for polystyrene was persuasive. The HTM has

attracted a lot of attention, with the recognition that the classical spiro from the organic photovoltaic (OPV) era is both too expensive and unstable. Both organic and inorganic hole conductors were demonstrated, some going back to the early days of solid-state DSCs at EPFL, with the likely winners coming from inorganic candidates such as CuSCN and LiCoO2 and high-stability organics such as the phthalocyanines, maybe compounded with nickel. However, the door is still wide open for new candidates. These alternatives also eliminate the need to protect the Au conductor from metal ion migration through the HTM. However, more appropriate treatment may be to eliminate gold as the conductor and replace it with a cheap and stable alternative such as either Cu or carbon, even though the initial “hero” efficiency may suffer. The promoters of high stability for outdoor long life contend that stable PSCs at 20% will compete effectively in the electricity market. At this conference, there was not much attention on low light advantages of PSCs that make it such a good candidate for BIPV and any city condition for which the conference major sponsor SunGrow is developing systems. Several talks addressed manufacturing, including the recognition that spin coating with only about 1% material utilization and non/continuous deposition must be replaced by blade or slot die printing and that the coating solutions must be resistant to atmospheric conditions. One approach is to utilize solvents such as acetonitrile that have a high vapor pressure to displace water. Antisolvents also attracted attention as did soft-cover technology in both cases to produce smooth perovskite films of controlled thickness. However, it seems that the current technology status depends on capping of the perovskite with a hydrophobic organic material or with a thin layer of an inorganic such as lead sulfate. In statistical summary, the number of papers currently published on PSCs is more than 9000 and still growing rapidly. It seems that AI will become a necessary tool to analyze the relationships between the vast array of materials, designs, and processes. Photocatalysis, Photoelectrochemical Conversion, and Devices were extensively discussed in sessions 1−5. Six plenary presentations were delivered by Michael R. Hoffman, Detlef W. Bahnemann, Wonyong Choi, Licheng Sun, James R. Durrant, and Bunsho Ohtani, respectively. Michael R. Hoffman’s lecture emphasized the use of atomic layer deposition (ALD) in precisely tuning the surface charge densities of electrocatalysts for efficient oxygen and chlorine evolution reactions (OER and CER). Bahnemann addressed the urgent challenges in photocatalytic organic synthesis. The key issue lies in how to control the interfacial charge transfer process so as to achieve a high selectivity and yield. Especially, a nonselective photo-oxidation process by a hole and derivatives should be well controlled. Choi presented strategies for designing coupled semiconductors with heterojunctions at the interface for efficient photo(electro)catalytic solar fuel synthesis and environmental remediation, with special emphasis on the photoreductive O2 activation for H2O2 production. Sun summarized their research progress in artificial photosynthesis during the past 20 years in Sweden with his colleagues. A range of dye molecules were synthesized for various photochemical conversion systems. Durrant provided illumination on photocatalysis kinetics based on LEDs, rather than lasers. Transient absorption spectroscopy (TAS) has been employed to measure the photogenerated hole lifetime and investigate the kinetic dependences of photocatalysis in TiO2 films of varying 407

DOI: 10.1021/acsenergylett.8b02411 ACS Energy Lett. 2019, 4, 405−410

Energy Focus

ACS Energy Letters morphology. Ohtani developed reversed double-beam photoacoustic spectroscopy as a powerful characterization tool for charge carriers (using TiO2 photocatalysis as the baseline). He captivated the audience through a personal image analogy with Steve Jobs, how the current criteria for defining a photocatalyst is inadequate, concluding that active photocatalysts are all alike but every inactive one is inactive in its own way. At IPS-22, several presentations concentrated on the active photocatalysts and related strategies to photocatalytic activity enhancement. TiO2 and its coupled systems were still the most popular photocatalysts. Fundamental studies mainly focused on crystal and band engineering, surface modification, charge carrier transfer, and the underlying photocatalytic reaction mechanism. Their applications in photocatalytic solar fuel production, CO2 reduction, and environmental purification were comprehensively discussed, and novel characterization techniques have been developed to improve the deep understanding of the relationship between surface properties and the photocatalytic mechanism of nanosized TiO2. Polymeric g-C3N4 was another hot photocatalyst owing to its metal-free nature, nontoxicity, processability, and stability. Photocatalytic Cr(VI) reduction, organic degradation, CO2 reduction, H2 generation, and bacterial inactivation were addressed by several scientists. Bi-containing (e.g., BiVO4, Bi2O3, Bi2Sn2O7, BiOBr, and BiOCl) photocatalysts attracted attention. It may be easy to see that using single-component photocatalysts is insufficient to achieve high photocatalytic activity. Several novel coupling systems have been developed to suppress the large quantity of charge carrier recombination widely occurring in single semiconductor systems. Various narrow-band semiconductors, plasmonic metal nanoclusters, surface grafting, Ru-complex sensitizers, cobalt sulfide, and phosphosulfide were developed to extend the light absorption spectrum and to improve the charge carrier separation. Typically, when two different band structure semiconductors are coupled, a heterojunction, p−n homojunction, and Zscheme photocatalyst can be built up. The last mentioned presents a new class of photocatalyst in which charge carriers separate through recombination between electrons in the lower conduction band and holes in the higher valence band, and these were heatedly discussed by Akihiko Kudo, Jiaguo Yu, Hiroshi Irie, Ji-Jun Zou, Xiwang Zhang, Qiuye Li, and Zaicheng Sun. However, the methodology of the underlying interfacial charge carrier transfer was still ambiguous. Moreover, 2D nanomaterials, such as the graphene family and MoS2, were used as electron collectors for coupled photocatalysts, efficient water splitting, CO2 reduction, and environmental disinfection by Xiwang Zhang, Jungang Hou, and Xuanhua Li. Potential applications of TiO2 photocatalysis discussed were largely in the environmental area, which included:

• two very interesting applications in the biological field, production of rare sugars and improvement of germination of seeds, both using photocatalysis by Kazuya Nakata. Nanostructured photoelectrochemical electrodes were also fabricated for solar water splitting. Photocathodes of Cu2Omodified or -coupled TiO2 and α-Fe2O3 photoanodes, Cu3Nb2O8, nanostructured p-type Si, and photoanodes of SrTaO2N, LaTaO2N, β-Fe2O3, YFeO3, and Ta3N4 were presented. Tandem cells based on Si, PSC, and DSC for solar water splitting were developed to improve the solar to hydrogen conversion efficiency. A heated discussion about the photoinduced charge carrier transfer mechanism occurred. DSCs and OPVs. DSC, a low-cost solar cell belonging to the group of thin-film solar cells, has been widely considered as a suitable option for low-density applications. Malapaka Chandrasekharam from CSIR-Indian Institute of Chemical Technology (IICT) spoke about synthesis and evaluation of stable and efficient new metal-free organics, phthalocyanine as well as ruthenium-based dyes, as sensitizers for DSC application. Their work achieved a certified world record efficiency of 11.40% employing a small organic molecule, designed and developed at IICT, as the coadsorbent in a black dye-based device. Kyungkon Kim demonstrated colorful, semitransparent OPVs with a single broad-band-absorbing active material of fixed thickness using Ag−TiOx−Ag color filters (CFs). The CF enables the OPV to transmit spectrally pure colors with peak transmission efficiencies surpassing 25% and allows the colors to be freely tuned without disturbing the charge transport properties such that the device performance stays consistent. Wenping Hu introduced newly developed applications of 2D form nanostructures in optoelectronic devices. Zhen Li delivered a lecture about the structure-packing and functionality relationship of π-molecules with different optoelectronic properties. Quantum Dots and Luminescence. Regarding semiconductor QDs for luminescence applications, all-inorganic perovskite cesium lead halide has been extensively discussed as a promising material for next-generation light-emitting diode QDs. This is due to the outstanding photoluminescence (PL) properties of this type of material and benefits from quantum effects. Jianjun Tian reported the synthesis of core−shell structured cubic CsPbBr3(α-CsPbBrx) perovskite QDs via a facile hot injection method and centrifugation process. The core−shell structure QDs showed a record blue emission PL quantum yield (PLQY) of 84%. By transformation of the crystal structure into a highly crystallized γ phase, the record blue PLQY can rise to 91% at 480 nm. However, the development of metal halide perovskite LEDs has been impeded by their fast carrier diffusion and poor stability in bias conditions. A 2D core−shell structure (i.e., quasi-2D CsPbBr 3 quantum well homogeneously surrounded by inorganic crystalline Cs4PbBr6 of large bandgap) was designed and synthesized by Zhijun Ning to facilitate radiative recombination with a high PLQY and improve the device operational lifetime. Longwei Yin reported the extra long term stable cubic CsPbI3 prepared by polymer polyvinylpyrrolidoneinduced surface passivation engineering. Such obtained cubicCsPbI3 PSCs exhibit an extra long carrier diffusion length, high PCE, and excellent thermal/moisture stability. Besides exploring the PL properties of novel metal halide perovskites, several presentations were focused on how to achieve unconventional properties and high performance by engineering conventional PL materials, e.g., CdSe and CdS, at

• metal inks photodeposited on the surface of various commercial TiO2 films for metal micropatterns and photocatalytic activity assessments by Andrew Mills • self-cleaning and plasmon-free surface-enhanced Raman scattering (SERS) and substrate fabrication by grafting chiral carbon nanotubes with TiO2 nanocrystals by Jinlong Zhang • conversion of ethylbenzene to (R)-1-phenylethanol with highly selective activation of C−H bonds by strategic cooperation of photocatalytic-generated H2O2 with enzymes by Jonathan Z. Bloh 408

DOI: 10.1021/acsenergylett.8b02411 ACS Energy Lett. 2019, 4, 405−410

Energy Focus

ACS Energy Letters

• Guozhong Cao compared the electrochemical properties of Mn-based (MnO, MnS, and MnNCN) electrodes for Li-ion capacitors. MnO mesocrystals as promising anodes offer a high capacity of 637 mAh/g at 100 mA/g and excellent cycling performance against degradation. For MnNCN, the more covalent bonding nature of Mn−N leads to a lower discharge potential in Li-ion batteries. Metastable MnS was demonstrated to be a better choice for Li-ion battery anodes than the stable MnS. • Shihe Yang presented preparation strategies in interfacing and assembling various nanostructures by solution processes. The resulting architectures have been explored as electrocatalysts and photoelectrochemical electrodes. • Guoxiu Wang presented their progress in materials nanoarchitecture design of graphene nanosheets, tingraphene and silicon-graphene nanocomposites for highrate or high-capacity lithium/sodium/potassium batteries. • Jana Timm shared their cell and stack design for their newly developed photoelectrocatalytic redox flow batteries by strategically integrating the technologies of TiO2 photoelectrocatalysis and vanadium redox batteries. • Yanglong Hou delivered a talk to introduce the rational design of carbon nanoarchitectures as cathodes for lithium−sulfur batteries. A high sulfur loading up to 90% was achieved for novel hollow graphene nanoshells, with very stable cycling life. • Haobin Wu discussed the application of nanostructured materials derived from metal−organic frameworks (MOFs) as electrode materials for batteries and electrocatalysts for generation of fuels, as well as composite electrolytes developed with the assistance of MOFs. • Weiqing Yang utilized two novel materials of hierarchical tubular carbon nanotubes and 2D Ti3C2Tx as electrodes of a flexible microsupercapacitor. • Ying Wang showed a porous heterostructured MoO2/ Mo2N nanobelt cathode for rechargeable zinc-ion batteries. Prospects and Conclusions. A prosperous picture of solar energy utilization and its related research was shown at IPS-22. It is no doubt that PSCs caught the spotlight. Meanwhile, more conventional topics such as photocatalysis and photochemical conversion are still bursting with vitality and reserving new potentials. A few topics may become marginally important compared with their popularity in the previous years. However, good science does not concern popularity; the emerging hot topics are rather new sprouts developed from old roots. The organizer of each IPS conference has to have a balance between the hot spots and fundamental questions of solar energy conversion. At IPS-22, a very condensed and well-organized schedule was carefully planned by the local conference organizer. A number of awards, including young talents and poster awards, were granted to recognize research students and young scholars for their participation and excellence. The local government of Anhui Providence and Hefei City offered tremendous support for this international event. In a sense, this reflects the recognition by the Chinese government of the essential role of solar cell technology and photochemistry for a green energy future. Promoting renewable energy and a green economy has become the main objective of China’s science and technology policy in recent years. The nation made great efforts to shift away from energy

the nanoscale probe/film interface, another important issue raising general interest. Chaodan Pu and Xiaogang Peng from Zhejiang University had identified common electron and hole traps on typical QDs and reported the synthesis approach of monodisperse colloidal CdSe/CdS core−shell QDs with nearly 100% radiative decay in the intrinsic PL decay channel. Jinxing Zhang proposed a novel nanoscale bandgap engineering approach via visible light excitation across the inhomogeneous BiFeO3 ferroelectric interface. The high photoelectric performance in this complex oxide indicates that the induced photovoltaic, photoemission, and photocatalyst effects applied in the visible light region may be integrated with future microelectronic devices. Novel Photovoltaic Materials. To supplement sessions 6−8, some other novel photovoltaic materials and devices have been discussed under this theme, among which, colloidal quantum dot (CQD) solar cell devices based on PbS are a compelling idea owing to their tunable bandgap, broad light adsorption spectrum, solution processablility, low loss, and high stability (though toxic). Chengwu Shi deposited novel compact PbS QD thin films on TiO2 nanorod arrays and demonstrated a considerably high conversion efficiency. Wanli Ma developed CQD solar cells using both PbS and emerging CsPbI3 perovskite QDs with PCEs up to 12.55%. Haibin Wang combined PbS QD and ZnO nanowire structures to promote carrier transport and light absorption in the near-infrared region. By employing a PbS sensitized solar cell and TeO2 capping layer, Xiaoliang Zhang composed stable semitransparent QD solar cells with a PCE of 8.4%. As well as PbS, Sb2Se3, ZCISe, and CZTSSe also attracted great attention for their promising photovoltaic properties and QD applications. Jiang Tang reviewed their recent progress in Sb2Se3 thin-film photovoltaics, including the basic chemical and optoelectronic properties of Sb2Se3; 7.6% CdS/Sb2Se3 solar cells with a Sb2Se3 layer were produced by vapor transfer deposition, and a 5.9% ZnO/Sb2Se3 device was demonstrated to present outstanding stability. Xinhua Zhong developed a capping ligandinduced self-assembly approach for the deposition of Zn−Cu− In−Se (ZCISe) alloy QDs on a TiO2 electrode, offering a certified PCE of 11.6%. Yi Zhang investigated the interface of Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells. Dai-Bin Kuang proposed a lead-free Cs2AgBiBr6 double perovskite nanocrystal structure that exhibited excellent stability and performed photocatalytic CO2 reduction. In addition, a novel cone-shaped Si nanohole (SiNH) structure has been designed and fabricated to enhance the interface contact between SiNHs and an organic layer using an advanced metal-assisted chemical etching method, as presented by Shanglong Peng. There are abundant material options still to explore for QD solar cells. Energy Storage Materials and Batteries. It was the first time for IPS series to launch an individual session for energy storage technology, considering “energy storage could be the most critical part of the future of photovoltaics” (as John Bell mentioned in his talk). A wide range of electrochemical devices for energy storage including Li-ion batteries, Li−S batteries, redox flow batteries, supercapacitors, and solar fuels were covered and discussed in this session. • Hong Li summarized current developments in energy storage technology at the Institute of Physics, Chinese Academy of Sciences. A long-term effort has been devoted to the commercialization of their solid-state lithium ion battery. 409

DOI: 10.1021/acsenergylett.8b02411 ACS Energy Lett. 2019, 4, 405−410

Energy Focus

ACS Energy Letters

Laboratory of Novel Thin Film Solar Cells, and Beijing Key Laboratory of Energy Safety and Clean Utilization.

generated from fossil fuels. The PV industry is one of the key fields that is still striving to upgrade the technology. In this context, IPS-22 provided a great opportunity to promote regional research cooperation and foster new collaborations and partnerships between academia and industry for solar energy utilization. We are grateful to all of the wonderful speakers and generous sponsors. Owing to their support, IPS-22 can be regarded as a big success in all aspects. IPS-23 will be chaired by Mohammad Khaja Nazeeruddin and held at EPFL, Switzerland. We are looking forward to a most successful IPS-23.

■

REFERENCES

(1) Bolton, J. R. The Photochemical Conversion and Storage of Solar Energy: An Historical Perspective. Sol. Energy Mater. Sol. Cells 1995, 38, 543−554. (2) Kamat, P. V. A Scientific Journey − Autobiographical Notes of Prashant V. Kamat. J. Phys. Chem. C 2018, 122, 13207−13209.

Xin Xia† Jia Hong Pan*,† Xu Pan‡ Linhua Hu‡ Jianxi Yao† Yong Ding† Defa Wang§ Jinhua Ye*,§,∥ Songyuan Dai*,† †

■

State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China ‡ Key Laboratory of Photovoltaic and Energy Conservation Materials, Institute of Applied Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China § TJU−NIMS International Collaboration Laboratory, Tianjin University, 92 Weijin Road, Tianjin 300072, China ∥ International Center of Materials Nanoarchitectonics (WPI−MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (J.H.P.). *E-mail: [email protected] (J.Y.). *E-mail: [email protected] (S.D.). ORCID

Xu Pan: 0000-0003-3770-7918 Linhua Hu: 0000-0002-0513-2999 Defa Wang: 0000-0001-7196-6898 Jinhua Ye: 0000-0002-8105-8903 Songyuan Dai: 0000-0001-5710-9208 Notes

Views expressed in this Energy Focus are those of the authors and not necessarily the views of the ACS. The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS

The authors gratefully acknowledge support of the National Basic Research Program of China (2016YFA0202400, 2014CB239300), the K.C. Wong Education Foundation, Hong Kong, and the National “111” Project (No. B16016). This work is supported by the National Natural Science Foundation of China (No. 51572080, 51772094, U1705256, 51702096, 51772095), Fundamental Research Funds for the Central Universities (No. JB2018ZD07, JB2016004), Beijing Natural Science Foundation (No. 2172052), Beijing Key 410

DOI: 10.1021/acsenergylett.8b02411 ACS Energy Lett. 2019, 4, 405−410