Table of Content

10 September 2023, Volume 44 Issue 9

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Preface

有机太阳能电池专刊

李永舫, 陈红征, 朱晓张, 何凤

2023, 44(9):  1-4. 

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Content

Cover and Content of Chemical Journal of Chinese Universities Vol.44 No.9(2023)

2023, 44(9):  1-6. 

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Review

Approaches to Achieving High-performance Semitransparent Organic Solar Cells

LI Yaokai, GUAN Shitao, ZUO Lijian, CHEN Hongzheng

2023, 44(9):  20230166.  doi:10.7503/cjcu20230166

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Semitransparent organic solar cells（STOSCs）， capable of generating electricity and transmitting light simultaneously， are a highly promising new energy technology with potential applications in building-integrated photovoltaics for windows and roofs， as well as in agricultural greenhouses and transportation vehicles. However， the balance between the power conversion efficiency（PCE） and average visible light transmittance（AVT） of STOSCs remains a challenge. Ideal high-performance STOSC requires a balance between increasing the AVT and PCE， which involves selectively absorbing and utilizing non-visible spectrum photons for energy conversion while transmitting visible spectrum photons to maintain aesthetic appeal and color purity. In this review， we discuss and summarize various approaches to achieving high-performance STOSC from the perspectives of active layer tuning strategy， device engineering and multifunctional STOSCs. Our findings provide valuable insights and recommendations to promote the research and development of this promising energy technology.



Research Progress of Semitransparent Organic Solar Cells

ZHENG Haolin, LIU Wuyue, ZHU Xiaozhang

2023, 44(9):  20230365.  doi:10.7503/cjcu20230365

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Semitransparent organic photovoltaics（ST-OPVs） have intrinsic advantages over other inorganic photovoltaics due to the tunable electronic energy levels and selective absorption spectra of the active layer material in applications such as power-generating roofs for greenhouses and color-adjustable windows for modern buildings and exterior walls. With the rapid development of highly efficient narrow bandgap polymer donors and near-infrared non-fullerene acceptor materials， ST-OPVs have made rapid advances in light utilization efficiency over the past decade.The intrinsic and optically modified semitransparent devices exceed 3% and 5%， respectively. In order to further promote the practical use of semitransparent organic photovoltaic， how to further improve the optical efficiency of the device is still the key research direction. Therefore， this paper reviews the recent important progress of ST-OPVs from the theoretical model of the semitransparent device， the design of the active layer material and the optical modification of the device， so as to provide a reference for the improvement of the device performance in the future.



Mechanical Parameters of Organic Photovoltaic Films： Manipulation and Prediction

SUN Bing, LI Saimeng, ZHOU Kangkang, PENG Zhongxiang, YE Long

2023, 44(9):  20230168.  doi:10.7503/cjcu20230168

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Organic photovoltaic cells（OPVs） have the advantage of being colorful， light weight and flexible， and have great application prospects in the field of transparent， wearable， and stretchable electronics. In this review， the manipulation strategies of mechanical properties are reviewed for high efficiency OPVs active layer films， and the prediction models of their mechanical properties are summarized. First， the mechanical properties of the OPV films and their testing methods are briefly introduced. Then， the manipulation methods and prediction models of the mechanical properties of OPV films， including polymer∶nonfullerene small molecule acceptor and all-polymer blends， are described with important examples. Finally， our insights into the future trend of this exciting direction are provided.



Research Progress of Electroactive Ionene-based Organic Photovoltaic Interlayers

SONG Yanan, YOU Zuhao, WANG Xu, LIU Yao

2023, 44(9):  20230167.  doi:10.7503/cjcu20230167

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Organic solar cells have attracted wide attention from academia and industry due to their advantages of light weight， flexibility， and printable preparation. The modulation and optimization of the soft/hard material interfaces between metal electrodes and organic semiconductor active layers is the research frontier of interface engineering in organic solar cells. The core of the research is the design and synthesis of new interlayer materials and their integration into devices. Ionene is an emerging class of non-conjugated polyelectrolytes-based interlayer materials， in which ionic species reside within the polymer backbone. Compared with traditional conjugated polyelectrolytes， the synthesis of ionene polymers is simple， the reaction conditions are mild and green， and it has higher ion concentration and stronger interfacial polarization capability， which is suitable for the interface modification of organic solar cells. Recent advances in electroactive ionene have stimulated the interest of researchers to explore the application of this novel polymer in organic electronic devices. In this review， the molecular design and synthesis of electroactive ionene polymers were reviewed， and the mechanism and function of these ionene polymers on interfacial modifications were discussed， as well as their charge transport property and the performance of interfacial energy level alignment.



Hierarchical Aggregates of Non-fullerene Electron Acceptors

LI Wei, CHEN Chen, LIU Dan, WANG Tao

2023, 44(9):  20230160.  doi:10.7503/cjcu20230160

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The photoactive layer of organic solar cells is composed of p-type electron donor and n-type electron acceptor. The conjugated structure and hetero-elements within these organic semiconducting molecules make them easy to self-assemble into aggregates， exhibiting distinct optoelectrical properties from those of individual molecules， and further determining the light absorption， exciton dissociation and charge transport processes in their solar cells. In this paper， the aggregation behaviors of n-type non-fullerene electron acceptors（NFAs） at molecular and micro- nano scales were presented， including the stacking， nucleation， crystallization mechanism of the strong-crystalline NFAs as well as their retarding approaches， and the random aggregation as well as ordering strategies for low-order NFAs. Finally， a summary and prospect of the structure design and aggregate control of NFAs were provided， with a special introduction of recent progresses on NFA fibrillization.



Progress on the Efficiency Regulation of Organic Solar Cells by Volatile Solid Additives

SONG Xin, GAO Shenzheng, XU Shanlei, XU Hao, ZHOU Xinjie, ZHU Mengbing, HAO Rulin, ZHU Weiguo

2023, 44(9):  20230151.  doi:10.7503/cjcu20230151

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Bulk heterojunction（BHJ） organic solar cells（OSCs） are considered a promising photovoltaic technology due to their solution-processability， eco-friendliness， non-toxicity， and flexibility. The nanoscale morphology of the active layer is a key factor that determines device performance and stability. Researchers have developed various morphology optimization methods， such as thermal annealing， solvent annealing， and solvent additives. However， these treatment methods are incompatible with large-area printing processes and may compromise the internal morphology and device performance stability. Consequently， it is essential to screen a simple yet efficient approach for morphology control in OSC area. In recent years， volatile solid additives have emerged as a feasible direction to improve the energy conversion efficiency（PCE） and stability of OSCs due to their unique molecular properties， which can form strong interaction forces with donor/acceptor molecules. This article systematically summarized the research status of non-halogenated and halogenated volatile solid additives in regulating the morphology and photovoltaic performance of OSCs. We deeply discussed the different mechanisms of optimizing active layer morphology by volatile solid additives， including molecular adsorption energy， interaction between donor and acceptor， crystal nucleation， and growth. Finally， this article analyzed the challenges and future development trends of volatile solid additive.



Recent Advances in the Application of Metal Complexes for Organic Solar Cells

WANG Jiarui, YU Runnan, TAN Zhan’ao

2023, 44(9):  20230150.  doi:10.7503/cjcu20230150

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Organic solar cells have attracted much attention due to their advantages of light weight， diverse colors， and potential for fabricating flexible large-area devices. The innovation of donor and acceptor materials and interface layers is key to improving the performance of organic solar cells. Metal complexes， which combine the self-assembly order of complex molecules with the structural diversity of organic molecules， have high triplet exciton density and long exciton lifetime， having been regarded as an important photoelectric functional material. With the in-depth study of the photoelectric properties， various metal complex photoelectric materials have been successfully applied in organic solar cells to achieve higher power conversion efficiency. In this paper， the applications of metal complexes based on platinum， zinc， iridium， ruthenium， zirconium， and other metals as active layer material， interface layers， and additives of organic photovoltaic devices are reviewed， and the structure-performance relationships are analyzed in depth. In the end， the perspectives on the challenges and opportunities for these materials are prospected to provide reference and inspiration for the design and application of high-performing metal complexes in organic photovoltaic devices.



Molecular Stacking and Device Performance： Recent Advances of Efficient Small Molecule Donors Based on Benzodithiophene and Its Derivatives

YANG Ke, XIAO Zeyun, LU Shirong, SUN Kuan

2023, 44(9):  20230123.  doi:10.7503/cjcu20230123

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The rapid development of all-small-molecule solar cell has recently gained recognition within the photovoltaic research community. Well-defined structure and less batch-to-batch variation empowered it great application prospects. In this perspective， we review the development of small molecule donors based on benzodithiophene（BDT） and its derivatives， with a focus on the relationship between molecule structure， stacking characteristics and device performance. By analyzing successful cases in the BDT series of small molecules， we aim to clarify the link between molecule structure， solid-state aggregation and device performance. We hope this discussion can be the minnow to catch the whale of highly efficient molecules in the future.



Article

Alkyl Chain Engineering of Bithiophene Imide-based Polymer Donor for Organic Solar Cells

BAI Yuanqing, ZHANG Jiabin, LIU Chunchen, HU Zhicheng, ZHANG Kai, HUANG Fei

2023, 44(9):  20230271.  doi:10.7503/cjcu20230271

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Two polymer donor materials， namely pBDT-BTI-EH and pBDT-BTI-ME， were synthesized by copolymerizing benzodithiophene（BDT） unit with bithiophene imide（BTI） unit containing 2-ethylhexyl and methyl alkyl side chains， respectively. Compared to pBDT-BTI-EH∶Y6 based organic solar cells（OSCs）， the pBDT-BTI-ME∶Y6-based device exhibited higher charge mobilities， reduced charge recombination， more efficient exciton dissociation， and favorable film morphology， which leaded to increased short current density（J_sc）， fill factor（FF） and thus a significant improvement in power conversion efficiency（PCE） from 9.31% to 15.69%.



Fused-benzotriazole Based p-Type Polymers： Fine-tuning on Absorption Band-width and Bandgap via Backbone Thiophene and Selenophene Strategies

TIAN Mei, ZHANG Zhiyang, ZHAN Chuanlang

2023, 44(9):  20230190.  doi:10.7503/cjcu20230190

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Four fused-benzotriazole based p-type polymers（BDT-TT， BDT-Se， BDD-TT， and BDD-Se） were designed and synthesized， and the fine-tuning on absorption band-widths and bandgaps via the backbone selenophene and thiophene strategies were reported. First， we introduced dithienothiophen［3，2-b］pyrrolobenzotriazole to co-polymerize with BDT-2F and synthesized BDT-TT. Then， we used selenophene to replace the thienothiophene units on the dithienothiophen［3，2-b］pyrrolobenzotriazole and synthesized BDT-Se. Compared to BDT-TT， BDT-Se showed a reduced bandgap from 2.0 eV to 1.89 eV. After that， we used BDD to replace BDT-2F and synthesized BDD-TT by co-polymerizing with dithienothiophen［3，2-b］pyrrolobenzotriazole. In comparison to BDT-TT， BDD-TT showed extended absorption band-width with the full-width-at-the-half-maximum（FWHM） increased from 138 nm to 229 nm and reduced bandgap from 2.0 eV to 1.71 eV. At last， we combined BDD and diselenophen［3，2-b］pyrrolobenzotriazole and synthesized BDD-Se， which achieved extended absorption and further reduced bandgap（1.61 eV）. Using PC₇₁BM as the electron acceptor material， the organic solar cells fabricated by the four polymers gave the efficiencies of 1%—2%.



Beta-alanine as a Dual Modification Additive in Organic Solar Cells

ZAFAR Saud uz, ZHANG Weichao, YANG Shuo, LI Shilin, ZHANG Yingyu, ZHANG Yuan, ZHANG Hong, ZHOU Huiqiong

2023, 44(9):  20230185.  doi:10.7503/cjcu20230185

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This work presents a novel approach to modify the interface of organic solar cells（OSCs） by using beta- alanine（β-alanine） which has a hydroxyl（—OH）/carboxyl group（—COOH） group on one side and amine（—NH₂） on the other side. As a dual modifier approach， β-alanine was applied to both the hole-transporting layer（HTL， PEDOT∶PSS） and electron-transporting layer（ETL）； PFN-Br was added in the same device through a simple solution-processed technique， resulting in the synthesis of new interface layers. β-alanine is soluble in polar aqueous solvents， and their soluble components in this work are methanol and water. Dual modification approach improved the power conversion efficiency（PCE） of PM6∶Y6 solar cells， increasing from 14.99% to 15.78% among with a single-sided approach. The hydrophobicity of both layers was enhanced as confirmed by contact angle and FTIR measurements， which blocked moisture and oxygen from interacting with their respective electrodes. The surface morphology was analyzed using AFM. The results showed that the amine group of β-alanine interacted with the —SO{}_{\mathrm{3}}^{-} group of PSS as well as with the bromine halogen（Br^‒） ion of PFN-Br， which reduced their concentration which elevated the hydrophobicity and improved the stability of the OSCs. Furthermore， the carrier mobilities for both the modified devices were improved， which was confirmed by the space-charge-limit current（SCLC） measurements.



Synthesis and Photovoltaic Properties of Non-fullerene Acceptors Based on Aryl-substituted Imide End Groups

SHI Shiling, JIANG Hanxi, TU Xueyang, XIAN Kaihu, HAN Dexia, LI Yanru, YAO Xiang, YE Long, FEI Zhuping

2023, 44(9):  20230182.  doi:10.7503/cjcu20230182

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The structure of end-group is of great significance for the photovoltaic properties of non-fullerene receptors（NFAs） in organic solar cells. We designed and synthesized three novel end groups with aryl-substituted imide structures（IIC-Ph， IIC-PhBr and IIC-Ph2F） and further prepared three NFAs with acceptor-donor（acceptor） donor-acceptor（A-DA'D-A） structure（BTP-IIC-Ph， BTP-IIC-PhBr and BTP-IIC-Ph2F）. The comparison of UV-Vis-NIR absorption spectra and theoretical simulation showed that IIC-PhBr and IIC-Ph2F had stronger electron-withdrawing ability than IIC-Ph， which enhanced the intramolecular charge transfer effect of NFAs and red-shift their absorption spectra. The introduction of electron-withdrawing Br and F atoms on the terminal benzene rings of acceptors lowered the frontier molecular orbital energy levels of BTP-IIC-PhBr and BTP-IIC-Ph2F. The power conversion efficiency（PCEs） of solar cell devices based on BTP-IIC-Ph， BTP-IIC-PhBr and BTP-IIC-Ph2F are 13.54%， 11.84%， and 11.58%， respectively. Comparison to BTP-IIC-PhBr and BTP-IIC-Ph2F， BTP-IIC-Ph based devices show higher PCE， which can be attributed to the higher open-circuit voltage（V_OC） due to its higher LUMO level， better exciton dissociation and less trap assisted carrier recombination.



Effect of Substitution Positions of Alkyl Chains in Small Molecular Donor Bridged Units on the Performance of Photovoltaic Devices

GUO Ziqi, JIAO Cancan, WU Simin, MENG Lingxian, SUN Yanna, KE Xin, WAN Xiangjian, CHEN Yongsheng

2023, 44(9):  20230180.  doi:10.7503/cjcu20230180

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Two isomeric small molecule donors， C2-C-F and C2-M-F， with only the different substitution positions of the alkyl chains on the intermediate bridged trithiophene units， were designed and synthesized. It was found that the alkyl chain substitution position has little effect on their absorptions and energy levels， but has a significant impact on the morphology of the active layers when blended with the acceptor BTP-4F-12. Better morphology was obtained for the active layer based on small molecule donor C2-C-F， and an efficiency of 12.84% was achieved for the C2-C-F-based photovoltaic device. This result indicates that the morphology of the active layer can be finely regulated through the alkyl substitution positions， providing a useful avenue for the design of efficient small molecule donors.



New Strategy to Balance the Miscibility and Phase Separation to Improve Organic Solar Cells Efficiency

ZHANG Lifu, WANG Xinkang, CHEN Yiwang

2023, 44(9):  20230177.  doi:10.7503/cjcu20230177

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Obtaining superior charge separation and charge extraction efficiency through tuning the gradient separation morphology of the active layer has been the goal of preparing high-performance organic solar cells（OSCs）. Here， we selected two non-fullerene acceptors， 3，9-bis｛2-methylene-［3-（1，1-dicyanomethylene）-indanone］｝-5，5，11，11-tetrakis（4-hexylphenyl）-dithieno［2，3-d∶2′，3′-d′］-sindaceno［1，2-b∶5，6-b′］-dithiophene（ITIC） and 3，9-bis （2-methylene-｛［3-（1，1-dicyanomethylene）-6，7-fluoro］-indanone｝）-5，5，11，11-tetrakis（4-hexylphenyl）-dithieno［2，3-d∶2'，3'-d'］-s-indaceno［1，2-b∶5，6-b'］dithiophene（IT-2F）， with different end groups as the third component. The conventional bulk-heterojunction（BHJ） and optimized pseudo-planar-heterojunction（PPHJ） ternary OSC devices were prepared by two active layer construction processes， named one-step deposition（O-SD） and distributed sequential deposition（T-SD）， respectively. It was found that the difference in the miscibility of the third component in the bulk-heterojunction films could regulate the phase separation morphology of the films. Among them， the phase separation increased significantly in the ternary films based on IT-2F and its device efficiency decreased to 9.25% compared to 12.02% of the binary device， while the phase separation morphology of the ternary films based on ITIC did not change significantly， the device efficiency increased slightly. It is worth noting that the active layer films with vertical distribution can be obtained by T-SD method， which avoids the effect of miscibility differences on the film morphology， the corresponding PPHJ device achieves an efficiency of over 13%. This work shows that the utilization of miscibility differences and sequential deposition processes to modulate the phase separation morphology of the active layer is an effective strategy for the preparation of high-performance organic solar cells.



Ternary Organic Photovoltaic Devices Based on Wide-band Gap Small Molecule Donor Third Component

MA Yifan, ZHANG Yamin, GAN Shengmin, ZHANG Yuchen, FEI Xian, WANG Ting, ZHANG Zeqi, GONG Xuezhu, ZHANG Haoli

2023, 44(9):  20230170.  doi:10.7503/cjcu20230170

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Ternary strategy is an efficient way for improving the performance of organic solar cell. In this work， a highly crystallized organic small molecular donor（DRDTBT） was designed and synthesized as the third component of ternary organic solar cells. The introduction of a large conjugated unit dithieno［3'，2'：3，4；2''，3''：5，6］benzo ［1，2-c］［1，2，5］thiadiazole with electron-withdrawing ability deepened the highest occupied molecular orbital level of DRDTBT as well as enhanced the crystallinity of it. When employed DRDTBT as the third component of PM6∶BTP-eC9 active layer， the open circuit voltage of the photovoltaic device was strongly improved， furthermore， the morpho-logy of the active layer also was finely tuned. Benefit from the enhanced open circuit voltage and fill factor， the ternary device results in an improved performance than its binary counterpart， giving a high power conversion efficiency of 17.72% with an open circuit voltage of 0.86 V， a short circuit current density of 26.99 mA/cm² and a fill factor of 76.34%. This work proves that introducing highly crystallized electron-deficient units into the small molecule donors third component is an effective way to improve the performance of ternary organic solar cells.



Z-configuration A-DA'D-A Type Acceptor with Thermal Annealing Induced High Open Circuit Voltage

ZHANG Liting, QIU Dingding, ZHANG Jianqi, LYU Kun, WEI Zhixiang

2023, 44(9):  20230164.  doi:10.7503/cjcu20230164

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The development of organic solar cells（OSCs） is approaching the industrial production gradation. In addition to high power conversion efficiency（PCE）， it is critical to develop new active layer materials with high open circuit voltage（V_OC） and to reduce non-radiative recombination loss. Here， “Z”-configured naphtho［1，2-c∶5，6-c'］bis［1，2，5］thiadiazole（NT） nuclear A-DA'D-A receptor（ZNT） with a high lowest unoccupied molecular orbital （LUMO） energy level， is developed based on the electron-withdrawing unit（A） -electron-donating unit（D） combination of A-DA'D-A type acceptor Y6， which emerges a “Z” configuration and achieves a reduction in the non-radiative recombination loss of the device with D18 as the donor by increasing the annealing temperature. In order to investigate the difference between this phenomenon and the general phenomenon of V_OC reduction by thermal annealing， the D18∶Y6 system was prepared as a reference. By increasing the temperature of thermal annealing， the Urbach energy（E_U） of D18∶Y6 is elevated， and the non-radiative recombination loss is increased， thus， the V_OC is consistently reduced. Surprisingly， the increase of the thermal annealing temperature decreases the E_U of D18∶ZNT and effectively decreases the non-radiative recombination loss， therefore， the V_OC shows an unexpected increase. V_OC increases from 0.950 V under the unannealed condition to 0.963 V（80 ℃）， 0.993 V（100 ℃）， and even 0.995 V（110 ℃）. Combining the trends of increasing electron mobility with decreasing crystal coherence length（CCL） of the pure acceptor ZNT when the annealing temperature increases， it is inferred that the reduction of energetic disorder is a result of the augmented order of the acceptor ZNT. In addition， the ZNT has a higher LUMO， higher occupied molecular orbital（HOMO） energy levels and band gap than Y6， higher planarity of structure， and lower device exciton dissociation， making the PCE of the ZNT-based devices lower than that of the Y6-based devices. The present work is potentially instructive for the development of A-DA'D-A type acceptors and provides a material design direction for the future development of high-V_OC OSCs that avoids the phenomenon of the reduction of V_OC by thermal annealing.



Simple Modulation of Side-chains of Near-infrared Absorbing Non-fullerene Acceptor for Higher Short-circuit Current Density

WANG Jiacheng, CAI Guilong, ZHANG Yajing, WANG Jiayu, LU Xinhui, ZHAN Xiaowei, CHEN Xingguo

2023, 44(9):  20230163.  doi:10.7503/cjcu20230163

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A long flexible side-chain of n-octyl group has been simultaneously introduced at indacenodithieno［3，2-b］thiophene（IDT） central core and （1，1-dicyanomethylene）rhodanine end-group to build a new “A-π-D-π-A” type non-fullerene acceptor（NFA）（JC11） with thiophene-fused benzothiadiazole（BTT） unit as a π-bridge， which has been proposed to investigate the influence of different side-chains at different sites of the same conjugated backbone on the properties. Compared with the previous reported acceptors A2 and JC1， the introduction of a suitable long alkyl side-chain of octyl groups at central core and terminal group not only endows JC11 to show more favorable intermolecular stacking， thus exhibiting more red-shifted absorption and better improved crystallinity than A1 with a more rigid and steric hexylphenyl group at central core， but also ensures its better solubility to avoid the poor phase-separation morphology in the blend film with PTB7-Th than JC1 with a short ethyl side-chain at end-group. Moreover， JC11 owns a higher molar extinction coefficient of up to 1.14×10⁵ L∙mol^-1∙cm^-1 and a higher electron mobility of 1.01×10^-3 cm²∙V^-1∙s^-1 as well as more balanced electron/hole mobilities（μ_e/μ_h=2.72） in the D/A blend film than A2 and JC1. Therefore， the optimized PTB7-Th∶JC11 based device achieves a more promising power conversion efficiency（PCE） of 10.09% with a much higher short circuit current density（J_SC） value of 24.20 mA/cm²， which greatly surpass the PCE of 8.20% and 8.16% with relatively low J_SC values of less than 20 mA/cm² for the optimized devices based on PTB7-Th∶A2 and PTB7-Th∶JC1， respectively. This work indicates that the regulation of side-chains is a simple but very effective strategy to improve the absorption and crystallization properties of the NFAs， thus resulting in higher J_SC and PCE for bulk heterojunction organic solar cells.



Cooperative Effect of Solvent Additive and Solvent Vapor Annealing on High-performance Thick-film Organic Solar Cells

YANG Hang, FAN Chenling, CUI Naizhe, LI Xiaoxiao, ZHANG Wenjing, CUI Chaohua

2023, 44(9):  20230162.  doi:10.7503/cjcu20230162

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The solvent additive 1-naphthalene（CN） and carbon disulfide（CS₂） solvent vapor annealing（SVA） were cooperatively used to optimize the thick-film active layer morphology based on the narrow band-gap small acceptors. The regulation mechanism of this strategy on the blend film morphology was revealed， and the effect of the strategy on the carrier dynamics as well as the photovoltaic performance of the device was investigated. The results show that the additive CN can effectively promote the crystallization and aggregation of the acceptor materials， and CS₂ solvent vapor annealing can further improve the molecular stacking properties of donor/acceptor materials， reduce the surface roughness of the blend film， and thus obtain good nano-scale phase separation morphology. Therefore， the charge transport and recombination properties of PM6∶Y6-based thick-film（300 nm） devices are effectively improved， thus obtaining the power conversion efficiency（PCE） of 15.23%， which is significantly higher than that of devices without additive treatment（PCE=11.75%） and CN-treated devices（PCE=13.48%）. Moreover， this strategy can also be used to optimize the PTQ10∶m-BTP-PhC6-based blend film morphology， and improve the photovoltaic performance of the devices from 13.22% to 16.92%.



Efficient Organic Solar Cells Based on Acceptor₁-acceptor₂ Type Polymer Donor

LI Hao, YANG Chenyi, LI Jiayao, ZHANG Shaoqing, HOU Jianhui

2023, 44(9):  20230157.  doi:10.7503/cjcu20230157

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In this work， we designed and synthesized two wide band-gap polymer donors： poly｛1，3-bis（2-ethylhexyl）-5-［5-（5'-methyl-4，4'-diundecyl-［2，2'-bithiazol］-5-yl）thiophen-2-yl］-7-（5-methylthiophen-2-yl）-4H，8H-benzo［1，2-c：4，5-c'］dithiophene-4，8-dione｝（PDTz-BDD） and poly（5-｛4，8-bis［5-（2-ethylhexyl）thiophen-2-yl］-6-methylbenzo［1，2-b：4，5-b'］dithiophen-2-yl｝-5'-methyl-4，4'-diundecyl-2，2'-bithiazole）（PDTz-BDT）. PDTz-BDT is a typical donor-acceptor（D-A） type copolymer， whereas PDTz-BDD is an acceptor₁-acceptor₂（A₁-A₂） type polymer. The photovoltaic properties of the two polymers were investigated by blending BTP-eC9 as the acceptor to construct organic solar cells， respectively. PDTz-BDD-based device achieves a higher power conversion efficiency of 10.36% due to its stronger light absorption ability， more obvious aggregation effect in solution and better morphological property of the blend film. This work not only demonstrates two novel donors， but also provides meaningful guidance for constructing A₁-A₂ type copolymers to develop efficient polymer donors in the future.



Enhancing the Performances of Porphyrin-based All-small-molecule Ternary Organic Solar Cells via Synergizing Fullerene and Non-fullerene Acceptors

WU Jifa, WU Hanping, YUAN Lin, PENG Xiaobin

2023, 44(9):  20230136.  doi:10.7503/cjcu20230136

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The introduction of a non-fullerene acceptor 2，2'-｛（2Z，2'Z）-［（4，4，9，9-tetrahexyl-4，9-dChemicalbookihydro-s-indaceno［1，2-b∶5，6-b'］dithiophene-2，7-diyl）bis（methanylylidene）］bis（3-oxo-2，3-dihydro-1H- indene-2，1-diylidene）｝dimalononitrile（IDIC） as the third component into a dimeric porphyrin small molecule donor（ZnP2-DPP） and fullerene acceptor ［6，6］-phenyl-C61-butyric acid methyl ester（PC₆₁BM） system achieved all-small molecule ternary organic solar cells（OSCs） with a power conversion efficiency（PCE） of 12.18%， which is higher than 9.47% for ZnP2-DPP∶PC₆₁BM binary cells and 8.82% for ZnP2-DPP∶IDIC binary OSCs. The addition of IDIC increased the absorption spectrum range and promoted the charge transfer between the three components， improving the photocurrents for the ternary solar cells. The synergy of the fullerene and non-fullerene acceptors effectively optimized the morphology of the blend film， and the molecular orientation was significantly tuned to form a hybrid orientation of face-on and edge-on， which led to a more favorable three-dimensional charge transport channels in the active layer and promotes the short-circuit current density（J_SC） and fill factor（FF）. This strategy exploited the advantages of both fullerene and non-fullerene acceptors， thus improving the four photovoltaic parameters of organic solar cells（OSCs）.



Aggregation Morphology of Perylene Bisimide Acceptors and the Role on Exciton Processes and Electron Transport in Organic Solar Cells

ZHANG Yu, CHEN Jiehuan, ZHOU Jiadong, LIU Linlin, XIE Zengqi

2023, 44(9):  20230092.  doi:10.7503/cjcu20230092

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Head-to-tail bonded perylene bisimide（PBI） dyads with different branched alkyl chains substituted at the terminal imide position show various stacking modes， which results in different effects on the excitonic processes and electron transportation. The dyad bearing branched alkyl chains with the branching sites close to the imide positions forms homogeneously amorphous state， while with branching sites being away from the imide positions the PBI core tend to stack with multiple modes. There are fewer energy trapping sites in the homogeneously amorphous state， but in the multiple stacking system the strong π-π interactions give more trapping sites. Our study demonstrates that the aggregation state of PBI-based acceptors plays an important role in the performances of organic solar cells（OSCs）. Multiple stacking needs to be diminished to avoid the constrained exciton dissociation and retarded charge transport in the active layer.