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The poor operational stability of non-fullerene electron acceptor (NFA) organic solar cells (OSCs) currently limits their commercial application. While previous studies have primarily focused on the degradation of the NFA component, we also consider here the electron donor material. We examine the stability of three representative donor polymers, PM6, D18, and PTQ10, paired with the benchmark NFA, Y6. After light soaking PM6 and D18 in air, we find an enhanced conversion of singlet excitons into trapped interchain polaron pairs on sub-100 femtosecond timescales. This process outcompetes electron transfer to Y6, significantly reducing the charge generation yield. However, this pathway is absent in PTQ10. We identify twisting in the benzo[1,2-b:4,5-b′]dithiophene (BDT)-thiophene motif shared by PM6 and D18 as the cause. By contrast, PTQ10 does not contain this structural motif and has improved stability. Thus, we show that the donor polymer can be a weak link for OSC stability, which must be addressed collectively with the NFA.

Recent advances in organic solar cells based on non-fullerene acceptors (NFAs) come with reduced non-radiative voltage losses (ΔVnr). Here we show that, in contrast to the energy-gap-law dependence observed in conventional donor:fullerene blends, the ΔVnr values in state-of-the-art donor:NFA organic solar cells show no correlation with the energies of charge-transfer electronic states at donor:acceptor interfaces. By combining temperature-dependent electroluminescence experiments and dynamic vibronic simulations, we provide a unified description of ΔVnr for both fullerene- and NFA-based devices. We highlight the critical role that the thermal population of local exciton states plays in low-ΔVnr systems. An important finding is that the photoluminescence yield of the pristine materials defines the lower limit of ΔVnr. We also demonstrate that the reduction in ΔVnr (for example

Non-fullerene organic solar cells (NFOSC) demonstrate record efficiencies exceeding 16%. In comparison with cells with the fullerene-based acceptor, the NFOSC benefit from a longer wavelength absor...

In contemporary organic solar cell (OSC) research, small A-D-A molecules comprising electron donor (D) and acceptor (A) units are increasingly used as a means to control the optoelectronic properties of photovoltaic blends. Slight structural variations to these A-D-A molecules can result in profound changes to the performance of the OSCs. Herein, we study two A-D-A molecules, BTCN-O and BTCN-M, which are identical in structure apart from a subtle difference in the position of alkyl chains, which force the molecules to adopt different equilibrium conformations. These steric effects cause the respective molecules to work better as an electron donor and acceptor when blended with benchmark acceptor and donor materials (PC71BM and PBDB-T). We study the photophysics of these “D:A” blends and devices using a combination of steady-state and time-resolved spectroscopic techniques. Time-resolved photoluminescence reveals the impact of the molecular conformation on the quenching of the A-D-A emission when BTCN-O and BTCN-M are blended with PBDB-T or PC71BM. Ultrafast broadband transient absorption spectroscopy demonstrates that the dynamics of charge separation are essentially identical when comparing BTCN-M and BTCN-O based blends, but the recombination dynamics are quite dissimilar. This suggests that the device performance is ultimately determined by the morphology of the blends imposed by the A-D-A conformation. This notion is supported by X-ray scattering data from the “D:A” films, and electroluminescence data and pump-push-photocurrent spectroscopy on the “D:A” devices. Our findings provide insight into the remarkable structure-function relationship in A-D-A molecules, and emphasize the need for careful morphological and energetic considerations when designing high-performance OSCs.

Due to the small dielectric constant of pristine conjugated polymers or small molecules, the photogenerated electron-hole pairs (excitons) are strongly bound because of Coulombic attraction, typically 0.2–0.5 eV (Brédas et al., 1996; Alvarado et al., 1998; and Arkhipov and Bässler, 2004) and are unable to dissociate automatically. The most effective way to solve the issue is to introduce another component possessing electron affinity into the photo-active film. The intermixing of electron donor (D) and electron acceptor (A) materials form the type II heterojunctions, where both highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the electron donor are higher than the electron acceptor. In particular, new interfacial electronic states between donor and acceptor are formed, called charge transfer (CT) states, where interesting optoelectronic processes, such as charge separation and recombination, take place (Benson-Smith et al., 2007).

The use of non-fullerene acceptors (NFAs) in organic solar cells has led to power conversion efficiencies as high as 18%1. However, organic solar cells are still less efficient than inorganic solar cells, which typically have power conversion efficiencies of more than 20%2. A key reason for this difference is that organic solar cells have low open-circuit voltages relative to their optical bandgaps3, owing to non-radiative recombination4. For organic solar cells to compete with inorganic solar cells in terms of efficiency, non-radiative loss pathways must be identified and suppressed. Here we show that in most organic solar cells that use NFAs, the majority of charge recombination under open-circuit conditions proceeds via the formation of non-emissive NFA triplet excitons; in the benchmark PM6:Y6 blend5, this fraction reaches 90%, reducing the open-circuit voltage by 60 mV. We prevent recombination via this non-radiative channel by engineering substantial hybridization between the NFA triplet excitons and the spin-triplet charge-transfer excitons. Modelling suggests that the rate of back charge transfer from spin-triplet charge-transfer excitons to molecular triplet excitons may be reduced by an order of magnitude, enabling re-dissociation of the spin-triplet charge-transfer exciton. We demonstrate NFA systems in which the formation of triplet excitons is suppressed. This work thus provides a design pathway for organic solar cells with power conversion efficiencies of 20% or more. A substantial pathway for energy loss in organic solar cells may be suppressed by engineering hybridization between non-fullerene acceptor triplet excitons and spin-triplet charge transfer excitons.

Revealing the charge generation is a crucial step to understand the organic photovoltaics. Recent development in non-fullerene organic solar cells (OSCs) indicates efficient charge separation even ...

Although significant improvements have been achieved for organic photovoltaic cells (OPVs), the top-performing devices still show power conversion efficiencies far behind those of commercialized solar cells. One of the main reasons is the large driving force required for separating electron-hole pairs. Here, we demonstrate an efficiency of 14.7% in the single-junction OPV by using a new polymer donor PTO2 and a nonfullerene acceptor IT-4F. The device possesses an efficient charge generation at a low driving force. Ultrafast transient absorption measurements probe the formation of loosely bound charge pairs with extended lifetime that impedes the recombination of charge carriers in the blend. The theoretical studies reveal that the molecular electrostatic potential (ESP) between PTO2 and IT-4F is large, and the induced intermolecular electric field may assist the charge generation. The results suggest OPVs have the potential for further improvement by judicious modulation of ESP.

A non-fullerene electron acceptor bearing a novel backbone with fused 10-heterocyclic ring (in-dacenodithiopheno-indacenodiselenophene), denoted by IDTIDSe-IC is developed for fullerene free polyme ...

A nonfullerene-based polymer solar cell (PSC) that significantly outperforms fullerene-based PSCs with respect to the power-conversion efficiency is demonstrated for the first time. An efficiency of >11%, which is among the top values in the PSC field, and excellent thermal stability is obtained using PBDB-T and ITIC as donor and acceptor, respectively.

To increase the lifetime of organic photovoltaic (OPV) devices and pass European lifetime standards, some encapsulation systems are often used to limit the exposition to oxygen and humidity of sola ...

Organic solar cells are thought to suffer from poor thermal stability of the active layer nanostructure, a common belief that is based on the extensive work that has been carried out on fullerene-based systems. We show that a widely studied non-fullerene acceptor, the indacenodithienothiophene-based acceptor ITIC, crystallizes in a profoundly different way as compared to fullerenes. Although fullerenes are frozen below the glass-transition temperature T-g of the photovoltaic blend, ITIC can undergo a glass-crystal transition considerably below its high T-g of similar to 180 degrees C. Nanoscopic crystallites of a low-temperature polymorph are able to form through a diffusion-limited crystallization process. The resulting fine-grained nanostructure does not evolve further with time and hence is characterized by a high degree of thermal stability. Instead, above T-g, the low temperature polymorph melts, and micrometer-sized crystals of a high-temperature polymorph develop, enabled by more rapid diffusion and hence long-range mass transport. This leads to the same detrimental decrease in photovoltaic performance that is known to occur also in the case of fullerene-based blends. Besides explaining the superior thermal stability of non-fullerene blends at relatively high temperatures, our work introduces a new rationale for the design of bulk heterojunctions that is not based on the selection of high-T-g materials per se but diffusion-limited crystallization. The planar structure of ITIC and potentially other non-fullerene acceptors readily facilitates the desired glass-crystal transition, which constitutes a significant advantage over fullerenes, and may pave the way for truly stable organic solar cells. We acknowledge financial support from the Knut and Alice Wallenberg Foundation through the project "Mastering Morphology for Solution-borne Electronics", the Swedish Research Council (grant agreement no. 2016-06146), and the Swedish Foundation for Strategic Research (grant agreement no. RMA15-0052). We thank the Cornell High Energy Synchrotron Source (CHESS), supported by the NSF under award DMR-1332208, for providing time for GIWAXS measurements. J.B. and K.V. acknowledge funding from the German Federal Ministry for Education and Research (BMBF) through the InnoProfile project "Organische p-i-n Bauelemente 2.2" (03IPT602X).

Small molecule donor/polymer acceptor bulk-heterojunction films with both compounds strongly absorbing have great potential for further enhancement of the performance of organic solar cells. By employing a newly synthesized small molecule donor with a commercially available polymer acceptor in a solution-processed fullerene-free system, a high power conversion efficiency of close to 4% is reported.

The stability of organic solar cells (OSCs) is critical for practical applications of this emerging technology. Unfortunately, in spite of intensive investigations, the degradation mechanisms in OSCs have not been clearly understood yet. In this report, we employ a range of spectroscopic and transport measurements, coupled with drift-diffusion modelling, to investigate the light-induced degradation mechanisms of fullerene-based OSCs. We find that trap states formed in the fullerene phase under illumination play a critical role in the degradation of the open-circuit voltage (V-OC) in OSCs. Our results indicate that the degradation is intrinsic to the fullerenes in OSCs and that alternative acceptor materials are desired for the development of stable OSCs. Funding Agencies|National Basic Research Program of China [2015CB932200]; Natural Science Foundation of Jiangsu [BK20140952, BK20150043]; National Natural Science Foundation of China [11474164, 61405091, 61634001]; European Union [2016YFE0112000]; Synergetic Innovation Center for Organic Electronics and Information Displays; National High Technology Research and Development Program of China [2011AA050520]; Jiangsu Specially-Appointed Professor program, Chinese Scholarship Council (CSC); Swedish Research Council (VR); European Commission SOLAR-ERA-NET; Swedish Energy Agency (Energimyndigheten); Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; Knut and Alice Wallenberg foundation (KAW)

In conjugated polymers and small molecules of organic solar cells, aggregation induced by intermolecular interactions governs the performance of photovoltaics. However, little attention has been paid to the connection between molecular structure and aggregation within solar cells based on soluble small molecules. Here we demonstrate modulation of intermolecular aggregation of two synthesized molecules through heteroatom substitution to develop an understanding of the role of aggregation in conjugated molecules. Molecule 1 (M1) based on 2-ethylhexyloxy-benzene substituted benzo[1,2-b:4,5-b′]dithiophene (BDTP) and diketopyrrolopyrrole (DPP) displays strong aggregation in commonly used organic solvents, which is reduced in molecule 2 (M2) by facile oxygen atom substitution on the BDTP unit confirmed by absorption spectroscopy and optical microscopy, while it successfully maintains molecular planarity and favorable charge transport characteristics. Solar cells based on M2 exhibit more than double the photocurrent of devices based on M1 and yield a power conversion efficiency of 5.5%. A systematic investigation of molecular conformation, optoelectronic properties, molecular packing and crystallinity as well as film morphology reveals structure dependent aggregation responsible for the performance difference between the two conjugated molecules.

We report a systematic study of the efficiency limitations of non-fullerene organic solar cells that exhibit a small energy loss (E-loss) between the polymer donor and the non-fullerene acceptor. To clarify the impact of Eloss on the performance of the solar cells, three thieno[3,4-c] pyrrole-4,6-dione-based conjugated polymers (PTPD3T, PTPD2T, and PTPDBDT) are employed as the electron donor, which all have complementary absorption spectra compared with the ITIC acceptor. The corresponding photovoltaic devices show that low Eloss (0.54 eV) in PTPDBDT: ITIC leads to a high open-circuit voltage (Voc) of 1.05 V, but also to a small quantum efficiency, and in turn photocurrent. The high Voc or small energy loss in the PTPDBDT-based solar cells is a consequence of less non-radiative recombination, whereas the low quantum efficiency is attributed to the unfavorable micro-phase separation, as confirmed by the steady-state and time-resolved photoluminescence experiments, grazing-incidence wide-angle X-ray scattering, and resonant soft X-ray scattering (R-SoXS) measurements. We conclude that to achieve high performance non-fullerene solar cells, it is essential to realize a large Voc with small Eloss while simultaneously maintaining a high quantum efficiency by manipulating the molecular interaction in the bulk-heterojunction. Funding Agencies|Ministry of science and technology [2016YFA0200700]; Recruitment Program of Global Youth Experts of China; National Natural Science Foundation of China [21574138, 91233205, 91633301]; Strategic Priority Research Program of the Chinese Academy of Sciences [XDB12030200]; Swedish Research Council [VR621-2013-5561]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [200900971]; Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]; Alexander-von-Humboldt foundation; King Abdullah University of Science and Technology (KAUST)

Manipulating charge generation in a broad spectral region has proved to be crucial for nonfullerene-electron-acceptor-based organic solar cells (OSCs). 16.64% high efficiency binary OSCs are achieved through the use of a novel electron acceptor AQx-2 with quinoxaline-containing fused core and PBDB-TF as donor. The significant increase in photovoltaic performance of AQx-2 based devices is obtained merely by a subtle tailoring in molecular structure of its analogue AQx-1. Combining the detailed morphology and transient absorption spectroscopy analyses, a good structure-morphology-property relationship is established. The stronger π-π interaction results in efficient electron hopping and balanced electron and hole mobilities attributed to good charge transport. Moreover, the reduced phase separation morphology of AQx-2-based bulk heterojunction blend boosts hole transfer and suppresses geminate recombination. Such success in molecule design and precise morphology optimization may lead to next-generation high-performance OSCs.

In recent years, fullerene bis-adducts have gained significant interest within the academic community due to their high-lying LUMO level. Herein, we carried out device optimization of the photovoltaic performances of novel photovoltaic polymer PBDTBDD with Bis-PCBM, and several characterization techniques including photoluminescence quench analysis, X-ray diffraction patterns, and atomic force microscopy were employed. As the synergistic result of balanced mobility, better crystallinity, efficient exciton dissociation, and charge transport efficiency, high fill factor and short-circuit current density as well as power conversion efficiency were achieved in the PBDTBDD/Bis-PCBM device. In addition, the optimized PSC device based on PBDTBDD:Bis-PCBM (1:1, wt/wt) with 3 vol % DIO yielded a high PCE of 6.07% with Voc of 1.00 V, Jsc of 10.02 mA/cm2, and FF of 60.54% under the illumination of AM1.5G, 100 mW/cm2. Therefore, we reported that polymer/Bis-PCBM-based polymer solar cells obtain both high efficiency ∼...

We demonstrate efficient polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) and fullerene derivatives ether Indene-C 60 Bisadduct (IC 60 BA) or Indene-C 70 Bisadduct (IC 70 BA)) by using solution-processed titanium(IV) oxide bis(2,4-pentanedionate) (TOPD) as electron collection layer (ECL) between the Al cathode and photoactive layer. The TOPD buffer layer was simply prepared by spin-coating isopropanol solution of TOPD on active layer and then baked at 80 °C for 15 min. The short-circuit current density ( J sc ) and the open-circuit voltage ( V oc ) of the devices can be simultaneously and significantly improved by optimizing the electron collection layer, the photoactive layer and the device fabrication conditions. The power conversion efficiency (PCE) of the P3HT:IC 60 BA BHJ device with TOPD buffer layer reaches 5.0% under the illumination of AM1.5G, 100 mW/cm 2 , which is increased by 27% in comparison with that (3.9%) of the device without TOPD buffer layer under the same experimental conditions. When IC 70 BA was chosen instead of IC 60 BA, the BHJ device could show better performance with PCE of 5.59%. The results indicate that TOPD is a promising electron collection layer for PSCs.

We report efficient and stable polymer solar cells (PSCs) based on poly(3-hexylthiophene) and various fullerene derivatives using solution processed, cost effective molybdenum oxide (s-MoOx) as an anode interfacial layer. The chemical structure of the obtained s-MoOx was characterized by FTIR and XPS. The s-MoOx layer exhibits high light transmittance and effective hole collection properties. The PSCs with the s-MoOx anode buffer layer show enhanced performance in comparison with PEDOT:PSS modified devices. The power conversion efficiency of the PSC based on P3HT:IC70BA with the s-MoOx anode buffer layer reached 6.57% under an illumination of AM1.5G at 100 mW cm−2. In addition, compared with PEDOT:PSS modified devices, PSCs with the s-MoOx anode buffer layer exhibit a much superior stability and longer lifetime.

Fast and efficient charge separation is essential to achieve high power conversion efficiency in organic solar cells (OSCs). In state-of-the-art OSCs, this is usually achieved by a significant driv ...

A new conjugated polymer based on 5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione, named as PBDTBDD, was designed, synthesized, and applied in polymer solar cells (PSCs). A power conversion efficiency (PCE) of 6.67% was obtained from the PBDTBDD/PC61BM-based PSC, which is a remarkable result for the PSCs using PC61BM as electron acceptor. The PBDTBDD/PC61BM-based device exhibits a narrow absorption band and excellent quantum efficiency in the range from 500 to 700 nm. Furthermore, PBDTBDD shows a strong aggregation effect in solution state, and the study indicates that although the temperature used in solution preparation has little influence on molecular orientation as well as crystallinity of the D/A blend, it plays an important role in forming proper domain size in the blend. This work provides a good example to reveal the correlation between the morphology of the blend films and the processing temperature of the solution preparation. Furthermore, the study in this work suggests an intere...

We demonstrate efficient inverted polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) by using solution-processed titanium(IV) oxide bis(2,4-pentanedionate) (TOPD) as electron collection layer (ECL) between the indium tin oxide (ITO) electrode and photoactive layer. The TOPD buffer layer was prepared by spin-coating isopropanol solution of TOPD on ITO and then baked at 140 °C for 5 min. The power conversion efficiency (PCE) of the inverted PSC with TOPD buffer layer reaches 4% under the illumination of AM1.5G, 100 mW/cm 2 , which is increased by 76% in comparison with that (2.27%) of the inverted device without TOPD ECL. The results indicate that TOPD is a promising electron collection layer for inverted PSCs.

WO3 is an effective anode buffer layer to substitute PEDOT:PSS in both organic light-emitting diodes and polymer solar cells (PSCs). However, the vacuum deposition of the WO3 layer is not compatibl...

We report polymer solar cells (PSCs) based on poly(3-hexylthiophene (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) using water-soluble nickel acetate (Ni(CH3COO)2, NiAc) instead of acidic poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS) as hole collection layer (HCL) between the indium tin oxide (ITO) electrode and photoactive layer. The NiAc layer can effectively decrease Rs and increase Rp and shows effective hole collection property. Under the illumination of AM1.5G, 100 mW/cm2, the short-circuit current density (Jsc) of the NiAc based device (ITO/NiAc/P3HT : PCBM/Ca/Al) reach 11.36 mA/cm2, which is increased by 11% in comparison with that (10.19 mA/cm2) of PEDOT : PSS based device (ITO/PEDOT : PSS/P3HT : PCBM/Ca/Al). The power conversion efficiency of the NiAc based devices reach 3.76%, which is comparable to that (3.77%) of the device with PEDOT : PSS HCL under the same experimental conditions. Moreover, NiAc based PSCs show superior long-term stability than PEDOT : PSS based PSCs. Our work gives a new option for HCL selection in designing more stable PSCs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Two random copolymers of phenylene vinylene and pyridinylene vinylene, ED-co-PyV-PPV and EM-co-PyV-PPV, were synthesized according to the Gilch route. The polymers possess good solubility in common solvents, and high thermal stability with 5% weight loss temperature above 378°C. The weight-average molecular weight (Mw) and polydispersity index of ED-co-PyV-PPV and EM-co-PyV-PPV are 3.12 × 105 and 1.40, and 2.30 × 105 and 1.96, respectively. Single-layer polymer light-emitting diodes (PLEDs) with indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT):poly(styrenesulfonate) (PSS)/polymer/Ca/Al configuration were fabricated. The turn-on voltages of the PLEDs based on ED-co-PyV-PPV and EM-co-PyV-PPV were approximately 4.0 V and 2.8 V, respectively. The ED-co-PyV-PPV PLED device exhibited the maximum luminance of ca. 4380 cd/m2 with maximum electroluminescence (EL) efficiency of 6.35 cd/A.

High-performance inverted polymer solar cells (PSCs) with solution-processed titanium chelate TIPD as electron collecting layer are reported. The power conversion efficiency (PCE) of the inverted PSC with a-TIPD buffer layer with thermal annealing at 150 °C for 10 min reached 7.4% under the illumination of AM1.5, 100 mW/cm(2), which is increased by 16% in comparison with that (6.4%) of the device in the conventional structure. The PCE of 7.4% is the highest among the inverted PSCs reported so far in the literature.

The effects of composition on the performance of hybrid photovoltaic cells based on PbSe nanocrystal quantum dot(NQD)/ poly(3-hexylthiophene) nanocomposites were studied. The device performance and the absorption property strongly depended on the loading of PbSe. To improve the device performance, a pure light-absorbing P3HT film was inserted underneath the blended layer of P3HT and PbSe nanocrystal quantum dots in the active region. Such a design allowed for the employment of a thinner bulk heterojunction for more efficient carrier collection without an excessive reduction of the overall light absorption by the photovoltaic cell. The measured device performance showed a significant improvement over previously reported hybrid cells containing bulk heterojunctions of P3HT and Pb(S,Se) nanocrystal quantum dots.

The voltage loss, determined by the difference between the optical gap (E-g) and the open-circuit voltage (V-OC), is one of the most important parameters determining the performance of organic solar cells (OSCs). However, the variety of different methods used to determine E-g makes it hard to fairly compare voltages losses among different material systems. In this paper, the authors discuss and compare various E-g determination methods and show how they affect the detailed calculation of voltage losses, as well as predictions of the maximum achievable power conversion efficiency. The aim of this paper is to make it possible for the OSC community to compare voltage losses in a consistent and reasonable way. It is found that the voltage losses for strongly absorbed photons in state-of-the-art OSCs are not much less than 0.6 V, which still must be decreased to further enhance efficiency. Funding Agencies|Swedish Research Council VR [2017-00744]; Swedish Energy Agency Energimyndigheten [2016-010174]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; DFG [KI-1571/2-1]; China Scholarship Council

In this study, the optical, electrochemical, electrolumiscent, and photovoltaic properties of a series of poly(p-phenylene vinylene) (PPV) derivatives bearing different dendritic pendants, poly{2-[3(,5(-bis(2 00 -ethylhexyloxy)benzyloxy]-1,4phenylenevinylene} (BE-PPV), poly{2-[2(,5(-bis(3 00 ,7 00 -dimethyl)octyloxy]-1,4-phenylenevinylene} (BD-PPV), poly[2methoxy-5-(2(-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), poly{2-[3(,5(-bis(2 00 -ethylhexyloxy)benzyloxy]-1,4phenylenevinylene}-co-poly[2-methoxy-5-(2(-ethylhexyloxy)-1,4-phenylenevinylene] (BE-co-MEH-PPV), and poly{2-[2(, 5(-bis(3 00 ,7 00 -dimethyl)octyloxy]-1,4-phenylenevinylene}-co-poly[2-methoxy-5-(3(,7(- dimethyloctyloxy)-1,4-phenylenevinylene] (BD-co-MDMO-PPV), were investigated. The steric pendants strongly affect the absorption spectra, photoluminescence (PL) sepctra, the onset oxidation/reduction potentials, and further affect the electrolumiscent and photovoltaic properties. Copolymerization can reduce the steric effect and improve the electrolumiscent and photovoltaic properties. The brightness of light-emitting diodes base on copolymer BE-co-MEH-PPV and BD-co-MDMO-PPV reached 3988 and 3864cd/m 2 , respectively, much higher than that based on homopolymer BE-PPV (523cd/m 2 ) and BD-PPV (333cd/m 2 ), also higher than that based on MEH-PPV (3788cd/m 2 ). The power conversion efficiency (PCE) of solar cells based on BE-co-MEH-PPV and BD-co-MDMO-PPV reached 1.41, 0.76%, respectively, much higher than that based on BE-PPV (0.24%) and BD-PPV (0.14%). Copyright 2010 John Wiley & Sons, Ltd.

Low-work-function active metals are commonly used as cathode in polymer solar cells (PSCs), but sensitivity of the active metals towards moisture and oxygen results in poor stability of the devices. Therefore, solution-proceessable and stable cathode buffer layer is of great importance for the application of PSCs. Here we demonstrate high performance PSCs by employing as-prepared zirconium acetylacetonate (a-ZrAcac) film spin-cast from its ethanol solution as cathode buffer layer. The PSCs based on a low bandgap polymer PBDTBDD as donor and PC60BM as acceptor with a-ZrAcac/Al cathode demonstrated an average power conversion efficiency (PCE) of 8.75% which is significantly improved than that of the devices with traditional Ca/Al cathode. The improved photovoltaic performance is benefitted from the decreased series resistance and enhanced light harvest of the PSCs with the a-ZrAcac/Al cathode. The results indicate that a-ZrAcac is a promising high performance cathode buffer layer for fabricating large area flexible PSCs.

An integrated device architecture was constructed via vertical combination of planar and bulk heterojunctions by solution processing, where a cross-linked D-A copolymer (PBDTTT-Br25) was inserted between a PEDOT:PSS layer and the blended photoactive layer. PBDTTT-Br25 can readily undergo photo crosslinking to form an insoluble robust film via ultraviolet irradiation after solution-deposition, which enables the subsequent solution processing of a photoactive layer on the robust surface. The insertion of a pure PBDTTT-Br25 layer to build an integrated heterojunction could provide an additional donor/acceptor interface, which enables hole transport to the anode without interruption, thereby reducing the charge carrier recombination probability. The power conversion efficiency (PCE) of the polymer solar cell (PSC) with the integrated architecture reaches 5.24% under an AM1.5G illumination of 100 mW/cm(2), which is increased by 65%, in comparison with that of the reference single heterojunction device (3.17%), under the same experimental conditions.

A novel polythiophene derivative, PBT1, was designed, synthesized, and applied in polymer solar cells (PSCs). This work provides a successful example of using molecular structure as a tool to realize optimal photovoltaic performance with high polymer content, thus enabling the realization of efficient photoabsorption in very thin films. As a result, an efficiency of 6.88% was recorded in a PSC with a 75 nm active layer.

A solution-processed vanadium oxide (s-VO(x)) anode buffer layer on an indium-tin-oxide (ITO) electrode was used instead of PEDOT:PSS for improving the stability and photovoltaic performance of the polymer solar cells (PSCs). The s-VO(x) layer was prepared by spin-coating a vanadyl acetylacetonate (VO(acac)(2)) isopropyl alcohol solution on the ITO electrode and then thermal annealing at 150 °C for 10 min. The s-VO(x) oxide layer is highly transparent in the visible range and shows effective hole collection property. The photovoltaic performance of the s-VO(x) buffer layer was studied by fabricating the PSCs based on poly(3-hexylthiophene) (P3HT) as an electron donor and four soluble fullerene derivatives, [6,6]-phenyl-C(61)-butyric acid methyl ester (PC(60)BM), [6,6]-phenyl-C(71)-butyric acid methyl ester (PC(70)BM), indene-C(60) bisadduct (IC(60)BA), and indene-C(70) bisadduct (IC(70)BA), as electron acceptors. The PSCs with the s-VO(x) buffer layer show improved performance in comparison with the traditional devices with the PEDOT:PSS buffer layer on ITO, no matter which fullerene derivative was used as an acceptor. The power conversion efficiency of the PSC based on P3HT:IC(70)BA (1 : 1, w/w) with the s-VO(x) anode buffer layer reached 6.35% under the illumination of AM1.5G 100 mW cm(-2).

In recent 20 years, the city of Wuhan has built a big high-tech industry cluster which is named Optics Valley of China. The Optics Valley of China is developing quickly, but scarcity of talent has become the bottleneck for its development. Recruiting talented worker is significant concern and the influence factors of talent flow have been explored. The questionnaire about influence factor of talent flow are designed and sent to 20 core enterprises at Optics Valley of China. 178 high-tech specialists returned the effective answer sheet. In the questionnaire survey, principal components analysis is used to explore the structure of this instrument, which suggests six components: working environment, industry cluster characteristic, urban environment, income, individual development, value and personality. The investigation result demonstrates the top three of these components are income, working environment, value and personality. The result verified the influence factor structure's application in high-tech industry cluster, but it also shows the difference based on high-tech industry's speciality.

A series of triphenylamine-based small molecule organic hole transport materials (HTMs) with low crystallinity and high hole mobility are systematically investigated in solid-state dye-sensitized s ...

We report efficient inverted polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) using alcohol-soluble titanium (diisopropoxide) bis (2,4-pentanedionate) (TIPD) as an electron selective layer between the indium tin oxide (ITO) electrode and the photoactive layer. The thermally annealed TIPD layer is highly transparent in the visible range and shows effective electron collection ability. By optimizing the electron-collecting layer, the photoactive layer and the hole-collecting layer, the power conversion efficiency (PCE) of the inverted device with the structure ITO/TIPD/P3HT : PCBM/MoO3/Ag reaches 4.10% under the illumination of AM1.5G, 100 mW cm−2, which is among the highest values for inverted PSCs based on P3HT : PCBM. The PCE of the inverted device is improved in comparison with the conventional device (3.77%) under the same experimental conditions.

We report efficient polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) and indene-C(60) bisadduct (ICBA) with water soluble nickel acetate (NiAc) instead of acidic poly(ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS) as hole collection layer (HCL). The NiAc layer after thermal annealing at 150 °C for 30 min (α-NiAc) shows high transparency with light transmittance better than PEDOT : PSS in the wavelength range of 500-900 nm, high hole mobility of 1.3 × 10(-3) cm(2) V(-1) s(-1) and suitable energy levels for application as HCL. The power conversion efficiency of the PSC based on P3HT/ICBA with the α-NiAc anode buffer layer reached 6.08% under the illumination of AM1.5G 100 mW cm(-2), which is among the best efficiencies of the P3HT-based PSCs. This work gives a new option for HCL selection in designing higher efficiency and more stable PSCs.

Fullerene-based polymer solar cells (PSCs), namely utilizing polymers as electron donors and fullerene derivatives as electron acceptors, have been the subject of organic photovoltaic and the predominant type of polymer solar cells in the past decade. [ 1–6 ] Although fullerene derivatives like [6,6]-phenylC 61 (or C 71 )-butyric acid methyl ester (PC 61 BM or PC 71 BM) have made great success, they still have several drawbacks, including poor absorption of visible light for PC 61 BM and high cost for PC 71 BM, which limit their practical applications. [ 7 ] In contrast, non-fullerene acceptors can be easily produced in large scale at low cost and chemically modifi ed with highly tunable absorption spectra and energy levels than those of fullerene derivatives. [ 8,9 ] Encouragingly, Facchetti et al. [ 10 ] reported a record power conversion effi ciency (PCE) of ≈6.4% in polymer:polymer blend-based PSCs, which demonstrated the great potential of fullerene-free PSCs and signifi cantly promoted the research in the fi eld. Beyond polymers, [ 11–16 ] a variety of non-fullerene small molecules [ 17–32 ]

The open-circuit voltage of organic solar cells is usually lower than the values achieved in inorganic or perovskite photovoltaic devices with comparable bandgaps. Energy losses during charge separation at the donor–acceptor interface and non-radiative recombination are among the main causes of such voltage losses. Here we combine spectroscopic and quantum-chemistry approaches to identify key rules for minimizing voltage losses: (1) a low energy offset between donor and acceptor molecular states and (2) high photoluminescence yield of the low-gap material in the blend. Following these rules, we present a range of existing and new donor–acceptor systems that combine efficient photocurrent generation with electroluminescence yield up to 0.03%, leading to non-radiative voltage losses as small as 0.21 V. This study provides a rationale to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells. Key optoelectronic properties for donor and acceptor organic semiconductors are identified to obtain organic solar cells with reduced open-circuit voltage losses and high power conversion efficiencies.