Enhanced efficiency of ternary organic solar cells by doping a polymer material in P3HT:PC61BM

Doping a low‐bandgap polymer material (PDTBDT‐DTNT) as a complementary electron donor in poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C₆₁‐butyricacid methyl ester (PC₆₁BM) blend is experimented to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The PCE of OSCs was increased from 3.19% to 3.75% by doping 10 wt% PDTBDT‐DTNT, which was 17.55% higher than that of the OSCs based on binary blend of P3HT:PC₆₁BM (host cells). The short‐circuit current density (J_sc) was increased to 10.11 mA·cm⁻² compared with the host cells. Although the PCE improvement could partly be attributed to more photon harvest for complementary absorption of 2 donors by doping appropriate PDTBDT‐DTNT, the promotion of charge separation and transport as well as the suppression of charge recombination due to a matrix of cascade energy levels is also important. And the better morphology of the active layer films is beneficial to the optimized performance of ternary devices.     

退火处理提高P3HT:PCBM聚合物太阳能电池光伏性能

利用旋转涂膜方法制备了以P3HT:PCBM为有源层的聚合物太阳能电池, 器件结构为ITO/PEDOT:PSS/P3HT:PCBM/Al(氧化铟锡导电玻璃/聚二氧乙基噻吩:聚对苯乙烯磺酸/聚三已基噻酚:富勒烯衍生物/铝),研究了退火温度对聚合物太阳能电池性能的影响. 实验发现: 聚合物薄膜经过120 °C退火10 min处理后, 开路电压(V_oc)达到0.64 V, 短路电流密度(J_sc)为10.25 mA·cm^-2, 填充因子(FF) 38.1%, 光电转换效率(PCE)达到2.00%. 为了讨论其内在机制, 对不同退火条件下聚合物薄膜进行了各种表征. 从紫外-可见吸收光谱中发现, 退火处理使P3HT在可见光范围内吸收加强且吸收峰展宽, 特别是在560和610 nm处的吸收强度明显增大; X射线衍射(XRD)结果表明, 120 °C退火后P3HT在(100)晶面上的衍射强度是未退火薄膜的2.8倍, 有利于光生载流子的输运; 原子力显微镜(AFM)研究结果表明, 退火显著增大了P3HT与PCBM的相分离程度, 提高了激子解离的几率; 傅里叶变换红外(FTIR)光谱验证了退火并没有引起聚合物材料物性的变化.     

Enhanced properties of photovoltaic devices tailored with novel supramolecular structures based on reduced graphene oxide nanosheets grafted/functionalized with thiophenic materials

For verifying the influence of donor–acceptor supramolecules on photovoltaic properties, different hybrids were designed and used in organic solar cells. In this respect, reduced graphene oxide (rGO) was functionalization with 2‐thiophene acetic acid (rGO‐f‐TAA) and grafted with poly(3‐dodecylthiophene) (rGO‐g‐PDDT) and poly(3‐thiophene ethanol) (rGO‐g‐PTEt) to manipulate orientation of poly(3‐hexylthiophene) (P3HT) assemblies. Face‐on, edge‐on, and flat‐on orientations were detected for assembled P3HTs on rGO and its functionalized and grafted derivatives, respectively. Alteration of P3HT orientation from face‐on to flat‐on enhanced current density (J _sc), fill factor (FF), and power conversion efficiency (PCE) and thus J _sc = 7.11 mA cm^?2, FF = 47%, and PCE = 2.14% were acquired. By adding phenyl‐C71‐butyric acid methyl ester (PC71BM) to active layers composed of pre‐designed P3HT/rGO, P3HT/rGO‐f‐TAA, P3HT/rGO‐g‐PDDT, and P3HT/rGO‐g‐PTEt hybrids, photovoltaic characteristics further improved, demonstrating that supramolecules appropriately mediated in P3HT:PC71BM solar cells. Phase separation was more intensified in best‐performing photovoltaic systems. Larger P3HT crystals assembled onto grafted rGOs (95–143 nm) may have acted as convenient templates for the larger and more intensified phase separation in P3HT:PCBM films. The best performances were reached for P3HT:P3HT/rGO‐g‐PDDT:PCBM (J _sc = 9.45 mA cm^?2, FF = 54%, and PCE = 3.16%) and P3HT:P3HT/rGO‐g‐PTEt:PCBM (J _sc = 9.32 mA cm^?2, FF = 53%, and PCE = 3.11%) photovoltaic systems. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1877–1889     

Random poly(3‐hexylthiophene‐co‐3‐cyanothiophene‐co‐3‐(2‐ethylhexyl)thiophene) copolymers with high open‐circuit voltage in polymer solar cells

For the purpose of developing poly(3‐hexylthiophene) (P3HT) based copolymers with deep‐lying highest occupied molecular orbital (HOMO) levels for polymer solar cells with high open‐circuit voltage (V_oc), we report a combined approach of random incorporation of 3‐cyanothiophene (CNT) and 3‐(2‐ethylhexyl)thiophene (EHT) units into the P3HT backbone. This strategy is designed to overcome CNT content limitations in recently reported P3HT‐CNT copolymers, where incorporation of more than 15% of CNT into the polymer backbone leads to impaired polymer solubility and raises the HOMO level. This new approach allows incorporation of a larger CNT content, reaching even lower‐lying HOMO levels. Importantly, a very low HOMO level of ?5.78 eV was obtained, representing one of the lowest HOMO values for exclusively thiophene‐based polymers. Lower HOMO levels result in higher V_oc and higher power conversion efficiencies (PCE) compared to the previously reported P3HT‐CNT copolymers containing only 3‐hexylthiophene and CNT units. As a result, solar cells based on P3HT‐CNT‐EHT(15:15) , which contains 70% of P3HT, 15% of CNT and 15% of EHT, yield a V_oc of 0.83 V in blends with PC₆₁BM while preserving high fill factor (FF) and high short‐circuit current density (J_sc), resulting in 3.6% PCE. Additionally, we explored the effect of polymer number‐average molecular weight (M_n) on the optoelectronic properties and solar cell performance for the example of P3HT‐CNT‐EHT(15:15). The organic photovoltaic (OPV) performance improves with polymer M_n increasing from 3.4 to 6.7 to 9.6 kDa and then it declines as M_n further increases to 9.9 and to 16.2 kDa. The molecular weight study highlights the importance of not only the solar cell optimization, but also the significance of individual polymer properties optimization, in order to fully explore the potential of any given polymer in OPVs. The broader ramification of this study lies in potential application of these high band gap copolymers with low‐lying HOMO level in the development of ternary blend photovoltaics as well as tandem OPV. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1526–1536     

Effect of Device Fabrication Conditions on Photovoltaic Performance of Polymer Solar Cells Based on Poly(3‐hexylthiophene) and Indene‐C70 Bisadduct

Effect of the device fabrication conditions on photovoltaic performance of the polymer solar cells based on poly(3‐hexylthiophene) (P3HT) as donor and indene‐C₇₀ bisadduct (IC₇₀BA) as acceptor was studied systematically. The device fabrication conditions we studied include pre‐thermal annealing temperature, active layer thickness, and the P3HT:IC₇₀BA weight ratios. For devices with a 188‐nm‐thick active layer of P3HT:IC₇₀BA (1:1, w:w) blend film and pre‐thermal annealing at 150°C for 10 min, maximum power conversion efficiency (PCE) reached 5.82% with V_oc of 0.81 V, I_sc of 11.37 mA/cm², and FF of 64.0% under the illumination of AM1.5G, 100 mW/cm².     

用CdSe/ZnS量子点提高体异质结有机太阳电池的效率

通过掺杂吸收光谱在可见光波段的量子点可提高聚合物对可见光的吸收,因此掺杂CdSe/ZnS核-壳结构量子点(CQDs)能提高聚(3-己基噻吩):[6,6]-苯基-C61-丁酸甲酯(P3HT:PCBM)体异质结太阳电池的能量转换效率.本文研究了CdSe/ZnS量子点在P3HT:PCBM中的不同掺杂比例及其表面配体对太阳电池光伏性能的影响,优化器件ITO(氧化铟锡)/PEDOT:PSS(聚(3,4-乙撑二氧噻吩:聚苯乙烯磺酸)/P3HT:PCBM:(CdSe/ZnS)/Al的能量转换效率达到了3.99%,与相同条件下没有掺杂量子点的参考器件ITO/PEDOT:PSS/P3HT:PCBM/Al相比,其能量转换效率提高了45.1%.     

Compositional dependence of the open-circuit voltage in ternary blend bulk heterojunction solar cells based on two donor polymers

Ternary blend bulk heterojunction (BHJ) solar cells containing as donor polymers two P3HT analogues, high-band-gap poly(3-hexylthiophene-co-3-(2-ethylhexyl)thiophene) (P3HT(75)-co-EHT(25)) and low-band-gap poly(3-hexylthiophene-thiophene-diketopyrrolopyrrole) (P3HTT-DPP-10%), with phenyl-C(61)-butyric acid methyl ester (PC(61)BM) as an acceptor were studied. When the ratio of the three components was varied, the open-circuit voltage (V(oc)) increased as the amount of P3HT(75)-co-EHT(25) increased. The dependence of V(oc) on the polymer composition for the ternary blend regime was linear when the overall polymer:fullerene ratio was optimized for each polymer:polymer ratio. Also, the short-circuit current densities (J(sc)) for the ternary blends were bettter than those of the binary blends because of complementary polymer absorption, as verified using external quantum efficiency measurements. High fill factors (FF) (>0.59) were achieved in all cases and are attributed to high charge-carrier mobilities in the ternary blends. As a result of the intermediate V(oc), increased J(sc) and high FF, the ternary blend BHJ solar cells showed power conversion efficiencies of up to 5.51%, exceeding those of the corresponding binary blends (3.16 and 5.07%). Importantly, this work shows that upon optimization of the overall polymer:fullerene ratio at each polymer:polymer ratio, high FF, regular variations in V(oc), and enhanced J(sc) are possible throughout the ternary blend composition regime. This adds to the growing evidence that the use of ternary blends is a general and effective strategy for producing efficient organic photovoltaics manufactured in a single active-layer processing step.     

Significance of miscibility in multidonor bulk heterojunction solar cells

Ternary organic blends have potential in realizing efficient bulk heterojunction (BHJ) organic solar cells by harvesting a larger portion of the solar spectrum than binary blends. Several challenging requirements, based on the electronic structure of the components of the ternary blend and their nanoscale morphology, need to be met in order to achieve high power conversion efficiency in ternary BHJs. The properties of a model ternary system comprising two donor polymers, poly(3-hexylthiophene) (P3HT) and a furan-containing, diketopyrrolopyrrole-thiophene low-bandgap polymer (PDPP2FT), with a fullerene acceptor, PC₆₁BM, were examined. The relative miscibility of PC₆₁BM with P3HT and PDPP2FT was examined using diffusion with dynamic secondary ion mass spectrometry (dynamic SIMS) measurements. Grazing incidence small and wide angle X-ray scattering analysis (GISAXS and GIWAXS) were used to study the morphology of the ternary blends. These measurements, along with optoelectronic characterization of ternary blend solar cells, indicate that the miscibility of the fullerene acceptor and donor polymers is a critical factor in the performance in a ternary cell. A guideline that the miscibility of the fullerene in the two polymers should be matched is proposed and further substantiated by examination of known well-performing ternary blends. The ternary blending of semiconducting components can improve the power conversion efficiency of bulk heterojunction organic photovoltaics. The blending of P3HT and PDPP2FT with PC₆₁BM leads to good absorptive coverage of the incident solar spectrum and cascading transport energy levels. The performance of this ternary blend reveals the impact of the miscibility of PC₆₁BM in each polymer as a function of composition, highlighting an important factor for optimization of ternary BHJs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 237–246     

Designing Nonfullerene Acceptors with Oligo(Ethylene Glycol) Side Chains: Unraveling the Origin of Increased Open-Circuit Voltage and Balanced Charge Carrier Mobilities

Despite the recent rapid development of organic solar cells (OSCs), the low dielectric constant (ϵ_r=3–4) of organic semiconducting materials limits their performance lower than inorganic and perovskite solar cells. In this work, we introduce oligo(ethylene glycol) (OEG) side chains into the dicyanodistyrylbenzene-based non-fullerene acceptors (NIDCS) to increase its ϵ_r up to 5.4. In particular, a NIDCS acceptor bearing two triethylene glycol chains (NIDCS-EO3) shows V_OC as high as 1.12 V in an OSC device with a polymer donor PTB7, which is attributed to reduced exciton binding energy of the blend film. Also, the larger size grain formation with well-ordered stacking structure of the NIDCS-EO3 blend film leads to the increased charge mobility and thus to the improved charge mobility balance, resulting in higher J_SC, FF, and PCE in the OSC device compared to those of a device using the hexyl chain-based NIDCS acceptor (NIDCS-HO). Finally, we fabricate NIDCS-EO3 devices with various commercial donors including P3HT, DTS-F, and PCE11 to show higher photovoltaic performance than the NIDCS-HO devices, suggesting versatility of NIDCS-EO3.     

Bay‐annulated indigo based near‐infrared sensitive polymer for organic solar cells

A new conjugated polymer (PBAIIDTT) based on bay‐annulated indigo and indacenodithieno[3,2‐b]thiophene was designed, synthesized, and characterized. PBAIIDTT shows strong absorption in 400–500 and 600–800 nm, and its HOMO and LUMO energy levels are −5.45 eV and −3.65 eV, respectively. In organic field‐effect transistors, the polymer exhibits a relatively high hole mobility of 0.39 cm² V⁻¹ s⁻¹. PBAIIDTT was added to poly(3‐hexylthiophene) (P3HT) and phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) based organic solar cells. Ternary blend solar cells with 10% PBAIIDTT show an increased short circuit current density due to the broadened photocurrent generated in the near‐infrared region, and a power conversion efficiency of 3.78%, which is higher than that of the P3HT:PC₆₁BM binary control devices (3.33%). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 213–220     

Isothermal crystallization of P3HT:PCBM blends studied by RHC

Defining appropriate annealing temperatures and times is vitally important for increasing the efficiency of bulk heterojunction solar cells by favoring the crystallinity of the polymer-fullerene blend components. In order to better understand the annealing process, the isothermal crystallization of poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) blend investigated by means of rapid heating cooling calorimetry (RHC). Isothermal crystallization experiments at temperatures in between the glass transition and melting, within the temperature range of 70–150 °C, can successfully be performed since RHC permits cooling at a sufficiently high rate in order to prevent crystallization during cooling. Crystallization isotherms were determined from the subsequent melting behavior of the blend. They were measured for a wide set of annealing temperatures and times, and the evolution of the crystallization rate with temperature is compared for annealing from the glassy state and from the melt state.     

Decreased domain size and improved crystallinity by adjusting solvent–polymer interaction parameters in all‐polymer solar cells

We have investigated the effect of solvent–polymer interaction on the morphology, crystallinity, and device performance of poly‐(3‐hexylthiophene) (P3HT) and poly{2,7‐(9,9‐didodecyl‐fluorene)‐alt‐5,5‐[4′,7′‐bis(2‐thienyl)‐2′,1′,3′‐benzothia‐diaole]} (PF12TBT) blend system. 3‐Hexylthiophene (3‐HT), which had the similar structural units with both donor and acceptor materials, was chosen as the solvent additive to be added into the main solvent chlorobenzene (CB), to adjust the solvent–polymer interaction. With the 3‐HT percentage increasing from 5 to 30% in CB solution, the solvent–polymer interaction between polymer and solvent molecules decreased slightly according to the calculated solubility parameters (δ) and interaction parameters (χ₁₂). As a result, nanoscale phase‐separated and interconnected morphology with decreased domain size of both donor and acceptor was formed. Meanwhile, the order of P3HT molecule was enhanced which resulted from the extended film drying time and increased molecular planarity after incorporation of 3‐HT. The power conversion efficiency (PCE) had a gradual improvement to 1.08% as the 3‐HT percentage reached 10%, which can be attributed to the enhanced short‐circuit current (J_sc) and fill factor (FF). However, when the 3‐HT percentage exceeded 20%, the decreased J_sc and FF ultimately decreased the PCE. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 288–296     

New Conjugated Molecules with Two and Three Dithienyldiketopyrrolopyrrole (DPP) Moieties Substituted at meta Positions of Benzene toward p‐ and n‐Type Organic Photovoltaic Materials

Two conjugated molecules, TADPP3 and TADPP2‐TT , are reported, in which three and two dithienyldiketopyrrolopyrrole (DPP) moieties, respectively, are substituted at the meta positions of benzene. Based on cyclic voltammetry and absorption data, TADPP3 and TADPP2‐TT possess similar HOMO and LUMO energies of about ?5.2 and ?3.4 eV, respectively. Thin films of TADPP3 and TADPP2‐TT exhibit p‐type semiconducting behavior with hole mobilities of 2.36×10^?3 and 3.76×10^?4 cm² V^?1 s^?1 after thermal annealing. Molecules TADPP3 and TADPP2‐TT were utilized as p‐type photovoltaic materials to fabricate organic solar cells after blending with phenyl C₇₁ butyric acid methyl ester ( PC₇₁BM ) and phenyl C₆₁ butyric acid methyl ester ( PC₆₁BM ). The relatively low J_SC and fill factor values can be attributed to poor film morphologies based on AFM and XRD studies. A solar cell with a thin film of TADPP3 with PC₇₁BM in a weight ratio of 1:2 exhibits a high open‐circuit voltage (V_OC) of 0.99 V and a power conversion efficiency (PCE) of 2.47 %. Interestingly, TADPP3 can also be employed as an n‐type photovoltaic material. The blended thin film of TADPP3 with P3HT in a weight ratio of 1:2 gave a high V_OC of 1.11 V and a PCE of 1.08 % after thermal annealing.     

Effect of side‐chain positions on morphology and photovoltaic properties of phenazine‐based donor–acceptor copolymers

Two phenazine donor–acceptor‐conjugated copolymers (P1 and P2) with the same polymer backbone but different anchoring positions of alkoxy chain on the phenazine unit were investigated to identify the effect of changing the position of alkoxy chains on their optical, electrochemical, blend film morphology, and photovoltaic properties. Although the optical absorption and frontier orbital energy levels were insensitive to the position of alkoxy chains, the film morphologies and photovoltaic performances changed significantly. P1/PC₇₁BM blend film showed the formation of phase separation with large coarse aggregates, whereas P2/PC₇₁BM blend film was homogeneous and smooth. Accordingly, power conversion efficiency (PCE) of photovoltaic devices increased from 1.50% for P1 to 2.54% for P2. In addition, the PCE of the polymer solar cell based on P2/PC₇₁BM blend film could be further improved to 3.49% by using solvent vapor annealing treatment. These results clearly revealed that tuning the side‐chain position could be an effective way to adjust the morphology of the active layer and the efficiency of the photovoltaic device. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2910–2918     

Coating on a Cold Substrate Largely Enhances Power Conversion Efficiency of the Bulk Heterojunction Solar Cell

Spin‐coating a mixture solution of P3HT and PCBM on a cold substrate largely enhanced the power conversion efficiency (PCE) of the bulk heterojunction (BHJ) solar cells. This concept was based on the abrupt decrease in the solubility of P3HT as solution temperature decreased. The selective precipitation of P3HT on the PEDOT:PSS‐coated cold substrate facilitated a desirable rich composition of P3HT at the interface with the PEDOT:PSS layer. The high crystallinity of P3HT suppressed the movement of PCBM during thermal annealing, preventing aggregation of PCBM. The morphological excellence of the pristine film gave a comparable PCE to that made by the conventional fabrication process. After thermal annealing, the device made via coating on a cold substrate showed above 30% increase in PCE from the BHJ solar cells made by the conventional method.

     

Effect of additives on the photovoltaic properties of organic solar cells based on triphenylamine-containing amorphous molecules

Photovoltaic performance of the organic solar cells(OSCs)based on 2-((5′-(4-((4-((E)-2-(5′-(2,2-dicyanovinyl)-3′,4-dihexyl-2,2′-bithiophen-5-yl)vinyl)phenyl)(phenyl)amino)styryl)-4,4′-dihexyl-2,2′-bithiophen-5-yl)methylene)malononitrile(L(TPAbTV-DCN))as donor and PC70BM as acceptor was optimized using 0.25 vol%high boiling point solvent additive of1-chloronaphthalene(CN),1,6-hexanedithiol(HDT),or 1,8-diodooctane(DIO).The optimized OSC based on L(TPA-bTVDCN)–PC70BM(1:2,w/w)with 0.25 vol%CN exhibits an enhanced power conversion efficiency(PCE)of 2.61%,with Voc of0.87 V,Jsc of 6.95 mA/cm2,and FF of 43.2%,under the illumination of 100 mW/cm2 AM 1.5 G simulated solar light,whereas the PCE of the OSC based on the same active layer without additive is only 1.79%.The effect of the additive on absorption spectra and the atomic force microscopy images of L(TPA-bTV-DCN)–PC70BM blend films were further investigated.The improved efficiency of the device could be ascribed to the enhanced absorption and optimized domain size in the L(TPA-bTV-DCN)–PC70BM blend film.     

Effects of spin-coating speed on the morphology and photovoltaic performance of the diketopyrrolopyrrole-based terpolymer

Polymer solar cells（PSCs） were fabricated by combining a diketopyrrolopyrrole-based terpolymer（PTBT-HTID-DPP） as the electron donor, and [6,6]-phenyl C₆₁ butyric acid methyl ester(PC₆₁BM) as the electron acceptor, and the power conversion efficiency（PCE） of 4.31% has been achieved under AM 1.5 G(100 m W cm^-2) illumination condition via optimizing the polymer/PC₆₁BM ratio, the variety of solvent and the spin-coating speed. The impact of the spin-coating speed on the photovoltaic performance of the PSCs has been investigated by revealing the effects of the spin-coating speed on the morphology and the absorption spectra of the polymer/PC₆₁BM blend films. When the thickness of the blend films are adjusted by spin-coating a fixed concentration with different spin-coating speeds, the blend film prepared at a lower spin-coating speed shows a stronger absorption per unit thickness, and the correspond device shows higher IPCE value in the longer-wavelength region. Under the conditions of similar thickness, the blend film prepared at a lower spin-coating speed forms a more uniform microphase separation and smaller domain size which leads to a higher absorption intensity per unit thickness of the blend film in long wavenumber band, a larger short-circuit current density(J_sc) and a higher power conversion efficiency（PCE） of the PSC device. Noteworthily, it was found that spin-coating speed is not only a way to control the thickness of active layer but also an influencing factor on morphology and photovoltaic performance for the diketopyrrolopyrrole-based terpolymer.     

Efficient ternary blend bulk heterojunction solar cells with tunable open-circuit voltage

To explore the potential of ternary blend bulk heterojunction (BHJ) photovoltaics as a general platform for increasing the attainable performance of organic solar cells, a model system based on poly(3-hexylthiophene) (P3HT) as the donor and two soluble fullerene acceptors, phenyl-C(61)-butyric acid methyl ester (PC(61)BM) and indene-C(60) bisadduct (ICBA), was examined. In all of the solar cells, the overall ratio of polymer to fullerene was maintained at 1:1, while the composition of the fullerene component (PC(61)BM:ICBA ratio) was varied. Photovoltaic devices showed high short-circuit current densities (J(sc)) and fill factors (FF) (>0.57) at all fullerene ratios, while the open-circuit voltage (V(oc)) was found to vary from 0.61 to 0.84 V as the fraction of ICBA was increased. These results indicate that the V(oc) in ternary blend BHJ solar cells is not limited to the smallest V(oc) of the corresponding binary blend solar cells but can be varied between the extreme V(oc) values without significant effect on the J(sc) or FF. By extension, this result suggests that ternary blends provide a potentially effective route toward maximizing the attainable J(sc)V(oc) product (which is directly proportional to the solar cell efficiency) in BHJ solar cells and that with judicious selection of donor and acceptor components, solar cells with efficiencies exceeding the theoretical limits for binary blend solar cells could be possible without sacrificing the simplicity of a single active-layer processing step.     

Synthesis, characterization and photovoltaic properties of a low-bandgap platinum(II) polyyne functionalized with a 3,4-ethylenedioxythiophene-benzothiadiazole hybrid spacer

The synthesis, characterization and optical spectroscopy of a deep blue platinum(II) polyyne functionalized with the (3,4-ethylenedioxythiophene)-benzothiadiazole hybrid spacer (P1) and its dinuclear platinum molecular model complex (M1) are described. This metalated polymer P1 exhibits good thermal stability and possesses a narrow bandgap of 1.76 eV. Optical spectroscopic measurements of these materials reveal a substantial donor-acceptor interaction along the rigid backbone of the organometallic polyynes through the interaction of metal center and the conjugated tricyclic ligand. Preliminary study shows that P1: methanofullerene acceptor blend can be used as an active layer of bulk-heterojunction polymer solar cells. Photoexcitation of this blend layer in some yet-to-be optimized cells results in a photo-induced electron transfer from the π-conjugated metallopolyyne electron donor to [6,6]-phenyl C₆₁-butyric acid methyl ester with a power conversion efficiency (PCE) close to 0.30% under air mass (AM1.5) simulated solar illumination. The power dependencies of the solar cell parameters (including the short-circuit current density, open-circuit voltage, fill-factor and PCE) were also studied.     

An acrylated fullerene derivative for efficient and thermally stable polymer solar cells

The continuous microstructure evolution occurring in active layers of polymer-fullerene solar cells is one of the main causes for their device instability. With aim to tackle it, this work developed a new polymerizable fullerene acceptor, [6,6]-phenyl-C₆₁-butyl acrylate (PC₆₁BA). It was found that PC₆₁BA has similar light-absorption properties and HOMO and LUMO energy levels as [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM), and can be converted into insoluble oligomers upon heating at 150 °C. Polymer-fullerene solar cells using poly(3-hexylthiophene) (P3HT) as donor and PC₆₁BA as acceptor exhibited an optimized efficiency of 3.54%, the performance comparable to P3HT/PC₆₁BM cells (optimized efficiency: 3.70%). But, the former possess much better thermal stability than the latter owing to aggregation suppression by the polymerized PC₆₁BA. These results indicate that PC₆₁BA, unlike most previous reported, is a unique polymerizable fullerene derivative that can be used alone as acceptor to achieve both efficient and thermally stable polymer solar cells.