聚3-己基噻吩：非富勒烯太阳能电池中的量子效率损失和电压损失

From the industrial perspective, poly(3-hexylthiophene) (P3HT) is one of the most attractive donor materials in organic photovoltaics. The large bandgap in P3HT makes it particularly promising for efficient indoor light harvesting, a unique advantage of organic photovoltaic (PV) devices, and this has started to gain considerable attention in the field of PV technology. In addition, the up-scalability and long material stability associated with the simple chemical structure make P3HT one of the most promising materials for the mass production of organic solar cells. However, the solar cells based on P3HT has a low power conversion efficiency (PCE), which is less than 11%, mainly due to significant voltage losses. In this study, we identified the origin of the high quantum efficiency and voltage losses in the P3HT: non-fullerene based solar cells, and we proposed a strategy to reduce the losses. More specifically, we observed that: 1) the non-radiative decay rate of the charge transfer (CT) states formed at the donor–acceptor interfaces was much higher for the P3HT: non-fullerene solar cells than that for the P3HT: fullerene solar cells, which was the main reason for the more severely limited photovoltage; 2) the origin of the high non-radiative decay rate in the P3HT: non-fullerene solar cell could be ascribed to the short packing distance between the P3HT and non-fullerene acceptor molecules at the donor–acceptor interfaces (DA distance), which is a rarely studied interfacial structural property, highly important in determining the decay rate of CT states; 3) the lower voltage loss in the state-of-the-art P3HT solar cell based on the 2, 2'-((12, 13-bis(2-butyldecyl)-3, 9-diundecyl-12, 13-dihydro-[1, 2, 5]-thiadiazolo[3, 4-e]thieno[2', 3': 4', 5']thieno[2', 3': 4, 5]p-yrolo[3, 2-g]thieno[2', 3': 4, 5]thieno[3, 2-b]indole-2, 10-diyl)bis(methanelylidene))bis(5, 6-dichloro-1H-indene-1, 3(2H)-dion-e) (ZY-4Cl) acceptor could be associated with the better alignment of the energy levels of the active materials and the longer DA distance, compared to those based on the commonly used acceptors. However, the DA distance was still very short, limiting the device voltage. Thus, improving the performance of the P3HT based solar cells requires a further increase in the DA distance. Our findings are expected to pave the way for breaking the performance bottleneck of the P3HT based solar cells.     

聚3-己基噻吩：非富勒烯太阳能电池中的量子效率损失和电压损失

聚3-己基噻吩(P3HT)以其合成工艺简单、成本低廉的优势,成为有机光伏领域中最具吸引力的电子给体材料之一。然而,目前P3HT: 非富勒烯太阳能电池的光伏性能仍然较差。在本工作中,我们证明了与P3HT: 富勒烯太阳能电池相比,较快的电荷转移态的非辐射衰减速率(K_nr)是导致P3HT: 非富勒烯太阳能电池中较低的量子效率和较高的电压损失的原因。然后,我们研究了基于非富勒烯受体ZY-4Cl的太阳能电池的工作机理。研究结果表明与P3HT: 非富勒烯体系相比,P3HT: ZY-4Cl中K_nr的降低改善了器件的量子效率,同时降低了电压损失。K_nr降低的原因可以部分归因于电荷转移态能量的增加。此外,给体分子和受体分子之间的距离(DA间距)的增大也是K_nr减少的重要原因。因此,我们得出结论：为了提高P3HT太阳能电池的性能,需进一步降低器件的K_nr,这可通过增加活性层中的DA间距来实现。     

Tuning the Dimensions of ZnO Nanorod Arrays for Application in Hybrid Photovoltaics

ZnO nanorod arrays are a very eligible option as electron acceptor material in hybrid solar cells, owing to their favorable electrical properties and abundance of available, easy, and low‐cost synthesis methods. To become truly effective in this field, a major prerequisite is the ability to tune the nanorod dimensions towards optimal compatibility with electron‐donating absorber materials. In this work, a water‐based seeding and growth procedure is used to synthesize ZnO nanorods. The nanorod diameter is tuned either by modifying the zinc concentration of the seeding solution or by changing the concentration of the hydrothermal growth solution. The consequences of this morphological tailoring in the performance of hybrid solar cells are investigated, which leads to a new record efficiency of 0.82 % for hydrothermally grown ZnO nanorods of size 300 nm in combination with poly(3‐hexylthiophene‐2,5‐diyl) (P3HT). This improvement is attributed to a combined effect of nanorod diameter and orientation, and possibly to a better alignment of the P3HT backbone resulting in improved charge transport.     

Large open-circuit voltage polymer solar cells by poly(3-hexylthiophene) with multi-adducts fullerenes

Polymer solar cells (PSCs) made by poly(3-hexylthiophene) (P3HT) with multi-adducts fullerenes, [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM), PC61BM-bisadduct (bisPC61BM) and PC61BM-trisadduct (trisPC61BM), were reported. Electrochemistry studies indicated that PC61BM, bisPC61BM and trisPC61BM had step-up distributional lowest unoccupied molecular orbital (LUMO) energy. PSCs made by P3HT with above PC61BMs show a trend of enlarged open-circuit voltages, which is in good agreement with the energy difference between the LUMO of PC61BMs and the HOMO of P3HT. On the contrary, reduced short-circuit currents (Jsc) were observed. The investigation of photo responsibility, dynamics analysis based on photo-induced absorption of composite films, P3HT:PC61BMs and n-channel thin film field-effect transistors of PC61BMs suggested that the short polaron lifetimes and low carrier mobilities were response for reduced Jsc. All these results demonstrated that it was important to develop an electron acceptor which has both high carrier mobility, and good compatibility with the electron donor conjugated polymer for approaching high performance PSCs.     

Correlating interface heterostructure, charge recombination, and device efficiency of poly(3-hexyl thiophene)/TiO2 nanorod solar cell

The charge recombination rate in poly(3-hexyl thiophene)/TiO(2) nanorod solar cells is demonstrated to correlate to the morphology of the bulk heterojunction (BHJ) and the interfacial properties between poly(3-hexyl thiophene) (P3HT) and TiO(2). The recombination resistance is obtained in P3HT/TiO(2) nanorod devices by impedance spectroscopy. Surface morphology and phase separation of the bulk heterojunction are characterized by atomic force microscopy (AFM). The surface charge of bulk heterojunction is investigated by Kelvin probe force microscopy (KPFM). Lower charge recombination rate and lifetime have been observed for the charge carriers in appropriate heterostructures of hybrid P3HT/TiO(2) nanorod processed via high boiling point solvent and made of high molecular weight P3HT. Additionally, through surface modification on TiO(2) nan,orod, decreased recombination rate and longer charge carrier lifetime are obtained owing to creation of a barrier between the donor phases (P3HT) and the acceptor phases (TiO(2)). The effect of the film morphology of hybrid and interfacial properties on charge carrier recombination finally leads to different outcome of photovoltaic I-V characteristics. The BHJ fabricated from dye-modified TiO(2) blended with P3HT exhibits 2.6 times increase in power conversion efficiency due to the decrease of recombination rate by almost 2 orders of magnitude as compared with the BHJ made with unmodified TiO(2). In addition, the interface heterostructure, charge lifetime, and device efficiency of P3HT/TiO(2) nanorod solar cells are correlated.     

Role of structural order and excess energy on ultrafast free charge generation in hybrid polythiophene/Si photovoltaics probed in real time by near-infrared broadband transient absorption

Despite the central role of light absorption and the subsequent generation of free charge carriers in organic and hybrid organic-inorganic photovoltaics, the precise process of this initial photoconversion is still debated. We employ a novel broadband (UV-Vis-NIR) transient absorption spectroscopy setup to probe charge generation and recombination in the thin films of the recently suggested hybrid material combination poly(3-hexylthiophene)/silicon (P3HT/Si) with 40 fs time resolution. Our approach allows for monitoring the time evolution of the relevant transient species under various excitation intensities and excitation wavelengths. Both in regioregular (RR) and regiorandom (RRa) P3HT, we observe an instant (<40 fs) creation of singlet excitons, which subsequently dissociate to form polarons in 140 fs. The quantum yield of polaron formation through dissociation of delocalized excitons is significantly enhanced by adding Si as an electron acceptor, revealing ultrafast electron transfer from P3HT to Si. P3HT/Si films with aggregated RR-P3HT are found to provide free charge carriers in planar as well as in bulk heterojunctions, and losses are due to nongeminate recombination. In contrast for RRa-P3HT/Si, geminate recombination of bound carriers is observed as the dominant loss mechanism. Site-selective excitation by variation of pump wavelength uncovers an energy transfer from P3HT coils to aggregates with a 1/e transfer time of 3 ps and reveals a factor of 2 more efficient polaron formation using aggregated RR-P3HT compared to disordered RRa-P3HT. Therefore, we find that polymer structural order rather than excess energy is the key criterion for free charge generation in hybrid P3HT/Si solar cells.     

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.     

基于富勒烯和噻吩聚合物的本体异质结太阳电池

随着全球能源需求量的逐年增加,对可再生能源的有效利用成为亟待解决的问题。现在使用的能源多来自矿物燃料的开采,其中包括石油、天然气和煤等,而这些资源是非常有限的。因此,发展新能源和新能源材料是我国进入21世纪必须解决的重大课题,其中太阳能被认为是清洁可再生新能源的代表之一。基于噻吩跟富勒烯的异质结太阳能电池是目前太阳能电池的重要发展方向之一。该种太阳能电池因其制备简单、成本低廉、重量轻和可制成柔性器件等优点近年来受到多方的广泛重视。经过努力,该种太阳能电池的光电转化性能已经得到了一定提高,最高光电转化效率已达到7%左右,但是跟无机半导体硅和染料敏化太阳能电池相比还有一定差距。因此,这方面的研究任重而道远,研究空间也非常大。本文从材料合成的角度,简要综述了近年来国内外在基于富勒烯和噻吩的异质结太阳能电池方面所取得的最新研究进展,并对下一步需要研究的热点问题作了展望。     

Triplet exciton generation in bulk-heterojunction solar cells based on endohedral fullerenes

Organic bulk-heterojunctions (BHJ) and solar cells containing the trimetallic nitride endohedral fullerene 1-[3-(2-ethyl)hexoxy carbonyl]propyl-1-phenyl-Lu(3)N@C(80) (Lu(3)N@C(80)-PCBEH) show an open circuit voltage (V(OC)) 0.3 V higher than similar devices with [6,6]-phenyl-C[61]-butyric acid methyl ester (PC(61)BM). To fully exploit the potential of this acceptor molecule with respect to the power conversion efficiency (PCE) of solar cells, the short circuit current (J(SC)) should be improved to become competitive with the state of the art solar cells. Here, we address factors influencing the J(SC) in blends containing the high voltage absorber Lu(3)N@C(80)-PCBEH in view of both photogeneration but also transport and extraction of charge carriers. We apply optical, charge carrier extraction, morphology, and spin-sensitive techniques. In blends containing Lu(3)N@C(80)-PCBEH, we found 2 times weaker photoluminescence quenching, remainders of interchain excitons, and, most remarkably, triplet excitons formed on the polymer chain, which were absent in the reference P3HT:PC(61)BM blends. We show that electron back transfer to the triplet state along with the lower exciton dissociation yield due to intramolecular charge transfer in Lu(3)N@C(80)-PCBEH are responsible for the reduced photocurrent.     

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.     

Combined parametric optimization of P3HT: PC70BM films for efficient bulk-heterojunction solar cells

Journal of Solid State Electrochemistry - In this report, the effects of photoactive blend compositions, film thicknesses, and annealing conditions on the P3HT:PC70BM solar cells performance and...     

聚方酸太阳电池材料的合成与表征

通过Yamamoto偶联反应,合成了主链含有1,2-取代方酸和1,3-取代方酸结构单元的新型共轭聚合物光伏材料PTST.其结构经过红外光谱和核磁共振表征得以确证.热分析、紫外-可见吸收光谱和电化学性质研究表明,所得新型共轭聚合物PTST具有良好的热稳定性;在270～700 nm光谱范围内有宽而强的吸收,基本覆盖了整个可见光区域;取代方酸结构单元的引入可使聚合物的最低未占有轨道(LUMO)和能隙(Eg)降低.当PTST仅为60%掺混时,即可使聚(3-己基噻吩)的荧光完全淬灭,说明P3HT与PTST之间存在明显的光电子转移.     

Effect of 1,8-Diiodooctane Content on the Performance of P3HT:PC61BM Bulk Heterojunction Photodetectors

A series of polymer photodetectors with device configuration of ITO/PEDOT:PSS/P_3 HT:PC_(61) BM/C_(60)/Al were prepared by using P_3 HT as the donor material and PC_(61) BM as the acceptor material. By regulating the content of 1,8-diiodooctane(DIO)(V/V: 1%, 3%, 5%) as a processing additive, the morphology of the active layer can be greatly improved. With C_(60) as the hole blocking layer, the dark current density of the device can be reduced by about an order of magnitude. When employing 3% DIO(V/V) in the active layer processing, the photodetetcors present the best performance, and the detectivity of the device is 1.52×10~(12) Jones at 540 nm under a bias of-0.1 V. Moreover, it also has a wider linear dynamic range of 60 dB as well as faster response speed(τ_r/τ_f=0.53/0.71 μs) than those of devices with other content of DIO additives.     

光敏层厚度与退火温度调控对聚3-己基噻吩光电探测器性能的影响

以聚3-己基噻吩(P3HT)为给体材料,富勒烯衍生物(PC61BM)为受体材料,制备了一系列结构为ITO/PEDOT:PSS/P3HT:PC61BM/C60/Al的体异质结光电探测器.研究了120、160、180与200 nm不同光敏层厚度,100、120、130、140与150℃不同退火温度等条件对器件性能的影响,并采用原子力显微镜(AFM)对光敏层形貌进行了分析.研究发现,基于180 nm厚光敏层、150℃退火处理的器件,在-2 V的偏压下550 nm处有最大响应度,为268 mA/W,并且在470~610 nm范围内响应度都超过了200 mA/W;基于180 nm厚光敏层、120℃退火处理的器件有最大线性动态范围,为95 dB.研究表明,适当厚度的光敏层有利于提高光吸收效率与器件的光伏性能;退火处理,可以使光敏层形成均匀的互穿网络结构,进而减小空穴与电子的复合概率,提高器件的光伏性能.     

Effect of morphology on ultrafast free carrier generation in polythiophene:fullerene organic solar cells

Despite significant study, the precise mechanisms that dictate the efficiency of organic photovoltaic cells, such as charge separation and recombination, are still debated. Here, we directly observe efficient ultrafast free charge generation in the absence of field in annealed poly(3-hexylthiophene):methanofullerene (P3HT:PCBM). However, we find this process is much less efficient in unannealed and amorphous regiorandom blends, explaining the superior short-circuit current and fill-factor of annealed RR-P3HT:PCBM solar cells. We use transient optical spectroscopy in the visible and near-infrared spectral region covering, but not limited to, the previously unobserved and highly relevant time scale spanning 1 to 100 ns, to directly observe both geminate and nongeminate charge recombination. We find that exciton quenching leads directly (time scale less than 100 fs) to two populations: bound charges and free charges. The former do not lead to photocurrent in a photovoltaic cell; they recombine geminately within 2 ns and are a loss channel. However, the latter can be efficiently extracted in photovoltaic cells. Therefore, we find that the probability of ultrafast free charge formation after exciton quenching directly limits solar cell efficiency. This probability is low in disordered P3HT:PCBM blends but approaches unity in annealed blends.     

Electronic Structure Effect of Polythiophene Derivatives and Nano N-Zn-Ag/TiO2 on Performance of Organic Thin Film Solar Cell

Nanocrystal N-Zn-Ag/TiO₂ powders were prepared with N-Zn/TiO₂ by photo deposition method. A series of pure polymers P3HT[poly(3-hexylthiophene)], P3OT[poly(3-octylthiophene)], P3DT[poly(3-decylthiophene)] and P3DDT[poly(3-dodecylthiophene)], was synthesized, which were used to synthesize p-n type semiconductor materials P3HT/N-Zn-Ag-TiO₂, P3OT/N-Zn-Ag-TiO₂, P3DT/N-Zn-Ag-TiO₂ and P3DDT/N-Zn-Ag-TiO₂ by in situ che-mical method. X-Ray diffraction(XRD) and infrared(IR) spectroscopy showed the structure of the polymers and complexes. Ultraviolet-visible(UV-Vis) spectra and cyclic voltammograms(CV) showed the optical and electronic performance of the polymers and complexes. Two new single and double organic thin film heterojunction solar cells were prepared with the above mentioned synthesized powders as raw materials. Current-voltage(I-V) measurements indicate that the conversion efficiency of the single organic thin film heterojunction solar cell is higher than that of the double organic thin film heterojunction solar cells. Single organic thin film heterojunction solar cells based on P3DT/N-Zn-Ag-TiO₂ can get a photoelectric conversion efficiency of 0.0408%. The performance of electronic transform between electron donor and acceptor on organic thin film solar cells was researched.     

Stable and Low‐Cost Mesoscopic CH3NH3PbI2Br Perovskite Solar Cells by using a Thin Poly(3‐hexylthiophene) Layer as a Hole Transporter

Mesoscopic perovskite solar cells using stable CH₃NH₃PbI₂Br as a light absorber and low‐cost poly(3‐hexylthiophene) (P3HT) as hole‐transporting layer were fabricated, and a power conversion efficiency of 6.64 % was achieved. The partial substitution of iodine with bromine in the perovskite led to remarkably prolonged charge carrier lifetime. Meanwhile, the replacement of conventional thick spiro‐MeOTAD layer with a thin P3HT layer has significantly reduced the fabrication cost. The solar cells retained their photovoltaic performance well when they were exposed to air without any encapsulation, presenting a favorable stability. The combination of CH₃NH₃PbI₂Br and P3HT may render a practical and cost‐effective solid‐state photovoltaic system. The superior stability of CH₃NH₃PbI₂Br is also promising for other photoconversion applications.     

Optoelectronic Properties of Dicyanofluorene‐Based n‐Type Polymers

Three new donor–acceptor‐type copolymers ( P1 , P2 , P3 ) consisting of dicyanofluorene as acceptor and various donor moieties were designed and synthesized. Optoelectronic properties were studied in detail by means of UV‐visible absorption and fluorescence spectroscopy, cyclic voltammetry, space‐charge‐limited current (SCLC), flash‐photolysis time‐resolved microwave conductivity (FP‐TRMC), and density functional theory (DFT). All polymers showed strong absorption in the UV‐visible region and the absorption maximum undergoes redshift with an increasing number of thiophene units in the polymer backbone. SCLC analysis showed that the electron mobilities of the polymers in the bulk state were 1 to 2 orders higher than that of the corresponding hole mobilities, which indicated the n‐type nature of the materials. By using FP‐TRMC, the intrapolymer charge‐carrier mobility was assessed and compared with the interpolymer mobility obtained by SCLC. The polymers exhibited good electron‐accepting properties sufficiently high enough to oxidize the excited states of regioregular poly(3‐hexylthiophene) (P3HT (donor)), as evident from the FP‐TRMC analysis. The P3 polymer exhibited the highest FP‐TRMC transients in the pristine form as well as when blended with P3HT. Use of these polymers as n‐type materials in all‐polymer organic solar cells was also explored in combination with P3HT. In accordance with the TRMC results, P3 exhibited superior electron‐transport and photovoltaic properties to the other two polymers, which is explained by the distribution of the energy levels of the polymers by using DFT calculations.     

P3HT修饰一维有序壳核式CdS/ZnO纳米棒阵列复合膜的光电化学性能

采用电化学方法在铟锡氧化物(ITO)导电玻璃上制备了高度有序的ZnO纳米棒阵列, 在ZnO纳米棒阵列上先后电化学沉积CdS纳米晶膜及聚3-己基噻吩(P3HT)薄膜得到P3HT修饰的一维有序壳核式CdS/ZnO纳米阵列结构, 并通过扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、能量散射X射线(EDX)等表征手段证实了该结构的形成. 以此纳米结构薄膜为光阳极组装新型半导体敏化太阳电池, 研究了CdS纳米晶膜的厚度和P3HT薄膜的沉积对电池光伏性能的影响, 初步探讨了电荷在电池结构中的传输机理, 结果表明, CdS纳米晶膜和P3HT薄膜的沉积有效地拓宽了光阳极的光吸收范围, 实验中电池的光电转换效率最高达到1.08%.     

Impact of Alkoxyl Tail of Fullerene Dyad Acceptor on Crystalline Microstructure for Efficient External Treatment-free Polymer Solar Cells with Poly(3-hexylthiophene) as Donor

A series of tri(alkoxyl)benzene-fullerene dyads(PCBB-Cn, n=4, 6, 8, 10, 12) with varied tri(alkoxyl) chain lengths was designed, synthesized and used as acceptor materials in polymer solar cells(PSCs). The five fullerene dyads possess similar absorption spectra in dilute solution, decreased glass-transition temperature(T_g) and gradually elevated lowest unoccupied molecular orbital(LUMO) energy levels from -3.87 eV to -3.73 eV with the increase of the alkoxy chain length. In the fabrication of PSCs with poly(3-hexylthiophene)(P3HT) as donor and the fullerene dyads as acceptor, PCBB-Cn with longer tri(alkoxyl) chains and lower T_g can induce crystalline structure of P3HT during spin-coating the photoactive layer at room temperature and form nanoscale phase separated interpenetrating network of P3HT:PCBB-Cn blend films, which results in the improvement of photovoltaic performance of PSCs. A power conversion efficiency of 3.03% for the PSCs based on P3HT:PCBB-C10 was obtained without thermal annealing or solvent annealing. The thermal and solvent annealing-free fabrication using the fullerene dyads as acceptor is very important for the roll to roll production of PSCs with flexible large area.