Increased open‐circuit voltage of ZnO nanowire/PbS quantum dot bulk heterojunction solar cells with solution‐deposited Mg(OH)2 interlayer

An ultrathin Mg(OH)₂ layer was solution‐deposited onto the ZnO nanowires to solve the problem of interfacial charge recombination, caused by the increase of interfacial area in bulk heterojunction (BHJ) PbS colloidal quantum dot solar cells (CQDSCs). This Mg(OH)₂ interlayer efficiently passivated the surface defects of ZnO nanowires and provided tunnel barrier at ZnO/PbS interface. As a result, the charge recombination at ZnO/PbS interface was largely suppressed, proved by the significantly elongated electron lifetime and the increased open‐circuit voltage of the Mg(OH)₂‐involved BHJ CQDSCs. Careful thickness optimization of Mg(OH)₂ interlayer finally brought a ～33% increase in V_oc and ～25% improvement in power conversion efficiency.     

Mg-doped ZnO layer to enhance electron transporting for PbS quantum dot solar cells

In this work, the effect of Mg doping on the performance of PbS quantum dot (QD) solar cells (QDSCs) is investigated. To elucidate that, PbS QDSCs with pristine ZnO and Mg-doped ZnO (ZMO) as electron transporting layers (ETLs) are fabricated, respectively. The current density-voltage (J-V) measurements are performed. The results show that the cell efficiency of the device with ZMO as an ETL is 9.46%, which increases about 75% compared to that of the pristine ZnO based device (5.41%). Enhanced short current density (J_sc) and fill factor (FF) are observed. It is demonstrated that Mg doping could passivate the surface defects and suppress the carrier recombination in ZnO ETL, thus resulting in larger bandgap and higher Fermi level (E_F). The strategy of Mg-doped ZnO ETL provides a promising way for pushing solar cell performance to a high level.     

PbS colloidal quantum dot/ZnO‐based bulk‐heterojunction solar cells with high stability under continuous light soaking

PbS colloidal quantum dot (CQD)‐based depleted bulk‐heterojunction solar cells were constructed, using the 1.2 μm thick nanowire array infiltrated with PbS QDs bearing Br ligands. The long‐term stability tests were performed on the solar cells without encapsulation in air under continuous light soaking using a Xe lamp with an AM1.5G filter (100 mW cm^?2). Time course of solar cell performances during the tests showed two time periods with distinct behavior, that is, the initial transient time period and the relatively stable region following it. The power conversion efficiency was found to keep approximately 90% of the initial value at the end of the 3000 h light soaking test. The stability tests suggest that the PbS surface modification or passivation reactions play an important role in achieving such a high stability, and demonstrate that PbS CQD/ZnO nanowire array‐based depleted bulk‐heterojunction solar cells are highly stable. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Effect of CdS modification on photoelectric properties of TiO2/PbS quantum dots bulk heterojunction

TiO₂/PbS(CdS) quantum dots (QDs) bulk heterojunction has been fabricated by successive ionic layer adsorption and reaction method via alternate deposition of PbS and CdS QDs. In comparison with TiO₂/PbS heterojunction, the incident photon to current conversion efficiency was increased almost 50% in the visible region. Meantime, the short-circuit current and open-circuit voltage were enhanced 200% and 35% respectively. The influence mechanism of CdS is related to reduction of trap state density at TiO₂/PbS interface and PbS QDs surface by the discussion of the dark current density–voltage curves, the transient photocurrent response curves and the electrochemical impedance spectra spectroscopy (EIS).     

Cu_2O/ZnO氧化物异质结太阳电池的研究进展

介绍了近年来低成本Cu_2O/ZnO氧化物异质结太阳电池方面的研究进展.应用于光伏器件的吸收层材料Cu_2O是直接带隙半导体材料,天然呈现p型;其原材料丰富,且对环境友好.Cu_2O/ZnO异质结太阳电池结构主要有平面结构和纳米线/纳米棒结构.纳米结构的Cu_2O太阳电池提高了器件的电荷收集作用;通过热氧化Cu片技术获得的具有大晶粒尺寸平面结构Cu_2O吸收层在Cu_2O/ZnO太阳电池应用中展现出了高质量特性.界面缓冲层(如i-ZnO,a-ZTO,Ga_2O_3等)和背表面电场(如p~+-Cu_2O层等)可有效地提高界面处能级匹配和增强载流子输运.10 nm厚度的Ga_2O_3提供了近理想的导带失配,减少了界面复合;Ga_2O_3非常适合作为界面层,其能够有效地提高Cu_2O基太阳电池的开路电压V_(oc)(可达到1.2 V)和光电转换效率.p~+-Cu_2O(如Cu_2O:N和Cu_2O:Na)能够减少器件中背接触电阻和形成电子反射的背表面电场(抑制电子在界面处复合).利用p型Na掺杂Cu_2O(Cu_2O:Na)作为吸收层和Zn_(1-x)Ge_x-O作为n型缓冲层,Cu_2O异质结太阳电池(器件结构:MgF_2/ZnO:Al/Zn_(0.38)Ge_(0.62)-O/Cu_2O:Na)光电转换效率达8.1%.氧化物异质结太阳电池在光伏领域展现出极大的发展潜力.     

Effect of an Al-doped ZnO electron transport layer on the efficiency of inverted bulk heterojunction solar cells

Doping is a widely-implemented strategy for enhancing the inherent electrical properties of metal oxide charge transport layers in photovoltaic devices because higher conductivity of electron transport layer (ETL) can increment the photocurrent by reducing the series resistance. To improve the conductivity of ETL, in this study we doped the ZnO layer with aluminum (Al), then investigated the influence of AZO on the performance of inverted bulk heterojunction (BHJ) polymer solar cells based on poly [[4,8-bis [(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b’]dithiophene-2,6-diyl]-[3-fluoro-2[(2-ethylhexyl)-carbonyl]-thieno-[3,4-b]thiophenediyl ]] (PTB7):[6,6]-phenyl C71 butyric acid methyl ester (PC₇₁BM). The measured conductivity of AZO was ~10⁻³ S/cm, which was two orders of magnitude higher than that of intrinsic ZnO (~10⁻⁵ S/cm). By decreasing the series resistance (R_s) in a device with an AZO layer, the short circuit current (J_sc) increased significantly from 15.663 mA/cm² to 17.040 mA/cm². As a result, the device with AZO exhibited an enhanced power conversion efficiency (PCE) of 8.984%.     

Fabrication and characterization of fullerene/porphyrin bulk heterojunction solar cells

Fullerene/porphyrin bulk heterojunction solar cells were fabricated and, the electronic and optical properties were investigated. Effects of exciton-diffusion blocking layer of perylene derivative on the solar cells between active layer and metal layer were also investigated. Optimized structures with the exciton-diffusion blocking layer improved conversion efficiencies. Energy levels of the molecules were calculated and discussed. Nanostructures of the solar cells were investigated by X-ray and electron diffraction, which indicated formation of fullerene/porphyrin mixed crystals. Electronic structures of the molecules were investigated by molecular orbital calculation, and energy levels of the solar cells were discussed.     

Raman study of InAs/GaAs quantum dot solar cells

We report polarized and resonant Raman study of InAs/GaAs quantum dot solar cell (QDSC) structures. Raman spectra obtained from the top surfaces of the samples suggested that the formation of InAs QDs induced tensile strain in the overgrown GaAs layers. Furthermore, a longitudinal optical phonon-plasmon (LPP) coupled modes were observed in the p-type GaAs layers. The tensile strain was increased with an increase in the QD size. The hole concentrations estimated by fitting the individual LPP coupled modes were in the range of 2.4–3.5 × 10¹⁸ cm^?3. Resonant Raman spectra obtained from the cleaved sides, where the QDs were located, showed a 225 cm^?1 mode in parallel polarization configurations. Based on accurate analysis, this mode was identified as the LA(X) phonon of GaAs.     

Performance and reliability improvement of La_2O_3/Al_2O_3 nanolaminates using ultraviolet ozone post treatment

La-based binary or ternary compounds have recently attracted a great deal of attention as a potential candidate to replace the currently used Hf-based dielectrics in future transistor and capacitor devices for sub-22 generation. However, the hygroscopic nature of La₂O₃ hampers its application as dielectrics in electron devices. To cope with this challenge, ultraviolet (UV) ozone post treatment is proposed to suppress the moisture absorption in the H₂O-based atomic layer deposition (ALD) La₂O₃/Al₂O₃ nanolaminates which is related to the residual hydroxyl/hydrogen groups after annealing. The x-ray photoelectron spectroscopy (XPS) and conductive atomic force microscopy (AFM) results indicate that the moisture absorption of the H₂O-based ALD La₂O₃/Al₂O₃ nanolaminates is efficiently suppressed after 600 ℃ annealing, and the electrical characteristics are greatly improved.     

Electron transport properties of TiO_2 shell on Al_2O_3 core in dye-sensitized solar cells

The performance of dye-sensitized solar cells(DSSCs)is strongly affected by the properties of semiconductor nanoparticles.In this work,we used TiO_2 particles prepared by TiCl_4 hydrolysis n times on Al_2O_3 films(A/T(n)),and investigated morphology,photoelectric,and electron transport properties of A/T(n).The TiO_2 shell was composed of 10-20 nm nanoparticles and the number of nanoparticles increased with increasing TiCl_4 treatment times.The highest photoelectric conversion efficiency of 3.23% was obtained as A/T(4).IMPS results indicated that electron transport rate was high enough to conduct current,and was not the dominating effect to limit the Jsc.Jsc was mainly determined by dye loading on TiO_2 and the interconnection of TiO_2.These may provide a new strategy for preparing semiconductor working electrodes for DSSC.     

Photoactive area modification in bulk heterojunction organic solar cells using optimization of electrochemically synthesized ZnO nanorods

In this work, Zn O nanorod arrays grown by an electrochemical deposition method are investigated. The crucial parameters of length, diameter, and density of the nanorods are optimized over the synthesize process and nanorods growth time. Crystalline structure, morphologies, and optical properties of Zn O nanorod arrays are studied by different techniques such as x-ray diffraction, scanning electron microscope, atomic force microscope, and UV–visible transmission spectra.The Zn O nanorod arrays are employed in an inverted bulk heterojunction organic solar cell of Poly(3-hexylthiophene):[6-6] Phenyl-(6) butyric acid methyl ester to introduce more surface contact between the electron transporter layer and the active layer. Our results show that the deposition time is a very important factor to achieve the aligned and uniform Zn O nanorods with suitable surface density which is required for effective infiltration of active area into the Zn O nanorod spacing and make a maximum interfacial surface contact for electron collection, as overgrowing causes nanorods to be too dense and thick and results in high resistance and lower visible light transmittance. By optimizing the thickness of the active layer on top of Zn O nanorods, an improved efficiency of 3.17% with a high FF beyond 60% was achieved.     

Hybrid bulk heterojunction solar cells based on blends of TiO2 nanorods and P3HT

Over the past decades, organic solar cells based on semiconducting polymers or small molecules have become a promising alternative to traditional inorganic photovoltaic devices. However, to address the intrinsic limitations of organic materials, such as charge separation yield, charge transport and durability, new strategies based on hybrid organic/inorganic materials have been explored. One such approach exploits mesoporous inorganic nanostructures as electron acceptors, which takes advantage of the potential to control the active layer structure and interface morphology through nanoparticle synthesis and processing. In this work, the potential of hybrid photovoltaics will be discussed and illustrated through a recent study of bulk heterojunction systems based on the blend of TiO₂ nanorods with a conjugated polymer. To cite this article: J. Bouclé et al., C. R. Physique 9 (2008).     

Single intermediate-band solar cells of InGaN/InN quantum dot supracrystals

We measured the elemental mappings in dental enamel of Gigantopithecus blacki (n=3) using synchrotron radiation X-ray fluorescence (SRXRF) to understand the dietary variation during the time of tooth eruption. In order to account for the effects of diagenesis on the variation of elements in these fossil teeth, we compared the Fe and Mn elemental distribution and levels in dental enamel of G. blacki with that of a single modern pig tooth and found no differences. The observation of the variations of Sr, Ca and RE (rare earth elements) distribution in the incremental lines reveals that the plant foods utilized by G. blacki from the early Pleistocene or the middle Pleistocene had varied during the formation of dental enamel, possibly caused by the change of living environment or food resources. The variations of elemental distribution in different incremental lines are very promising to understand the nutritional and physical stress of G. blacki during the tooth eruption and environmental adaptations.     

Influence of fullerene derivative replacement with TiO2 nanoparticles in organic bulk heterojunction solar cells

In an effort to develop hybrid organic solar cells with improved power conversion efficiency (PCE), devices based on poly (3-hexylthiophene) (P3HT):phenyl C₆₁-butyric acid methyl ester (PCBM) active layer and poly (3,4-ethylenedioxythiophene) (PEDOT):poly (styrenesulfonate) (PSS) buffer layers were prepared. A systematic replacement of PCBM was achieved by introducing nanostructured TiO₂ (∼15 nm particle size), dissolved separately in chlorobenzene (CB) and 1,2 –dichlorobenzene (DCB), to the (P3HT:PCBM) active layer while keeping a fixed amount for P3HT. To understand the effect of fullerene replacement with the inorganic metal oxide nanoparticles on different properties of resulting devices, a variety of techniques such as Current–Voltage (J–V) characteristics, Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), Ultravoilet-Visible (UV–Vis) Spectrophotometry and External Quantum Efficiency (EQE) were employed. The addition of TiO₂ nanoparticles in the active layer improved the power conversion efficiency (PCE) of P3HT:PCBM devices. The addition of TiO₂ nanoparticles using CB as solvent enhanced the absorption in visible region and also introduced a red shift in the absorption spectra. A significant increase in EQE was observed for devices with TiO₂ nanoparticles in the active layer. Mixing TiO₂ also increased the surface roughness of the active layer where TiO₂ nanoparticles were found to agglomerate as their concentration increased relative to fullerene derivative. A complete agglomeration of TiO₂ was observed in the absence of PCBM.     

Two intermediate bands solar cells of InGaN/InN quantum dot supracrystals

Two intermediate bands solar cells (2-IBSC) of In _x Ga_1?x N/InN cubic quantum dot supracrystals were designed in this work. Position and width of the two IBs were determined, the performance parameters including short circuit current density, open circuit voltage and photoelectric conversion efficiency were numerically calculated, and their variations with adjustable variables such as In content, average size of QDs and interdot spacing were further discussed. Within a certain range, the influence from these adjustable variables on the first IB stronger than that on the second one was indicated. The cause of the maximum efficiency in the present cell lower than the one of another 2-IBSC with different material [Jenks and Gilmore, J Renew Sustain Energy 2:013111 (2010)] was probed, while the reason for the maximum efficiency of the studying device near to that of 1-IBSC with same material [Zhang and Wei, Appl Phys A 113:75 (2013)] was clarified.