Incorporation of silver and gold nanostructures for performance improvement in P3HT: PCBM inverted solar cell with rGO/ZnO nanocomposite as an electron transport layer

Inefficient light absorption and inefficient charge separation are considered as two major impediments for the efficiency improvement in bulk heterojunction organic solar cells (BHJ OSCs). In this work, we report the simultaneous role of modified electron transport layer (ETL) and photoactive layers on the performance of poly (3-hexylthiophene), [6, 6]-phenyl C61-butyric acid methyl ester (P3HT: PCBM) BHJ OSCs. To modify the ETL, composite of reduced graphene oxide (rGO) (0.4 wt %) and ZnO nanoparticles (NPs) was used, which resulted in efficiency enhancement from 3.13 to 3.81%, as compared to a value of 3.13% when only ZnO was used. Thereafter, to improve upon the optical absorption properties, the photoactive layer is modified by embedding nanoparticles and nanorods of Ag and Au into it. The size of Ag and Au nanoparticles were chosen to be 50 nm while the dimensions of Ag and Au nanorods were so controlled to obtain length of approx. 50 nm and width of ∼10 nm. All the devices were fabricated in inverted geometry and 20 wt% nanostructures embedded devices showed the best results. For Ag and Au NPs embedded devices, the maximum power conversion efficiency was found to be 4.21% and 4.44%, respectively. On the other hand, for Ag and Au NRs embedded devices, the maximum efficiency was 4.37% and 4.85%, respectively. For comparison, the control devices where no nanostructures were embedded, which shows efficiency of 3.81%. Therefore, an overall enhancement in efficiency was nearly 1.21 and 1.1, 1.16, 1.14, 1.27 fold after modifying ETL as well as the active layer. The reasons for performance improvement were ascribed to better charge extraction properties of ETL, enhanced light absorption due to localized surface plasmon resonance (LSPR) and efficient light scattering by the nanostructures and improved global mobilities.     

Incorporation of SiO2 dielectric nanoparticles for performance enhancement in P3HT:PCBM inverted organic solar cells

It is well known that organic solar cells (OSCs) with inverted geometry have not only demonstrated a better stability and longer device life time but also have shown improved power conversion efficiency (PCE). Recent studies exhibit that incorporation of metal and/or semiconducting nanoparticles (NPs) can further increase the PCE for OSCs. In this present work, we have synthesized SiO₂ NPs of various sizes (25, 50, 75 and 100 nm) using the modified Stober method and incorporated them into P3HT:PCBM photoactive layer and ZnO based electron transport layer (ETL) in order to investigate the light trapping effects in an OSC. Absorption studies have shown a considerable increase in photo absorption in both cases. The fabricated devices demonstrated 13% increase in the PCE when SiO₂ NPs are incorporated in P3HT:PCBM photoactive layer, whereas PCE was increased by 20% when SiO₂ NPs are incorporated in ZnO based ETL. Mott–Schottky analysis and impedance spectroscopy measurements have been carried out to determine the depletion width and global mobility for both the devices. The possible reason for PCE enhancement and the role of SiO₂ NPs in active layer and ZnO ETL are explained on the basis of the results obtained from Mott–Schottky analysis and impedance spectroscopy measurements.     

Localized Surface Plasmon Resonance Enhanced Photocatalytic Hydrogen Evolution via Pt@Au NRs/C3N4 Nanotubes under Visible‐Light Irradiation

Au nanorods (NRs) decorated carbon nitride nanotubes (Au NRs/CNNTs) photocatalysts have been designed and prepared by impregnation–annealing approach. Localized surface plasmon resonance (LSPR) peaks of Au NRs can be adjusted by changing the aspect ratios, and the light absorption range of Au NRs/CNNTs is extended to longer wavelength even near‐infrared light. Optimal composition of Pt@Au NR₇₆₉/CNNT₆₅₀ has been achieved by adjusting the LSPR peaks of Au NRs and further depositing Pt nanoparticles (NPs), and the photocatalytic H₂ evolution rate is 207.0 µmol h^?1 (20 mg catalyst). Preliminary LSPR enhancement photocatalytic mechanism is suggested. On one hand, LSPR of Au NRs is beneficial for visible‐light utilization. On the other hand, Pt NPs and Au NRs have a synergetic enhancement effect on photocatalytic H₂ evolution of CNNTs, in which the local electromagnetic field can improve the photogenerated carrier separation and direct electron transfer increases the hot electron concentration while Au NRs as the electron channel can well restrain charge recombination, finally Pt as co‐catalyst can boost H⁺ reduction rate. This work provides a new way to develop efficient photocatalysts for splitting water, which can simultaneously extend light absorption range and facilitate carrier generation, transportation and reduce carrier recombination.     

High-efficiency inverted polymer solar cells via dual effects of introducing the high boiling point solvent and the high conductive PEDOT:PSS layer

Polymer solar cells (PSCs) are of great interest in the past decade owing to their potentially low-cost in the manufacturing by the solution-based roll to roll method. In this paper, a novel inverted device structure was introduced by inserting a high conductive PEDOT:PSS (hcPEDOT:PSS) layer between the Au nanoparticles (NPs)-embedded hole transport layer (PEDOT:PSS) and the top electrode layer. Power conversion efficiency (PCE) initially reached up to 4.51%, illustrating ∼10% higher compared with the device similarly enhanced by Au NPs plasmonics where only one PEDOT:PSS layer with the embedded Au NPs was used in single bulk heterojunction inverted PSCs based on the poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methylester (P3HT:PCBM). The PCE was further improved from 4.51% to 5.01% by adding the high-boiling point solvent of 1,8-diiodooctane (DD) into the active layer, presenting ∼20% enhancement in PCE through dual effects of introducing the high boiling point solvent and the high conductive PEDOT:PSS layer. Morphologies of the active layers were characterised by SEM and AFM separately in the paper.     

等离激元共振增强多晶硅薄膜太阳电池性能研究

采用磁控溅射方法,在多晶硅薄膜太阳电池表面沉积了不同粒径大小的Au纳米粒子,利用粒径大小可调控的Au纳米粒子的局域表面等离激元共振增强效应(LSPR),对入射光中的可见光区域实现“光俘获”;采用UV-vis吸收光谱对LSPR进行了研究,结果表明,LSPR能够有效拓展Au纳米粒子的光谱响应范围(400～800 nm),并且,随着Au纳米粒子粒径的增大,LSPR共振吸收峰呈现出明显“红移”;同时,通过SERS表征,证实LSPR能够有效增强Au纳米粒子周围的局域电磁场强度;最后,多晶硅太阳电池的J-V特性曲线表明,当Au纳米粒子溅射时间为50 s时,多晶硅太阳电池光电转换效率(η)最高为14.8％,比未修饰Au纳米粒子的电池η提高了42.3％.     

Enhanced carrier mobility and photon-harvesting property by introducing Au nano-particles in bulk heterojunction photovoltaic cells

In this study, polymer solar cells (PSCs) doped with Au nanoparticles (Au NPs) were successfully fabricated to maximize the photon-harvesting properties on the photoactive layer. In addition, a conductivity-enhanced hybrid buffer layer was introduced to improve the photon absorption properties and effectively separate the generated charges by adding Au NPs and dimethylsulfoxide (DMSO) to the PH 500 as a buffer layer. The PSC performance was optimized with a 88% improvement over the conventional PSCs (photoactive area: 225 mm², power conversion efficiency (PCE): 3.2%) by the introduction to the buffer layer of Au NPs and DMSO at 10 wt% and 1.0 wt%, respectively, and with 15 wt% Au NP doping in the photoactive layer. The internal resistance was decreased due to the increased photocurrent caused by the localized surface plasmon resonance (LSPR) effect of the Au NPs in the photoactive layer and by the improvement of carrier mobility induced by the DMSO doping of the buffer layer. As a result, the series resistance (R_S) deceased from 42.3 to 19.7 Ω cm² while the shunt resistance (R_SH) increased from 339 to 487 Ω cm².     

Interfacial engineering of ZnO nanoarrays as electron transport layer for polymer solar cells

Highly uniform one-dimensional ZnO nanoarrays (ZnO NAs) fabricated by hydrothermal process were successfully explored as electron transport layer (ETL) for offering a direct and efficient path for electron transport in inverted polymer solar cells (PSCs). The inorganic CdS shell layer by in situ growth on the ZnO NAs surface was used to passivate and repair the surface defects of ZnO NAs. To further engineer the ZnO surface and improve the compatibility between ETL of inorganic ZnO/CdS core/shell and polymer blend contact junction, those organic molecules of 3,6,7,10,11-pentakis-(hexyloxy)-2-hydroxytriphenylene (TP-OH), 1-pyrenol (Py-OH) and 4′-(7-hydroxy-heptanoyl)-biphenyl-4-carbonitrile (BP-OH) were respectively spin-coated on the ZnO NAs/CdS surface to fabricate ETL based on ZnO/CdS/TP-OH NAs, ZnO/CdS/Py-OH NAs, ZnO/CdS/BP-OH NAs. The π–π interactions between the organic molecules and fullerene acceptors could lead to the well-organized distribution of active layer materials, which is in favor of the enhancement of electron selectivity and the reduction of recombination probability of electrons and holes. The incorporation of ZnO/CdS/Py-OH NAs as ETL into the inverted PSCs based on P3HT:PC₆₁BM resulted in a superior power conversion efficiency (PCE) of 4.2% with enhanced short circuit current (J_sc) and fill factor (FF), compared to 3.1% for bare ZnO NAs, due to the intermolecular close-stacking and relative stronger π–π interaction energy between Py-OH and fullerenes. In addition, the sensitized ZnO surface led to intimate interface between ETL and active layer, which would be in favor of increasing the stability of the device.     

TBP precursor agent passivated ZnO electron transport layer for highly efficient polymer solar cells

Defects passivation in electron transport layer (ETL) is a key issue to optimize the performance of polymer solar cells (PSCs). In this work, a novel strategy is developed to form defects passivated ZnO ETL by introducing 4-tert-butylpyridine (TBP) agent into precursor. While the power conversion efficiency (PCE) of the inverted PSCs based poly{4,8-bis [(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno [3,4-b]thiophene-4,6-diyl}:[6,6]-phenyl C71-butyric acid methyl ester (PTB7:PC₇₁BM) with the pure ZnO ETL is 8.02%, that of the device with modified ZnO ETL is dramatically improved to 10.26%, with TBP accounting for ~28% efficiency improvement. Our study demonstrates that the precursor agent significantly affect the surface morphology and size of ZnO in ETL. Furthermore, it proves that the ZnO ETL with TBP (T-ZnO) is beneficial to polish interfacial contact between ETL and active layer and depress exciton quenching loss, resulting in enhanced exciton dissociation, efficient carrier collection and reduced charge recombination, thus improving the device performance. To verify the universality of T-ZnO ETL, the champion photovoltaic performance with a PCE of 11.74% (10% improvement) is obtained in the PBDB-T-2F:IT-4F based nonfullerene PSCs using T-ZnO as ETL. Our work developed a new, universal and facile strategy for designing highly efficient PSCs based on fullerene and nonfullerene blend systems.     

The dual localized surface plasmonic effects of gold nanodots and gold nanoparticles enhance the performance of bulk heterojunction polymer solar cells

In this study, we investigated the effects of plasmonic resonances induced by gold nanodots (Au NDs), thermally deposited on the active layer, and octahedral gold nanoparticles (Au NPs), incorporated within the hole transport layer, on the performance of bulk heterojunction polymer solar cells (PSCs) based on poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl-C₆₁butyric acid methyl ester (PC₆₁BM). Thermal deposition of 5.3-nm Au NDs between the active layer and the cathode in a P3HT:PC₆₁BM device resulted in the power conversion efficiency (PCE) of 4.6%—that is 15% greater than that (4.0%) for the P3HT:PC₆₁BM device without Au NDs. The Au NDs provided near-field enhancement through excitation of the localized surface plasmon resonance (LSPR), thereby enhancing the degree of light absorption.     

Enhancement of the power conversion efficiency for organic photovoltaic devices due to an embedded rugged nanostructural layer

Organic photovoltaic (OPV) cells utilizing a rugged nanostructural layer were fabricated by using a mixed solution method. The charge separation at the heterointerface between the poly(3-hexylthiophene) (P3HT) nanostructural layer with a rugged surface and the C60 layer was increased due to an increase in the interfacial region between the donor and the acceptor layers, resulting in an increase in the short-circuit current density and the power conversion efficiency (PCE) of the OPV cells with a P3HT nanostructural layer. The PCE of the OPV cells with a nanostructural rugged layer is 30% higher than that without a rugged layer.     

Improved photovoltaic characteristics of organic cells with heterointerface layer as a hole-extraction layer inserted between ITO anode and donor layer

We have fabricated an improved organic photovoltaic (OPV) cell in which organic heterointerface layer is inserted between indium-tin-oxide (ITO) anode and copper-phthalocyanine (CuPc) donor layer in the conventional OPV cell of ITO/CuPc/fullerene (C₆₀)/bathophenanthroline (Bphen)/Al to enhance the power conversion efficiency (PCE) and fill factor (FF). The inserted ITO-buffer layer consists of electron-transporting layer (ETL) and hole-transporting layer (HTL). We have changed the ETL and HTL materials variously and also changed their layer thickness variously. It is confirmed that ETL materials with higher LUMO level than the work function of ITO give low PCE and FF. All the double layer buffers give higher PCE than a single layer buffer of TAPC. The highest PCE of 1.67% and FF of 0.57% are obtained from an ITO buffer consisted of 3 nm thick ETL of hexadecafkluoro-copper-phthalocyanine (F₁₆CuPc) and 3 nm thick HTL of 1,1-bis-(4-methyl-phenyl)-aminophenylcyclohexane (TAPC). This PCE is 1.64 times higher than PCE of the cell without ITO buffer and 2.98 times higher than PCE of the cell with single layer ITO buffer of TAPC. PCE is found to increase with increasing energy difference (ΔE) between the HOMO level of HTL and LUMO level of F₁₆CuPc in a range of ΔE < 0.6 eV. From the ΔE dependence of PCE, it is suggested that electrons moved from ITO to the LUMO level of the electron-transporting F₁₆CuPc are recombined, at the F₁₆CuPc/HTL-interface, with holes transported from CuPc to the HOMO level of HTL in the double layer ITO buffer ETL, leading to efficient extraction of holes photo-generated in CuPc donor layer.     

Enhanced power conversion efficiency of organic photovoltaic devices due to the surface plasmonic resonance effect generated utilizing Au-WO3 nanocomposites

Au-WO₃ nanocomposites (NCs) were used as a hole transport layer (HTL) to enhance the power conversion efficiency (PCE) of organic photovoltaic (OPV) cells. The photon absorption of the active layer in the OPV cells was increased due to the plasmonic effect caused by the Au-WO₃ NCs, resulting in an enhanced short-circuit current density for the OPV cells with the Au-WO₃ NC HTL. The value of the root-mean-square roughness of the Au-WO₃ NC film was smaller than that of the WO₃ NP film, resulting in a more efficient transport of holes from the active layer. The PCE of the OPV cell with an Au-WO₃ NCs HTL with an Au NP concentration of 10 wt% was improved by 60.37% in comparison with that with WO₃ nanoparticles. The enhancement of the PCE was attributed to both an increase in the efficiency of the hole transport at an Au-WO₃ NCs HTL with an Au NP concentration of 10 wt%/active layer heterointerface and an enhanced photon absorption due to the localized surface plasmon resonance effect of the Au-WO₃ NCs.     

Solution-processed annealing-free ZnO nanoparticles for stable inverted organic solar cells

We report the development and application of high-quality zinc oxide nanoparticles (ZnO NPs) processed in air for stable inverted bulk heterojunction solar cells as an electron extraction layer (EEL). The ZnO NPs (average size ∼11 nm) were dispersed in chloroform and stabilized by propylamine (PA). We demonstrated that the ZnO NP dispersion with 4 vol.% of PA as stabilizer can be used in air directly and remains clear up to one month after preparation. Our inverted solar cells consisted of a blade-coated poly(N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole (PCDTBT) and [6,6]-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) (1: 4 by weight) active layer sandwiched between a ZnO electron extraction layer and a MoO₃/Ag anode. All solar cells with ZnO films fabricated in air using PA-stabilized ZnO dispersions prepared within a time window of one month exhibited power conversion efficiencies (PCE) above 4%. In contrast, if the ZnO film was prepared in air using regular un-stabilized ZnO NP dispersion, the PCE would drop to 0.2% due to poor film quality. More interestingly, X-ray photoelectron spectroscopy and nuclear magnetic resonance measurements indicated that the PA ligands were not covalently bonded to ZnO NPs and did not exist in the deposited ZnO films. The spin-cast ZnO thin films (without any thermal treatment) are insoluble in organic solvents and can be directly used as an EEL in solar cells. This feature is beneficial for fabricating organic solar cells on flexible polymer substrates. More importantly, our non-encapsulated inverted solar cells are highly stable with their PCEs remaining unchanged after being stored in air for 50 days.     

Performance enhancement in inverted polymer solar cells incorporating ultrathin Au and LiF modified ZnO electron transporting interlayer

The performance enhancement of inverted polymer solar cells (PSCs), based on the blend system of regioregular poly(3-hexylthiophene) and [6,6]-phenyl C₆₁-butyric acid methylester, due to incorporating ultrathin Au and LiF interlayer between the front transparent indium tin oxide and a ZnO electron transporting layer was analyzed. The results reveal that a 40% increase in PCE, e.g., from 2.62% to 3.67%, was observed for PSCs made with an optimal Au/LiF interlayer as compared to the one having a bare ZnO electron transporting layer. The presence of Au/LiF-modified ZnO interlayer between ITO and the organic layer helps to improve the charge collection. The absorption enhancement arising from the plasmon resonance of Au nanostructures also contributed to the improvement in PCE. It is shown that PSCs with LiF incorporated ZnO electron transporting layer allow improving cell lifetime, demonstrating <50% decrease in PCE compared to that of the ones with a bare ZnO interlayer after 240 day aging test for cells without encapsulation in air.     

Role of fullerene electron transport layer on the morphology and optoelectronic properties of perovskite solar cells

High performance, hysteresis-free, low temperature n-i-p perovskite solar cells are successfully fabricated by solution processing using fullerene electron transport layer (ETL). PC₇₁BM fullerene, with broader absorption spectrum and lower HOMO level, when incorporated in the perovskite solar cell yielded average power conversion efficiency (PCE) of 13.9%. This is the highest reported PCE in n-i-p perovskite solar cells with PC₇₁BM ETL. The devices exhibited negligible hysteresis and high open-circuit voltage (V_oc). On the contrary, devices with PC₆₁BM, a common fullerene ETL in perovskite solar cell, exhibited large hysteresis and lower V_oc. The underlying mechanisms of superior performance of devices with PC₇₁BM ETL were found to be correlated with fullerene surface wettability and perovskite grain size. The influence of fullerene ETL on the perovskite grain growth and subsequent photovoltaic performance was investigated by contact angle measurement, morphological characterization of the surface topography and electrochemical impedance analysis.     

Enhanced Charge Separation Efficiency in DNA Templated Polymer Solar Cells

The insertion of a DNA nanolayer into polymer based solar cells, between the electron transport layer (ETL) and the active material, is proposed to improve the charge separation efficiency. Complete bulk heterojunction donor–acceptor solar cells of the layered type glass/electrode (indium tin oxide)/ETL/P3HT:PC₇₀BM/hole transport layer/electrode (Ag) are investigated using femtosecond transient absorption spectroscopy both in the NIR and the UV–vis regions of the spectrum. The transient spectral changes indicate that when the DNA is deposited on the ZnO nanoparticles (ZnO‐NPs) it can imprint a different long range order on the poly(3‐hexylthiophene) (P3HT) polymer with respect to the non‐ZnO‐NPs/DNA containing cells. This leads to a larger delocalization of the initially formed exciton and its faster quenching which is attributed to more efficient exciton dissociation. Finally, the temporal response of the NIR absorption shows that the DNA promotes more efficient production of charge transfer states and free polarons in the P3HT cation indicating that the increased exciton dissociation correlates with increased charge separation.     

Plasmonic Au nanoparticles for enhanced broadband light absorption in inverted organic photovoltaic devices by plasma assisted physical vapour deposition

We use a low vacuum plasma assisted physical vapour deposition (PAPVD) method to deposit a Au nanoparticles (NPs) thin film onto the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer in inverted poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methylester (P3HT:PCBM) organic photovoltaic (OPV) devices. The Au NPs that incorporated into the PEDOT:PSS layer and reached to the active P3HT:PCBM layer can provide significant plasmonic broadband light absorption enhancement to the active layer. An approximately 50–90% improvement in short-circuit current density and in power convention efficiency has been achieved compared with those OPV devices without the plasmonic light absorption enhancement. This technique can be adopted and easily fit into most OPV device fabrication processes without changing other layers’ processing methods, morphologies, and properties.     

Spatial Extent of Fluorescence Quenching in Mixed Semiconductor–Metal Nanoparticle Gel Networks

In this work, mixing and co-gelation of Au nanoparticles (NPs) and highly luminescent CdSe/CdS core/shell nanorods (NRs) are used as tools to obtain noble metal particle-decorated macroscopic semiconductor gel networks. The hybrid nature of the macrostructures facilitates the control over the optical properties: while the holes are trapped in the CdSe cores, the connected CdSe/CdS NRs support the mobility of excited electrons throughout the porous, hyperbranched gel networks. Due to the presence of Au NPs in the mixed gels, electron trapping in the gold NPs leads to a suppressed radiative recombination, namely, quenches the fluorescence in certain fragments of the multicomponent gel. The extent of fluorescence quenching can be influenced by the quantity of the noble metal domains. The optical properties are monitored as a function of the NR:NP ratio of a model system CdSe/CdS:Au. By this correlation, it demonstrates that the spatial extent of quenching initiated by a single Au NP exceeds the dimensions of one NR, which the Au is connected to (with a length of 45.8 nm ± 4.1 nm) and can reach the number of nine NRs per Au NP, which roughly corresponds to 400 nm of total electron travel distance within the network structure.     

Broad-band plasmonic Cu-Au bimetallic nanoparticles for organic bulk heterojunction solar cells

In this work, a facile preparation of Cu-Au bimetallic nanoparticles (NPs) with core-shell nanostructures is reported. Importantly, as-prepared Cu-Au NPs are highly stable, solution-processable and exhibit a broad localized surface plasmon resonance (LSPR) band at long wavelengths of 550–850 nm. Highly efficient plasmonic organic solar cells (OSCs) were fabricated by embedding Cu-Au NPs in an anodic poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer. The average power conversion efficiency (PCE) was enhanced from 3.21% to 3.63% for poly(3-hexylthiophene) (P3HT):phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) based devices, from 6.51% to 7.13% for poly[(ethylhexyl-thiophenyl)-benzodithiophene -(ethylhexyl)-thienothiophene](PTB7-th):PC₆₁BM based devices and from 7.53% to 8.48% for PTB7-th:PC₇₁BM based devices, corresponding to 9.5–13.4% PCE improvement. Such an improvement is very comparable to that (12.5%) obtained in those with plasmonic Au NPs but achieved at lower cost. This study thus demonstrates a novel and cost-effective approach to enhance the photovoltaic performance of OSCs, in combination with the broad-band plasmonic Cu-Au bimetallic nanostructures.     

Synthesis of ZnO nanostructure films by thermal evaporation approach and their application in dye-sensitized solar cells

Zinc oxide (ZnO) films were prepared successfully by simple thermal evaporation of zinc acetate dihydrate at low temperature onto FTO (fluorine-doped tin oxide) glass substrates coated with thin ZnO seed layer. The synthetic parameter such as temperature was found to determine the morphology of nanostructures. ZnO nanorod (NR) and nanoparticle (NP) films have been synthesized at 245 and 350 °C, respectively, for 6 h. The dye-sensitized solar cells (DSSCs) were fabricated using the ZnO nanostructure films as photosensitized electrodes. A maximum photoelectric conversion efficiency (PCE) of 1.56%, and short-circuit photocurrent density of 5.12 mA/cm² were achieved with the ZnO NP-based DSSC. The PCE increase was ascribed to the reduced recombination loss and prolonged electron lifetime according to electrochemical impedance spectroscopy (EIS).