Inverted Polymer Solar Cells Research Articles

Advancing stability in inverted polymer solar cells through accelerated xenon curing of the ZnO layer

This study delves into the profound implications of employing an intensive xenon lamp treatment with a rapid curing method completed within 4 min, to fabricate a ZnO layer. Subsequently, we applied a coating of PM6:Y6 as the active layer and utilized MoO3/Ag as the contact electrode, aiming to advance the efficiency of polymer solar cells (PSCs) through entirely room-temperature processes. Our investigation juxtaposes this xenon lamp treatment with the conventional hot plate method for annealing the ZnO layer, conducted at 180 °C for both 20 min and 4 min. Remarkably, our proposed xenon lamp treatment process not only promotes charge transfer but also exhibits enhancements of the lattice oxygen in the Zn-O layer. This innovative methodology of xenon treatment yields a notable increase in power conversion efficiency (PCE), achieving 14.55 %, compared to 13.71 % and 12.44 % for the ZnO layers annealed with a hot plate for 20 min and 4 min, respectively. Moreover, devices subjected to the 4-min xenon lamp treatment maintained 85 % (T85) of their original Power Conversion Efficiency (PCE) after enduring 500 h of one-sun aging measurement. These findings evoke optimism regarding the xenon treatment's potential to streamline the fabrication process, and provide a promising avenue for mitigating interface degradation while enhancing the stability of PSCs.

Fibril ZnO as an Electron Transporting Layer for Enhancing the Photovoltaic Performance of Inverted Polymer Solar Cells Based on Nonfullerene Acceptors

Fibril ZnO as an Electron Transporting Layer for Enhancing the Photovoltaic Performance of Inverted Polymer Solar Cells Based on Nonfullerene Acceptors

Enhanced performance of inverted polymer solar cells by adding benzyl viologen dichloride into ZnO electron transport layer

An organic-inorganic hybrid electron transport layer (ETL) is developed using benzyl viologen dichloride (BV–2Cl) as a dopant for the preparation of sol-gel ZnO precursor solution. The inverted polymer solar cells (I–PSCs) based on PTB7-Th:PC71BM were prepared by introducing hybrid ZnO:BV-2Cl as ETL, and the effect of BV-2Cl on the photovoltaic performance of PSCs was closely investigated. Consequently, the device with hybrid ZnO:BV-2Cl (1% wt%) as ETL achieves the power conversion efficiency (PCE) of 9.31%, which is 16.5% more efficient than the device using pure ZnO as ETL. As the results indicate, hybrid ZnO:BV-2Cl films can modulate the interfacial compatibility of the hydrophilic surface of conventional ZnO films, hence enhancing charge transport and exciton dissociation. Our results indicate that using BV-2Cl as a dopant for the preparation of ZnO ETL is a facile and efficient method of fabricating high-performance I–PSCs.

Combining ZnO and Organosilica Nanodots as a Thick Cathode Interlayer for Highly Efficient and Stable Inverted Polymer Solar Cells

Low-work-function metal oxides as cathode interlayers are widely used in polymer organic solar cells (PSCs), but the surface defect and intrinsic photocatalysis issues severely affect the high efficiency, thickness insensitivity, and stability of PSCs. In this work, we used organosilica nanodots (OSiNDs) to modify ZnO as cathode interlayers via the self-assembly method. The ZnO/OSiNDs bilayer can acquire a suitable work function and a high conductivity of 5.87 × 10–4 S m–1. Through systematic studies, there is stable surface coordination interaction of Zn–N bonding between ZnO and OSiNDs. In i-PSCs, using D18:Y6 as the active layer, the ZnO/OSiNDs-based device achieves the best PCE of 17.87%. More importantly, due to the high conductivity, the PCE for the device based on a 68 nm thick ZnO/OSiNDs interlayer is still high up to 16.53%, while the PCE for the device based on a 66 nm thick ZnO interlayer is only 13.18%. For photostability, the PCE of the device based on the ZnO/OSiNDs interlayer maintains 95% of its original value after continuous AM 1.5G illumination (contains UV light) at 100 mW/cm2 for 600 min, while that of the ZnO-based device only maintains 72% of the original value. This work suggests that ZnO/OSiNDs can be utilized as a cathode interlayer to fabricate highly efficient and stable PSC over a wide range of thicknesses.

Synthesis and characterization of novel conjugated polymer based on indacenetetraone as the electron acceptor and its photovoltaic properties

The donor-conjugated polymer named PBDT-IDE-BOT has been successfully synthesized and characterized for inverted polymer solar cell (iPSC). The polymer compromise benzodithiophene (BDT) as donor unit, indacenetetraone (IDE) as acceptor unit, and butyl octyl thiophene (BOT) as π-bridge. The polymer shows broad absorption, and its optical band gap of PBDT-IDE-BOT was 1.64 eV. The HOMO and LUMO energy level of PBDT-IDE-BOT were −5.18 and −3.57 eV, respectively. We fabricated the iPSCs based on PC71BM, ITIC, and Y6BO. The inverted PSC based on PBDT-IDE-BOT/PC71BM, PBDT-IDE-BOT/ITIC, and PBDT-IDE-BOT/Y6BO showed a power conversion efficiency (PCE) of 2.05, 0.5, and 0.19%, respectively.

Dramatic improvement in the stability and mechanism of high-performance inverted polymer solar cells featuring a solution-processed buffer layer.

In this study, we demonstrate inverted PTB7:PC71BM polymer solar cells (PSCs) featuring a solution-processed s-MoO3 hole transport layer (HTL) that can, after thermal aging at 85 °C, retain their initial power conversion efficiency (PCE) for at least 2200 h. The T80 lifetimes of the PSCs incorporating the novel s-MoO3 HTL were up to ten times greater than those currently reported for PTB7- or low-band-gap polymer:PCBM PSCs, the result of the inhibition of burn-in losses and long-term degradation under various heat-equivalent testing conditions. We used X-ray photoelectron spectroscopy (XPS) to study devices containing thermally deposited t-MoO3 and s-MoO3 HTLs and obtain a mechanistic understanding of how the robust HTL is formed and how it prevented the PSCs from undergoing thermal degradation. Heat tests revealed that the mechanisms of thermal inter-diffusion and interaction of various elements within active layer/HTL/Ag electrodes controlled by the s-MoO3 HTL were dramatically different from those controlled by the t-MoO3 HTL. The new prevention mechanism revealed here can provide the conceptual strategy for designing the buffer layer in the future. The PCEs of PSCs featuring s-MoO3 HTLs, measured in damp-heat (65 °C/65% RH; 85 °C per air) and light soaking tests, confirmed their excellent stability. Such solution-processed MoO3 HTLs appear to have great potential as replacements for commonly used t-MoO3 HTLs.

Comparative study on the electrochemical synthesis of zinc oxide nanorods using chronoamperometry and chronopotentiometry and their application in inverted polymer solar cells

In this work, the influences of zinc oxide nanorods (ZnO NRs) arrangement, as the electron transport layer (ETL), on the photovoltaic performance of the inverted structure polymer solar cells (PSCs) were studied. Two arrangements of ZnO NRs were electrochemically synthesized on the indium tin oxide (ITO) electrode by chronoamperometry (CA) and chronopotentiometry (CP) techniques at 80 °C. Structural, morphological, optical, and electrochemical features of the prepared samples were compared using different techniques. Applying the CA technique resulted in the vertical growth of ZnO NRs on the ITO electrode. However, flower-like ZnO NRs were formed in the sample prepared by the CP method. The energy levels, charge transfer resistance, recombination resistance, and charge mobility of the prepared samples were evaluated using cyclic voltammetry and electrochemical impedance spectroscopy. Results revealed that the flower-like ZnO NRs prepared by the CP method enjoy a considerably higher (128%) charge mobility of 31.67 × 10−4 cm2/V, lower (17.6%) charge resistance of 32.82 Ω, and higher optical transparency of ∼75.52% at 550 nm. The PSC prepared based on the flower-like ZnO NRs provided a PCE of 4.45, which was about 230.57%, 145.42%, and 302.72% higher than that achieved for the ZnO nanoparticles-, and the vertical ZnO NRs-based devices, and the reference device containing no ETL. Moreover, the flower-like ZnO NRs-based PSC exhibited greater stability in the air and retained about 72% of its initial PCE after 450 h.

Conventional and Metal Oxide-Based Inverted Polymer Solar Cells: A Comparative Experimental Study

Conventional and Metal Oxide-Based Inverted Polymer Solar Cells: A Comparative Experimental Study

Conjugated oxazole‐based interfacial materials for efficient and stable inverted polymer solar cell with an efficiency of 16.52%

Organic solar cells (OSCs) using non-fullerene acceptors have delivered the highest efficiencies in the overall reported literatures. In order to improve the efficiency and stability of OSCs, great efforts are being made in designing and synthesizing new materials. Inverted OSCs were fabricated using three commercially available and inexpensive materials, 5-methylbenzoxazole (E1), 2-(4-biphenyl)-5-phenyloxazole (E2), and 4-bis(5-phenyl-2-oxazolyl)benzene (E3), as an interlayer between zinc oxide and the active layer. The new interlayer materials enhance the carrier injection/extraction properties and thus, the polymer solar cells (PSCs) exhibited an improved JSC and power conversion efficiency (PCE). PSCs showed an improved JSC of 27.18 from 24.88 mA/cm2 with the introduction of E3. The new interlayer, E3 in particular, forms well-aligned cascading energy levels between the PM6:Y6 active layer and zinc oxide layer. These cascading energy levels reduce the energy barrier for electron injection and collection at the interface. Thus, the PCE of devices reached a remarkable 16.52% using interlayer at the ZnO/active layer interface. The devices also exhibited improved device stability under continuous illumination, annealing, and high humidity.

Competitive charge transport processes in inverted polymer solar cells based on ZnO thin films

Competitive charge transport processes in inverted polymer solar cells based on ZnO thin films

16.5% Polymer Solar Cells with 6‐Aminocaproic Acid‐Modified ZnO as a Cathodic Interface Layer

Cathodic interface layers are important in determining the charge carrier collection and performance of polymer solar cells (PSCs). In this work, 6‐aminocaproic acid (6‐ACA) is successfully incorporated into sol–gel‐derived zinc oxide (ZnO) to form 6‐ACA‐ZnO that can be used as a cathodic interface layer (CIL) in PM6:Y6 inverted polymer solar cells (i‐PSCs). The work function of ZnO films can be reduced from 4.53 to 4.10 eV, thus effectively increasing the built‐in electric field and enhancing the electron extraction efficiency. Furthermore, the partial substitution of undercoordinated oxygen vacancy by nitrogen atoms can effectively passivate the interface defects, thereby substantially increasing the electron mobility and conductivity to facilitate electron transport and reduce the carrier recombination loss. The i‐PSCs based on 6‐ACA‐ZnO exhibit a power conversion efficiency (PCE) up to 16.50%, which is remarkably higher than the 15.30% of devices based on pristine ZnO. 6‐ACA‐ZnO can also be successfully applied to other nonfullerene and fullerene‐based i‐PSCs. The results indicate that 6‐ACA‐ZnO can be used as CILs to effectively improve the PCE of i‐PSCs.

A Multifunctional Tyrosine‐Immobilized PAH Molecule as a Universal Cathode Interlayer Enables High‐Efficiency Inverted Polymer Solar Cells (Advanced Optical Materials 21/2021)

A Multifunctional Tyrosine‐Immobilized PAH Molecule as a Universal Cathode Interlayer Enables High‐Efficiency Inverted Polymer Solar Cells (Advanced Optical Materials 21/2021)

Easily Prepared Transparent Electrodes for Low-Cost Semitransparent Inverted Polymer Solar Cells

The continuous thin film of silver (Ag) film is important for semitransparent electrodes in polymer solar cells, while the Ag atoms form as non-continuous below a critical thickness. Here, semitransparent inverted polymer solar cells were fabricated using thermally evaporated Ag/germanium (Ge)/Ag as highly transparent electrodes. An ultra-thin Ge film was introduced to modify the growth mode of Ag. The dependence of the device performance and the thickness of the outer Ag film was investigated. Ag/Ge/Ag electrodes exhibited excellent optical and electrical properties, which were proved by the transmittance and reflectance spectra. A champion efficiency of 5.1% was achieved with an open-circuit voltage level of 0.703 V, a short current density of 11.63 mA/cm2, and a fill factor of 63%. The average visible transmittance (300–800 nm) of devices with Ag/Ge/Ag was calculated as 25%.

Small molecule organic solar cells toward improved stability and performance for Indoor Light Harvesting Application

In this work, we fabricate, characterize and present a stability study of p-DTS(FBTTh 2 ) 2 :PC 70 BM inverted organic solar cells (iOSCs) with two different solution-processed electron transport layers (ETLs), PFN and ZnO, under indoor light and AM 1.5 G illumination spectrum. A warm white color light-emitting diode was used as the indoor light source. Under the luminance of 1000 lux, a maximum power conversion efficiency (PCE) of 10.85% and maximum power density (MPP) of 45.1 μW/cm 2 were obtained for cells with PFN as ETL. After 1536 h of constant indoor light illumination, the PCE remained above 70% of the original value. The best stability of encapsulated devices, under AM 1.5 illumination spectrum was also observed for these cells, which still maintained a PCE above 60% after 6000 h. Performance of small-molecule organic solar cells for Indoor Light Harvesting Application. PFN as electron transport layer for inverted solution-processed small-molecule organic solar cells (SM-iOSC). 1.5 times longer lifetime of encapsulated SM-iOSC versus currently used inverted polymer solar cells (iPSC). Reduced S-shape deformation in the JV curves of HIZO-iOSC vs. PFN-iOSC. Degradation analysis by the solar cells equivalent circuit model.

Enhancing performance of inverted polymer solar cells by an effective novel double layer combining MoO3 and PEIE

Metal oxide of molybdenum oxide (MoO3) and polyethyleneimine ethoxylated (PEIE) was introduced into polymer solar cells (PSCs) as a double interfacial layer. A high power conversion efficiency (PCE) of 3.69% based on poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) was obtained using a MoO3/PEIE bilayer, which is 19.4% higher than that of the pristine devices (the PCE of pristine devices with PEIE interface layer is 3.09%). Results of the analysis via X-ray photoelectron spectroscopy indicated that the MoO3/PEIE bilayer has dual functions. The first function is that MoO3 is successfully transformed into MoO2, enhancing charge transporting. The second function is that the combination of molybdenum oxide and PEIE can be effectively form ohmic contact to reduce interface contact resistance. The measurement of electrochemical impedance and conductivity further illustrated that the MoO3/PEIE double interfacial layer effectively reduced interface contact resistance, promoted charge transport, and enhanced electron transport ability, thereby improving the device performance.

A Multifunctional Tyrosine‐Immobilized PAH Molecule as a Universal Cathode Interlayer Enables High‐Efficiency Inverted Polymer Solar Cells

AbstractAmong the various biological components in the photosynthesis reaction, tyrosine (Tyr) is considered crucial for facilitation of charge/proton transfer. However, the practical realization of this capability in recent artificial solar‐energy conversion systems is limited by the required alignment of Tyr molecules with both host materials and themselves. In this work, Tyr−perylene diimide−Tyr (PDI‐Y) is designed for implementation of a molecular‐based artificial photosystem II, where PDI and Tyr act as an antenna and internal mediator, respectively. The experimental and theoretical investigations prove that the presence of covalently immobilized Tyr can enhance the intramolecular charge separation, leading to a significant reduction of the exciton recombination probability. To explore the feasibility of using Tyr‐immobilized PDI in practical applications, PDI‐Y is applied as a universal cathode interlayer in an inverted polymer solar cell (iPSC). The result demonstrates potential multifunctional roles of PDI‐Y as a sub‐photosensitizer and electron transport layer, leading to a superior photovoltaic performance in both fullerene (PC71BM) and nonfullerene (Y6) based iPSCs. Consequently, the simple yet efficient Tyr‐immobilization approach is expected to offer tremendous opportunities for the advancement of electronic and optoelectronic applications.

ZnO nanoparticles modified with biomaterial GHK-Cu as electron transport layer to fabricate highly efficient inverted polymer solar cells

The interfacial modification with biomaterials is an effective and environmental protection way to improve the efficiency of inverted polymer solar cells (IPSCs) by reducing the defects and interface recombination of ZnO electron transport layer (ETL). In this paper, ZnO surface is successfully modified via Gly-His-Lys-Cu (GHK-Cu), a nontoxic biomaterial, to fabricate novel ZnO&GHK-Cu composite film. The modification of ZnO surface by GHK-Cu makes the Zn-O-Cu bond formed on the surface of ZnO, which provides a channel for the electron transfer from electron-rich functional groups (such as carboxyl, amino and carbonyl) to Zn2+, the electron defects caused by the oxygen vacancies in the ZnO lattice are passivated, which is beneficial to the transfer and extraction of charges in IPSCs. Moreover, the modification of GHK-Cu decreases the chemisorbed oxygen of the surface of ZnO, the height of the Schottky barrier between the ZnO crystal grains is reduced, resulting in an increase in the conductivity of ZnO. The novel ZnO&GHK-Cu composite film has excellent photoelectric properties and IPSCs with new ZnO&GHK-Cu as ETL are fabricated for the first time. As the result, the IPSCs based on PBDB-T:ITIC with ZnO&GHK-Cu as ETL show an optimal power conversion efficiency (PCE) of 11.93%, increases by 15.6% in comparison with ZnO ETL-based IPSCs with a PCE of 10.32%. Meanwhile, the PCE of IPSCs based on PM6:Y6 increases from 14.66% to 16.46%. More interesting, the physical mechanism of improving the performance of IPSCs by modifying of ZnO surface with biomaterial has been deeply analyzed. The work provides an effective method for modification of ZnO surface, also shows that biomaterial GHK-Cu has application prospect in photovoltaic devices.

Inverted Polymer Solar Cells with Annealing-Free Solution-Processable NiO.

Nickel oxide (NiO) offers intrinsic p-type behavior and high thermal and chemical stability, making it promising as a hole transport layer (HTL) material in inverted organic solar cells. However, its use in this application has been rare because of a wettability problem caused by use of water as base solvent and high-temperature annealing requirements. In the present work, an annealing-free solution-processable method for NiO deposition is developed and applied in both conventional and inverted non-fullerene polymer solar cells. To overcome the wettability problem, the typical DI water solvent is replaced with a mixed solvent of DI water and isopropyl alcohol with a small amount of 2-butanol additive. This allows a NiO nanoparticle suspension (s-NiO) to be deposited on a hydrophobic active layer surface. An inverted non-fullerene solar cell based on a blend of p-type polymer PTB7-Th and non-fullerene acceptor IEICO-4F exhibits the high efficiency of 11.23% with an s-NiO HTL, comparable to the efficiency of an inverted solar cell with a MoOx HTL deposited by thermal evaporation. Conventionally structured devices including this s-NiO layer show efficiency comparable to that of a conventional device with a PEDOT:PSS HTL.

Effect of substrate temperature on the charge transport property of Ta2O5 cathode buffer layer in inverted polymer solar cells

Charge extraction ability in inverted polymer solar cells (IPSCs) can be enhanced using thermally evaporated compact Ta2O5 as cathode buffer layer (CBL) deposited onto indium tin oxide (ITO) substrate by varying the substrate temperature from 200 °C to 250 °C. The deposited polycrystalline films exhibit granular morphology with high optical transmittance around 500 nm and significant variation in defects with respect to ITO substrate temperature. Current density–voltage measurements show improvement in power conversion efficiency from 2.8% to 3.1% with ratio/percentage enhancement of 10.7% when substrate temperature is increased from 200 °C to 250 °C.

Investigating the effect of diverse structural variation of conjugated polymer electrolytes as the interlayer on photovoltaic properties

The effect of the diverse structural variation of conjugated polymer electrolytes (CPEs) as an interlayer on the photovoltaic properties was investigated. We found that the CPE with a strong electronegative BT group in the backbone and OH salt group in the side chain offers the highest PCEs among CPEs. • Diverse structural variation of conjugated polymer electrolytes (CPEs). • Step-by-step improvement in efficiency of solar cells based on diverse CPEs as interlayer. • Optical simulations of solar cells using transfer matrix formalism. A series of conjugated polymer electrolytes (CPEs) based on dimethylamino propyl fluorene (FN), thiophene (T), benzothiadiazole (BT), and dithienyl benzothiadiazole (TBT) were synthesized by the Suzuki coupling reaction. Quaternarized polyelectrolytes were obtained from the post-polymerization treatment of the amino-terminal group. The incorporation of electron-rich (T), electron-deficient moiety (BT), and their combination (TBT) in the polymer backbone represent the different effects of polarity. Conjugated backbones are substantially strengthened by varying their electron affinity and conjugated planarity. We systematically investigated the effect of applying CPEs with different backbones and functionalities in the side chain. Different backbones produce different molecular dipoles, and the side chain functionality induces an interfacial dipole. Inverted polymer solar cells (iPSCs) based on a bulk heterojunction (BHJ) were fabricated with the ITO/ZnO/CPE/PTB7-Th:PC 71 BM/MoO 3 /Ag structure. The device performance enhancement was achieved by inserting CPEs as the interlayer. Modifying the polymer backbone leads to improved efficiency and modifying the side chain functionality improves the performance compared with that of the interlayered neutral polymer.