Boosting Performance of Non‐Fullerene Organic Solar Cells by 2D g‐C3N4 Doped PEDOT:PSS

The power‐conversion efficiency (PCE) of single‐junction organic solar cells (OSCs) has exceeded 16% thanks to the development of non‐fullerene acceptor materials and morphological optimization of active layer. In addition, interfacial engineering always plays a crucial role in further improving the performance of OSCs based on a well‐established active‐layer system. Doping of graphitic carbon nitride (g‐C₃N₄) into poly(3,4‐ethylene‐dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer (HTL) for PM6:Y6‐based OSCs is reported, boosting the PCE to almost 16.4%. After being added into the PEDOT:PSS, the g‐C₃N₄ as a Bronsted base can be protonated, weakening the shield effect of insulating PSS on conductive PEDOT, which enables exposures of more PEDOT chains on the surface of PEDOT:PSS core‐shell structure, and thus increasing the conductivity. Therefore, at the interface between g‐C₃N₄ doped HTL and PM6:Y6 layer, the charge transport is improved and the charge recombination is suppressed, leading to the increases of fill factor and short‐circuit current density of devices. This work demonstrates that doping g‐C₃N₄ into PEDOT:PSS is an efficient strategy to increase the conductivity of HTL, resulting in higher OSC performance.     

An ammonia modified PEDOT: PSS for interfacial engineering in inverted planar perovskite solar cells

Poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) is one of the most widely used hole transport layers (HTL) in inverted perovskite solar cells (PSCs) due to its simple solution-processed ability, high transparency, and conductivity. However, PEDOT:PSS-based devices suffer a lower open-circuit voltage (V_oc) than devices with the conventional structure. To address this issue, we fabricated ammonia-modified PEDOT:PSS films by simply doping PEDOT:PSS solution with different ratio of ammonia. The acidity of PEDOT:PSS can be neutralized by the doped ammonia, which inhibits the ion-exchange reaction between PSS-H and CH₃NH₃I, thus retarding the reduction of the work function for PEDOT:PSS to some extent. As a result, a superior power conversion efficiency (PCE) of 15.5% was obtained for the device based on the ammonia-doped PEDOT:PSS HTL than that of the pristine PEDOT:PSS-based device. We ascribe the PCE enhancement to the increased V_oc and fill factor (FF), which is attributed not only to the better energy-level alignment between the ammonia-modified PEDOT:PSS film and perovskite layer but also to the increased grain size and crystallinity of perovskite film.     

Design of Multilayered Nanostructures and Donor–Acceptor Interfaces in Solution‐Processed Thin‐Film Organic Solar Cells

Multilayered polymer thin‐film solar cells have been fabricated by wet processes such as spin‐coating and layer‐by‐layer deposition. Hole‐ and electron‐transporting layers were prepared by spin‐coating with poly(3,4‐ethylenedioxythiophene) oxidized with poly(4‐styrenesulfonate) (PEDOT:PSS) and fullerene (C₆₀), respectively. The light‐harvesting layer of poly‐(p‐phenylenevinylene) (PPV) was fabricated by layer‐by‐layer deposition of the PPV precursor cation and poly(sodium 4‐styrenesulfonate) (PSS). The layer‐by‐layer technique enables us to control the layer thickness with nanometer precision and select the interfacial material at the donor–acceptor heterojunction. Optimizing the layered nanostructures, we obtained the best‐performance device with a triple‐layered structure of PEDOT:PSS|PPV|C₆₀, where the thickness of the PPV layer was 11 nm, comparable to the diffusion length of the PPV singlet exciton. The external quantum efficiency spectrum was maximum (ca. 20%) around the absorption peak of PPV and the internal quantum efficiency was estimated to be as high as ca. 50% from a saturated photocurrent at a reverse bias of ?3 V. The power conversion efficiency of the triple‐layer solar cell was 0.26% under AM1.5G simulated solar illumination with 100 mW cm^?2 in air.     

Efficient and Stable Perovskite Solar Cells via Dual Functionalization of Dopamine Semiquinone Radical with Improved Trap Passivation Capabilities

Highly efficient planar heterojunction perovskite solar cells (PVSCs) with dopamine (DA) semiquinone radical modified poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) (DA‐PEDOT:PSS) as a hole transporting layer (HTL) were fabricated. A combination of characterization techniques were employed to investigate the effects of DA doping on the electron donating capability of DA‐PEDOT:PSS, perovskite film quality and charge recombination kinetics in the solar cells. Our study shows that DA doping endows the DA‐PEDOT:PSS‐modified PVSCs with a higher radical content and greater perovskite to HTL charge extraction capability. In addition, the DA doping also improves work function of the HTL, increases perovskite film crystallinity, and the amino and hydroxyl groups in DA can interact with the undercoordinated Pb atoms on the perovskite crystal, reducing charge‐recombination rate and increasing charge‐extraction efficiency. Therefore, the DA‐PEDOT:PSS‐modified solar cells outperform those based on PEDOT:PSS, increasing open‐circuit voltage (V _oc) and power conversion efficiency (PCE) to 1.08 V and 18.5%, respectively. Even more importantly, the efficiency of the unencapsulated DA‐PEDOT:PSS‐based PVSCs are well retained with only 20% PCE loss after exposure to air for 250 hours. These in‐depth insights into structure and performance provide clear and novel guidelines for the design of effective HTLs to facilitate the practical application of inverted planar heterojunction PVSCs.     

Enhanced performance in inverted polymer solar cells via solution process: Morphology controlling of PEDOT:PSS as anode buffer layer by adding surfactants

Inverted polymer solar cells were fabricated by adding the amphiphilic surfactant ‘Surfynol 104 series’ to Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a anode buffer layer by solution process. With the introduction of Surfynol 104 series-added PEDOT:PSS, it was able to form a homogeneous film by adjusting the wettability of a hydrophobic poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) film. With decrease in series resistance (R_S) and increase in shunt resistance (R_SH), as a result, the short circuit current density (J_SC), open circuit voltage (V_OC) and fill factor (FF) of the optimized device were 10.2 mA/cm², 0.63 V and 61.3%, respectively, calculated the power conversion efficiency (PCE) was 4.0%. In addition, the air stability of the fabricated device was improved.     

Solution‐Processed Nickel Oxide Hole Transport Layers in High Efficiency Polymer Photovoltaic Cells

The detailed characterization of solution‐derived nickel (II) oxide (NiO) hole‐transporting layer (HTL) films and their application in high efficiency organic photovoltaic (OPV) cells is reported. The NiO precursor solution is examined in situ to determine the chemical species present. Coordination complexes of monoethanolamine (MEA) with Ni in ethanol thermally decompose to form non‐stoichiometric NiO. Specifically, the [Ni(MEA)₂(OAc)]⁺ ion is found to be the most prevalent species in the precursor solution. The defect‐induced Ni³⁺ ion, which is present in non‐stoichiometric NiO and signifies the p‐type conduction of NiO, as well as the dipolar nickel oxyhydroxide (NiOOH) species are confirmed using X‐ray photoelectron spectroscopy. Bulk heterojunction (BHJ) solar cells with a polymer/fullerene photoactive layer blend composed of poly‐dithienogermole‐thienopyrrolodione (pDTG‐TPD) and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC₇₁BM) are fabricated using these solution‐processed NiO films. The resulting devices show an average power conversion efficiency (PCE) of 7.8%, which is a 15% improvement over devices utilizing a poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL. The enhancement is due to the optical resonance in the solar cell and the hydrophobicity of NiO, which promotes a more homogeneous donor/acceptor morphology in the active layer at the NiO/BHJ interface. Finally, devices incorporating NiO as a HTL are more stable in air than devices using PEDOT:PSS.     

A Self-Assembled Vertical-Gradient and Well-Dispersed MXene Structure for Flexible Large-Area Perovskite Modules

Advancing hole transport layers (HTL) to realize large-area, flexible, and high-performance perovskite solar cells (PSCs) is one of the most challenging issues for its commercialization. Here, a self-assembled gradient Ti₃C₂T_x MXene incorporated PEDOT:PSS HTL is demonstrated to achieve high-performance large-area PSCs by establishing half-caramelization-based glucose-induced MXene redistribution. Through this process, the Ti₃C₂T_x MXene nanosheets are spontaneously dispersed and redistributed at the top region of HTL to form the unique gradient distribution structure composed of MXene:Glucose:PEDOT:PSS (MG-PEDOT). These results show that the MG-PEDOT HTL not only offers favorable energy level alignment and efficient charge extraction, but also improves the film quality of perovskite layer featuring enlarged grain size, lower trap density, and longer carrier lifetime. Consequently, the power conversion efficiency (PCE) of the flexible device based on MG-PEDOT HTL is increased by 36% compared to that of pristine PEDOT:PSS HTL. Meanwhile, the flexible perovskite solar minimodule (15 cm² area) using MG-PEDOT HTL achieve a PCE of 17.06%. The encapsulated modules show remarkable long-term storage stability at 85 °C in ambient air (≈90% efficiency retention after 1200 h) and enhanced operational lifetime (≈90% efficiency retention after 200 h). This new approach shows a promising future of the self-assembled HTLs for developing optoelectronic devices.     

Layer by layer characterisation of the degradation process in PCDTBT:PC71BM based normal architecture polymer solar cells

This work demonstrates the stability and degradation of OSCs based on poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′ benzothiadiazole)] (PCDTBT): (6,6)-Phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) photoactive blend layers as a function of ageing time in air. Analysis of the stability and degradation process for the OSCs was conducted under ambient air by using current-voltage (I-V) measurements and x-ray photoelectron spectroscopy (XPS). The interface between photoactive layer and HTL (PEDOT:PSS) was also investigated. Device stability was investigated by calculating decay in power conversion efficiency (PCE) as a function of ageing time in the air. The PCE of devices decrease from 5.17 to 3.61% in one week of fabrication, which is attributed to indium and oxygen migration into the PEDOT:PSS and PCDTBT:PC₇₁BM layer. Further, after aging for 1000 h, XPS spectra confirm the significant diffusion of oxygen into the HTL and photoactive layer which increased from 3.0 and 23.3% to 20.4 and 35.7% in photoactive layer and HTL, respectively. Similarly, the indium content reached to 17.9% on PEDOT:PSS surface and 0.4% on PCDTBT:PC₇₁BM surface in 1000 h. Core-level spectra of active layer indicate the oxidation of carbon atoms in the fullerene cage, oxidation of nitrogen present in the polymer matrix and formation of In₂O₃ due to indium diffusion. We also observed a steady fall in the optical absorption of the active layer during ageing in ambient air and it reduced to 76.5% of initial value in 1000 h. On the basis of these experimental results, we discussed key parameters that account for the degradation process and stability of OSCs in order to improve the device performance.     

Efficient Polymer Solar Cells Based on Poly(3‐hexylthiophene):Indene‐C70 Bisadduct with a MoO3 Buffer Layer

Polymer solar cells (PSCs) with poly(3‐hexylthiophene) (P3HT) as a donor, an indene‐C₇₀ bisadduct (IC₇₀BA) as an acceptor, a layer of indium tin oxide modified by MoO₃ as a positive electrode, and Ca/Al as a negative electrode are presented. The photovoltaic performance of the PSCs was optimized by controlling spin‐coating time (solvent annealing time) and thermal annealing, and the effect of the spin‐coating times on absorption spectra, X‐ray diffraction patterns, and transmission electron microscopy images of P3HT/IC₇₀BA blend films were systematically investigated. Optimized PSCs were obtained from P3HT/IC₇₀BA (1:1, w/w), which exhibited a high power conversion efficiency of 6.68%. The excellent performance of the PSCs is attributed to the higher crystallinity of P3HT and better a donor–acceptor interpenetrating network of the active layer prepared under the optimized conditions. In addition, PSCs with a poly(3,4‐ethylenedioxy‐thiophene):poly(styrenesulfonate) (PEDOT:PSS) buffer layer under the same optimized conditions showed a PCE of 6.20%. The results indicate that the MoO₃ buffer layer in the PSCs based on P3HT/IC₇₀BA is superior to that of the PEDOT:PSS buffer layer, not only showing a higher device stability but also resulting in a better photovoltaic performance of the PSCs.     

Stable organic photovoltaic with PEDOT:PSS and MoOX mixture anode interfacial layer without encapsulation

Herein, we report about an efficient and stable organic photovoltaic that uses a poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) and molybdenum oxide (MoO_X) mixture for the anode interfacial layer, and that can reach 4.43% power conversion efficiency (PCE) under AM1.5 conditions. Utilizing PEDOT:PSS:MoO_X (1:1), the shelf lifetime of poly(3-hexylthiophene) (P3HT), and indene-C₆₀ bisadduct (ICBA)-based solar cells without encapsulation, can be realized with only a 25% deterioration after 672 h of storage in air. Furthermore, we compare the photovoltaic performance of the P3HT:ICBA-based organic photovoltaic with PEDOT:PSS, and PEDOT:PSS:MoO_X, in which PEDOT:PSS:MoO_X has outperformed the others. In addition, the water vapor transmission rate of PEDOT:PSS:MoO_X is 0.17 gm/(m² day), which is much less than that of PEDOT:PSS.     

High efficiency bulk heterojunction organic solar cell by using high conductivity modified PEDOT: PSS as a buffer layer

In this paper,bulk heterojunction solar cells with poly-(3-hexylthiophene)(P3HT):[6,6]-phenyl-C61-butyric-acid-methylester(PCBM) as an active layer and modified poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) as a buffer layer are fabricated.The buffer layer is modified by adding 1% to 5% dimethyl sulfoxide(DMSO) into PEDOT:PSS solution before spin-coating.The conductivity of modified PEDOT:PSS and the performance of solar cells with modified PEDOT:PSS are measured.The highest conductivity of modified PEDOT:PSS with 4% DMSO can achieve 89.693 S/cm.The performance of organic solar cell with PEDOT:PSS modified by 4% DMSO is the best.The 4% DMSOmodified-PEDOT:PSS cell has a power conversion efficiency of 3.34%,V oc of 5.7 V,J sc of 14.56 mA/cm 2 and filling factor(FF) of 40.34%.     

Stable Inverted Polymer/Fullerene Solar Cells Using a Cationic Polythiophene Modified PEDOT:PSS Cathodic Interface

A cationic and water‐soluble polythiophene [poly[3‐(6‐pyridiniumylhexyl)thiophene bromide] (P3PHT⁺Br^?)] is synthesized and used in combination with anionic poly(3,4‐ethylenedioxythiophene):poly(p‐styrenesulfonate) (PEDOT:PSS)^? to produce hybrid coatings on indium tin oxide (ITO). Two coating strategies are established: i) electrostatic layer‐by‐layer assembly with colloidal suspensions of (PEDOT:PSS)^?, and ii) modification of an electrochemically prepared (PEDOT:PSS)^? film on ITO. The coatings are found to modify the work function of ITO such that it could act as a cathode in inverted 2,5‐diyl‐poly(3‐hexylthiophene) (P3HT)/[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) polymer photovoltaic cells. The interfacial modifier created from the layer‐by‐layer assembly route is used to produce efficient inverted organic photovoltaic devices (power conversion efficiency ～2%) with significant long‐term stability in excess of 500 h.     

Defect‐Minimized PEDOT:PSS/Planar‐Si Solar Cell with Very High Efficiency

Hybrid solar cells made of a p‐type conducting polymer, poly(3,4‐ethyl thiophene):polystyrenesulfonate (PEDOT:PSS), on Si have gained considerable interest in the fabrication of cost‐effective high‐efficiency devices. However, most of the high power conversion efficiency (PCE) performances have been obtained from solar cells fabricated on surface‐structured Si substrates. High‐performance planar single‐junction solar cells have considerable advantages in terms of processing and cost, because they do not require the complex surface texturing processes. The interface of single‐junction solar cells can critically influence the performance. Here, we demonstrate the effect of adding different surfactants in a co‐solvent‐optimized PEDOT:PSS polymer, which, in addition to acting as a p‐layer and as an anti‐reflective coating, also enhances the device performance of a hybrid planar‐Si solar cell. Using time‐of‐flight secondary ion mass spectrometry, we conduct three‐dimensional chemical imaging of the interface, which enables us to characterize the micropore defects found to limit the PCE. Upon minimizing these micropore defects with the addition of optimized amounts of fluorosurfactant and co‐solvent, we achieve a PEDOT:PSS/planar‐Si cell with a record high PCE of 13.3% for the first time. Our present approach of micropore defect reduction can also be used to improve the performance of other organic electronic devices based on PEDOT:PSS.     

Tuning Hole Transport Layer Using Urea for High‐Performance Perovskite Solar Cells

Interface engineering is critical to the development of highly efficient perovskite solar cells. Here, urea treatment of hole transport layer (e.g., poly(3,4‐ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS)) is reported to effectively tune its morphology, conductivity, and work function for improving the efficiency and stability of inverted MAPbI₃ perovskite solar cells (PSCs). This treatment has significantly increased MAPbI₃ photovoltaic performance to 18.8% for the urea treated PEDOT:PSS PSCs from 14.4% for pristine PEDOT:PSS devices. The use of urea controls phase separation between PEDOT and PSS segments, leading to the formation of a unique fiber‐shaped PEDOT:PSS film morphology with well‐organized charge transport pathways for improved conductivity from 0.2 S cm^?1 for pristine PEDOT:PSS to 12.75 S cm^?1 for 5 wt% urea treated PEDOT:PSS. The urea‐treatment also addresses a general challenge associated with the acidic nature of PEDOT:PSS, leading to a much improved ambient stability of PSCs. In addition, the device hysteresis is significantly minimized by optimizing the urea content in the treatment.     

Influence of aluminium electrode preparation on PCE values of polymeric solar cells based on P3HT and PCBM

The main goal of the paper was investigation of influence of aluminum electrode preparation via thermal evaporation (TE) and the magnetron sputtering (MS) on power conversion efficiency (PCE) of polymeric solar cells. The photovoltaic properties of such three kinds devices based on poly(3-hexylthiophene-2,5-diyl) (P3HT) as ITO/P3HT/Al, ITO/P3HT:PCBM (1:1, w/w)/Al and ITO/PEDOT:PSS/P3HT:PCBM (1:1, w/w)/Al were investigated. For the constructed devices impedance spectroscopy were analyzed. For devices lack of PEDOT:PSS layer or lack of PCBM, photovoltaic parameters were very low and similar to the parameters obtained for device with Al electrode prepared by magnetron sputtering. The devices comprising PEDOT:PSS with P3HT:PCBM showed the best photovoltaic parameters such as a V_OC of 0.60 V, J_SC of 4.61 mA/cm², FF of 0.21, and PCE of 5.7 × 10^?1%.     

Saturated and Multi‐Colored Electroluminescence from Quantum Dots Based Light Emitting Electrochemical Cells

Novel light emitting electrochemical cells (LECs) are fabricated using CdSe‐CdS (core‐shell) quantum dots (QDs) of tuned size and emission blended with polyvinylcarbazole (PVK) and the ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIM‐PF₆). The performances of cells constructed using sequential device layers of indium tin oxide (ITO), poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS), the QD/PVK/IL active layer, and Al are evaluated. Only color saturated electroluminescence from the QDs is observed, without any other emissions from the polymer host or the electrolyte. Blue, green, and red QD‐LECs are prepared. The maximum brightness (≈1000 cd m^‐2) and current efficiency (1.9 cd A^‐1) are comparable to polymer LECs and multilayer QD‐LEDs. White‐light QD‐LECs with Commission Internationale d'Eclairage (CIE) coordinates (0.33, 0.33) are prepared by tuning the mass ratio of R:G:B QDs in the active layer and voltage applied. Transparent QD‐LECs fabricated using transparent silver nanowire (AgNW) composites as the cathode yield an average transmittance greater than 88% over the visible range. Flexible devices are demonstrated by replacing the glass substrates with polyethylene terephthalate (PET).     

Aging process of PEDOT:PSS dispersion and robust recovery of aged PEDOT:PSS as a hole transport layer for organic solar cells

Conducting p-type polymer of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has been widely used for organic optoelectronics, particularly as a hole transport layer for organic solar cells. While the aged PEDOT:PSS dispersion impacts device performance, the aging of PEDOT:PSS dispersion have not been well investigated. Moreover, the recovery process of aged (two-year-old) PEDOT:PSS dispersion has not been demonstrated yet. Herein, it is found that aqueous PEDOT:PSS dispersion undergoes extensive phase separation during the aging process, resulting in both nanoscale and macroscale hydrophobic PEDOT-rich agglomerates. When the aged PEDOT:PSS thin film is integrated into P3HT:PCBM organic solar cells, the PEDOT-rich agglomerates trap the photogenerated holes at the PEDOT:PSS/P3HT interface, resulting in poor extraction efficiency in organic solar cells. To recover a hole transport functionality from aged PEDOT:PSS, three different solvents such as isopropyl alcohol (C₃H₇OH), ethanol (C₂H₅OH) and methanol (CH₃OH) are investigated. Among them, it is found that isopropyl alcohol (IPA) yielded very uniform PEDOT:PSS thin film layer. This is because hydrophobic functional groups of IPA solvent facilitated the preferential solvation of phase separated hydrophobic PEDOT-rich agglomerates. However, when non-optimal concentration of IPA solvents was added into the aged PEDOT:PSS dispersion, the size of PEDOT-rich agglomerates was adversely enlarged. When organic solar cells were fabricated using more than a two-year-old PEDOT:PSS that was treated with IPA solvent, the resulting device performance of organic solar cells was fully recovered and became comparable or better than that of organic solar cells fabricated with fresh PEDOT:PSS.     

Effects of tetramethylene sulfone solvent additives on conductivity of PEDOT:PSS film and performance of polymer photovoltaic cells

A solvent additive in PEDOT:PSS solution is one of many methods to improve the conductivity of the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films. We explore a new type of the solvent additive, namely tetramethylene sulfone (TMS), for the fabrication of the PEDOT:PSS conductive layer in the ITO/PEDOT:PSS/P3HT:PCBM/TiO_x/Al polymer photovoltaic cells, in comparison to a more common dimethyl sulfoxide (DMSO) solvent additive. At optimal conditions, the TMS additive at 10 wt.% has been found to enhance the conductivity of pristine PEDOT:PSS films from 0.04 S/cm up to approximately 189 S/cm, compared with the highest conductivity for the case of the DMSO additive at 15 wt.% of 117 S/cm. Possible mechanisms of this conductivity enhancement, relating to the polymer conformation and the film morphology, have been investigated by Raman spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy. The performance of the polymer photovoltaic cells fabricated with the solvent additives PEDOT:PSS films follows a similar trend to the conductivity of the films as a function of the additive concentration. The additives mainly lead to greater short circuit current density (J_sc) of the photovoltaic cells. The highest power conversion efficiency (PCE) of 2.24% of the device has been obtained with the 10 wt.% TMS additive of, compared to the PCE of 1.48% for the standard device without solvent additive.     

An Organic Hole Transport Layer Enhances the Performance of Colloidal PbSe Quantum Dot Photovoltaic Devices

A thin poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hole transport layer enhances the AM1.5 power conversion efficiency of a PbSe quantum dot (QD)–containing photovoltaic device to 2.4%, from 1.5% for a standard PbSe QD device, a relative increase of 60%. Synchrotron X‐ray reflectivity measurements reveal that the roughness of the interfaces between the various layers decreases dramatically in the presence of the PEDOT:PSS layer. In addition, the device life time under continuous simulated AM1.5 irradiation (100 mW cm^?2), measured in terms of the time required to reach 80% of the normalized efficiency, for the PbSe QD device incorporating the PEDOT:PSS hole transport layer is six times longer than that of the standard PbSe QD device.     

Mitigating Detrimental Effect of Self-Doping Near the Anode in Highly Efficient Organic Solar Cells

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) has been one of the most established hole transport layers (HTL) in organic solar cells (OSCs) for several decades. However, the presence of PSS⁻ ions is known to deteriorate device performance via a number of mechanisms including diffusion to the HTL-active layer interface and unwanted local chemical reactions. In this study, it is shown that PSS⁻ ions can also result in local p-doping in the high efficiency donor:non-fullerene acceptor blends – resulting in photocurrent loss. To address these issues, a facile and effective approach is reported to improve the OSC performance through a two-component hole transport layer (HTL) consisting of a self-assembled monolayer of 2PACz ([2-(9H-Carbazol-9-yl)ethyl]phosphonic acid) and PEDOT:PSS. The power conversion efficiency (PCE) of 17.1% using devices with PEDOT:PSS HTL improved to 17.7% when the PEDOT:PSS/2PACz two-component HTL is used. The improved performance is attributed to the overlaid 2PACz layer preventing the formation of an intermixed p-doped PSS⁻ ion rich region (≈5–10 nm) at the bulk heterojunction-HTL contact interface, resulting in decreased recombination losses and improved stability. Moreover, the 2PACz monolayer is also found to reduce electrical shunts that ultimately yield improved performance in large area devices with PCE enhanced from 12.3% to 13.3% in 1 cm² cells.