Humidity‐Tolerant Roll‐to‐Roll Fabrication of Perovskite Solar Cells via Polymer‐Additive‐Assisted Hot Slot Die Deposition

Heating‐assisted deposition is an industry‐friendly scalable deposition method. This manufacturing method is employed together with slot die coating to fabricate perovskite solar cells via a roll‐to‐roll process. The feasibility of the method is demonstrated after initial testing on a rigid substrate using a benchtop slot die coater in air. The fabricated solar cells exhibit power conversion efficiencies (PCEs) up to 14.7%. A nonelectroactive polymer additive is used with the perovskite formulation and found to improve its humidity tolerance significantly. These deposition parameters are also used in the roll‐to‐roll setup. The perovskite layer and other solution‐processed layers are slot die‐coated, and the fabricated device shows PCEs up to 11.7%, which is the highest efficiency obtained from a fully roll‐to‐roll processed perovskite solar cell to date.     

A Versatile Self‐Organization Printing Method for Simplified Tandem Organic Photovoltaics

Despite recent dramatic enhancements in power conversion efficiencies (PCEs) resulting in values over 10%, the manufacturing of tandem organic solar cells (OSCs) via current printing technologies is subject to tremendous challenges. Existing complicated tandem structures consisting of six or more component layers have been a major obstacle that significantly increases the complexity of printing processes and substantially sacrifices the PCE for printed devices. Here, an innovative printing method is reported that simplifies the fabrication process of the tandem OSCs. By developing a new printing technique using a nanocomposites containing interfacial and photoactive materials, a simultaneously printed bilayer of consisting of interfacial and photoactive layers, achieved through vertical self‐organization, is successfully demonstrated, resulting in tandem OSCs with only four printed layers. Moreover, by rigorously controlling the molecular weight of the interfacial materials, the self‐assembly characteristics are improved and an efficient tandem OSC is yielded with a PCE of 9.1% achieved in printed layers.     

Roll‐to‐Roll Printed Silver Nanowire Semitransparent Electrodes for Fully Ambient Solution‐Processed Tandem Polymer Solar Cells

Silver nanowires (AgNWs) and zinc oxide (ZnO) are deposited on flexible substrates using fast roll‐to‐roll (R2R) processing. The AgNW film on polyethylene terephthalate (PET) shows >80% uniform optical transmission in the range of 550–900 nm. This electrode is compared to the previously reported and currently widely produced indium‐tin‐oxide (ITO) replacement comprising polyethylene terephthalate (PET)|silver grid|poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)|ZnO known as Flextrode. The AgNW/ZnO electrode shows higher transmission than Flextrode above 490 nm in the electromagnetic spectrum reaching up to 40% increased transmission at 750 nm in comparison to Flextrode. The functionality of AgNW electrodes is demonstrated in single and tandem polymer solar cells and compared with parallel devices on traditional Flextrode. All layers, apart from the semitransparent electrodes which are large‐scale R2R produced, are fabricated in ambient conditions on a laboratory roll‐coater using printing and coating methods which are directly transferrable to large‐scale R2R processing upon availability of materials. In a single cell structure, Flextrode is preferable with active layers based on poly‐3‐hexylthiophene(P3HT):phenyl‐C61‐butyric acid methylester (PCBM) and donor polymers of similar absorption characteristics while AgNW/ZnO electrodes are more compatible with low band gap polymer‐based single cells. In tandem devices, AgNW/ZnO is more preferable resulting in up to 80% improvement in PCE compared to parallel devices on Flextrode.     

High Performance Roll‐to‐Roll Produced Fullerene‐Free Organic Photovoltaic Devices via Temperature‐Controlled Slot Die Coating

Solution‐processed organic photovoltaics (OPVs) have continued to show their potential as a low‐cost power generation technology; however, there has been a significant gap between device efficiencies fabricated with lab‐scale techniques—i.e., spin coating—and scalable deposition methods. Herein, temperature‐controlled slot die deposition is developed for the photoactive layer of OPVs. The influence of solution and substrate temperatures on photoactive films and their effects on power conversion efficiency (PCE) in slot die coated OPVs using a 3D printer‐based slot die coater are studied on the basis of device performance, molecular structure, film morphology, and carrier transport behavior. These studies clearly demonstrate that both substrate and solution temperatures during slot die coating can influence device performance, and the combination of hot substrate (120 °C) and hot solution (90 °C) conditions result in mechanically robust films with PCE values up to 10.0% using this scalable deposition method in air. The efficiency is close to that of state‐of‐the‐art devices fabricated by spin coating. The deposition condition is translated to roll‐to‐roll processing without further modification and results in flexible OPVs with PCE values above 7%. The results underscore the promising potential of temperature‐controlled slot die coating for roll‐to‐roll manufacturing of high performance OPVs.     

Elimination of Drying-Dependent Component Deviation Using a Composite Solvent Strategy Enables High-Performance Inkjet-Printed Organic Solar Cells with Efficiency Approaching 16%

Inkjet printing (IJP) is a roll-to-roll (R2R) compatible fabrication method for large-area organic solar cells (OSCs). Unlike the coating process, the films are formed through droplet leveling and merging during IJP, and the pre-deposited droplets are partly dissolved by the subsequent droplets. Such a process yields undesired printing pattern lines, especially in large-area printed films. This study reveals that such a temperature-dependent “drying lines-related” phase separation morphology has caused component variation in the organic blend films, which leads to an obvious inhomogeneity of photocurrent in the printed OSCs. Such a phenomenon is attributed to the solubility difference between organic donor and acceptor molecules in the main printing solvent. A composite solvent strategy of ortho-dichlorobenzene (oDCB)/trimethylbenzene (TMB) and tetralin (THN) is developed to solve this problem. The introduction of THN suppresses the formation of printing drying lines during high-temperature printing due to the preferential miscibility of acceptor in THN, leading to the efficiency improvement to 13.96% and 15.78% for the binary and ternary devices. In addition, the 1 cm² device with a disruptive pattern gives an efficiency of 12.80% and a certificated efficiency of 12.18%.     

Solution‐Processable Perovskite Solar Cells toward Commercialization: Progress and Challenges

In the last few years, organometal halide perovskites (OHPs) have emerged as a promising candidate for photovoltaic (PV) applications. A certified efficiency as high as 23.7% has been achieved, which is comparable with most of the well‐established PV technologies. Their good solubility due to the ionic nature enables versatile low‐temperature solution processes, including blade coating, slot‐die coating, etc., most of which are scalable and compatible with roll‐to‐roll large‐scale manufacturing processes. The low cost, high efficiency, and facile processable features make perovskite solar cells (PSCs) a very competitive PV technology. Despite the great progress, long‐term durability concerns, toxicity issues of both materials and manufacturing process, and lack of robust high‐throughput production technology for fabricating efficient large‐area modules are major obstacles toward commercialization. In this review, the recent progress of commercially available process of PSCs is surveyed, the underlying determinants for upscaling high‐quality PSCs from hydrodynamic characteristics and crystallization thermodynamic mechanism are identified, the influence of external stress factors on stability of PSCs and intrinsic instability mechanism in OHPs themselves is revealed, and the environmental impact and sustainable development of PSC technology are analyzed. Strategies and opportunities for large‐scale production of PSCs are suggested to promote the development of PSCs toward commercialization.     

Self‐Assembled Quasi‐3D Nanocomposite: A Novel p‐Type Hole Transport Layer for High Performance Inverted Organic Solar Cells

Hole transport layer (HTL) plays a critical role for achieving high performance solution‐processed optoelectronics including organic electronics. For organic solar cells (OSCs), the inverted structure has been widely adopted to achieve prolonged stability. However, there are limited studies of p‐type effective HTL on top of the organic active layer (hereafter named as top HTL) for inverted OSCs. Currently, p‐type top HTLs are mainly 2D materials, which have an intrinsic vertical conduction limitation and are too thin to function as practical HTL for large area optoelectronic applications. In the present study, a novel self‐assembled quasi‐3D nanocomposite is demonstrated as a p‐type top HTL. Remarkably, the novel HTL achieves ≈15 times enhanced conductivity and ≈16 times extended thickness compared to the 2D counterpart. By applying this novel HTL in inverted OSCs covering fullerene and non‐fullerene systems, device performance is significantly improved. The champion power conversion efficiency reaches 12.13%, which is the highest reported performance of solution processed HTL based inverted OSCs. Furthermore, the stability of OSCs is dramatically enhanced compared with conventional devices. The work contributes to not only evolving the highly stable and large scale OSCs for practical applications but also diversifying the strategies to improve device performance.     

Development of back‐junction back‐contact silicon solar cells based on industrial processes

We have presented simplified industrial processes to fabricate high performance back‐junction back‐contact (BJBC) silicon solar cells. Good optical surface structures (solar averaged reflectance 2.5%) and high implied open‐circuit voltage (0.695 V) have been realized in the BJBC cell precursors through wet chemical processing, co‐diffusion, P ion implantation and annealing oxidation, as well as laser patterning and plasma enhanced chemical vapour deposition passivation processes. We have achieved a certified high efficiency of close to 22% on BJBC silicon solar cells with the size of 4.04 cm² by using screen printing and co‐firing technologies. The manufacturing process flow further successfully yields efficiency of around 21% BJBC silicon solar cells with enlarged sizes of 6 × 6 cm². The present work has demonstrated that the commercialization of low‐cost and high‐efficiency BJBC solar cells is possible because we have used processes compatible with existing production lines. Copyright © 2017 John Wiley & Sons, Ltd.     

Hole‐Transporting Materials Incorporating Carbazole into Spiro‐Core for Highly Efficient Perovskite Solar Cells

Hole‐transporting materials (HTMs) play a significant role in hole transport and extraction for perovskite solar cells (PeSCs). As an important type of HTMs, the spiro‐architecture‐based material is widely used as small organic HTM in PeSCs with good photovoltaic performances. The skeletal modification of spiro‐based HTMs is a critical way of modifying energy level and hole mobility. Thus, many spiro alternatives are developed to optimize the spiro‐type HTMs. Herein, a novel carbazole‐based single‐spiro‐HTM named SCZF‐5 is designed and prepared for efficient PeSCs. In addition, another single‐spiro HTM SAF‐5 with reported 10‐phenyl‐10H‐spiro[acridine‐9,9′‐fluorene] (SAF) core is also synthesized for comparison. Through varying from SAF core to SCZF core as well as comparing with the classic 9,9′‐spiro‐bifluorene, it is found that the new HTM SCZF‐5 exhibits more impressive power conversion efficiency (PCE) of 20.10% than SAF‐5 (13.93%) and the commercial HTM spiro‐OMeTAD (19.11%). On the other hand, the SCZF‐5‐based device also has better durability in lifetime testing, indicating the newly designed SCZF by integrating carbazole into the spiro concept has good potential for developing effective HTMs.     

All Solution‐Processed Chalcogenide Solar Cells – from Single Functional Layers Towards a 13.8% Efficient CIGS Device

Solution processing of inorganic thin films has become an important thrust in material research community because it offers low‐cost and high‐throughput deposition of various functional coatings and devices. Especially inorganic thin film solar cells – macroelectronic devices that rely on consecutive deposition of layers on large‐area rigid and flexible substrates – could benefit from solution approaches in order to realize their low‐cost nature. This article critically reviews existing deposition approaches of functional layers for chalcogenide solar cells with an extension to other thin film technologies. Only true solutions of readily available metal salts in appropriate solvents are considered without the need of pre‐fabricated nanoparticles. By combining three promising approaches, an air‐stable Cu(In,Ga)Se₂ thin film solar cell with efficiency of 13.8% is demonstrated where all constituent layers (except the metal back contact) are processed from solutions. Notably, water is employed as the solvent in all steps, highlighting the potential for safe manufacturing with high utilization rates.     

Roll‐to‐roll gravure printing of organic photovoltaic modules—insulation of processing defects by an interfacial layer

Gravure printing as direct patterning roll‐to‐roll (R2R) production technology can revolutionize the design of thin‐film organic photovoltaic (OPV) devices by allowing feasible manufacturing of arbitrary‐shaped modules. This makes a distinction to coating methods, such as slot die coating, in which the pattern is limited to continuous stripes. Here, we analyze the thin‐film formation and its influence on OPV module performance as the gravure printing of hole transport and photoactive layers are transferred from laboratory to R2R pilot production environment. Insertion of a 0.8‐nm layer of lithium fluoride (LiF) as an interfacial layer between the active layer and the electron contact provided insulation against the detrimental pinholes formed in the R2R printing process. Using this device configuration, we produced well‐performing R2R‐printed monolithic modules with a mean efficiency of 1.7%. In comparison, reference modules with an efficiency of 2.2% were fabricated using laboratory‐scale bench top sheet‐level process. Surface energy and tension measurements together with optical microscopy were used to analyze the printability of the materials. The pinhole insulation was investigated in detail by processing R2R‐printed OPV modules with different interfacial layer materials and performing electrical measurements under dark and AM1.5 illumination conditions. Furthermore, we analyzed the LiF distribution using X‐ray photoelectron spectroscopy. The insulating nature of the LiF layer to improve module performance was confirmed by manufacturing lithographically artificial pinholes in device structures. The results show the possibility to loosen the production environment constraints and the feasibility of fabricating well‐performing thin‐film devices by R2R gravure printing. Copyright © 2014 John Wiley & Sons, Ltd.     

Synergistic Roll‐to‐Roll Transfer and Doping of CVD‐Graphene Using Parylene for Ambient‐Stable and Ultra‐Lightweight Photovoltaics

A roll‐to‐roll (R2R) transfer technique is employed to improve the electrical properties of transferred graphene on flexible substrates using parylene as an interfacial layer. A layer of parylene is deposited on graphene/copper (Cu) foils grown by chemical vapor deposition and are laminated onto ethylene vinyl acetate (EVA)/poly(ethylene terephthalate). Then, the samples are delaminated from the Cu using an electrochemical transfer process, resulting in flexible and conductive substrates with sheet resistances of below 300 Ω sq^?1, which is significantly better (fourfold) than the sample transferred by R2R without parylene (1200 Ω sq^?1). The characterization results indicate that parylene C and D dope graphene due to the presence of chlorine atoms in their structure, resulting in higher carrier density and thus lower sheet resistance. Density functional theory calculations reveal that the binding energy between parylene and graphene is stronger than that of EVA and graphene, which may lead to less tear in graphene during the R2R transfer. Finally, organic solar cells are fabricated on the ultrathin and flexible parylene/graphene substrates and an ultra‐lightweight device is achieved with a power conversion efficiency of 5.86%. Additionally, the device shows a high power per weight of 6.46 W g^?1 with superior air stability.     

Fluorinated Polymer Yields High Organic Solar Cell Performance for a Wide Range of Morphologies

Device performance is recognized to be generally sensitive to morphology in bulk heterojunction solar cells. Through the use of quantitative morphological measurements, it is demonstrated that devices based on benzodithiophene and fluorinated benzotriazole moieties constitute an exception to this design rule and exhibit a range of morphologies that yield similar high performance. In particular, the fill factor (FF) remains above 65% even with factor of two changes in domain size and factor of two changes in relative domain purity. Devices with active layer thicknesses of 250 nm are employed, which are capable of increasing optical absorption to produce high photocurrent. The general insensitivity to both morphology and thickness is likely related to the measured low equilibrium miscibility of fullerene in the polymer of 3‐4%. The materials and processes investigated therefore provide insights into functional material design that yield increased processing latitude and may be more amenable to roll‐to‐roll processing.     

An Effective Method for Recovering Nonradiative Recombination Loss in Scalable Organic Solar Cells

Regarded as a critical step in commercial applications, scalable printing technology has become a research frontier in the field of organic solar cells. However, inevitable efficiency loss always occurs in the lab‐to‐manufacturing translation due to the different fabrication processes. In fact, the decline of photovoltaic performance is mainly related to voltage loss, which is mainly affected by the diversity of phase separation morphology and the chemical structures of photoactive materials. Fullerene derivative indene‐C₆₀ bisadduct (ICBA) is introduced into a PBDB‐T‐2F:IT‐4F system to control the active layer morphology during blade‐coating process. Accordingly, as a symmetrical fullerene derivative, ICBA can regulate the crystallization tendency and molecular packing orientation and suppress charge carrier recombination. This ternary strategy overcomes the morphology issues caused by weaker shear impulse in blade‐coating process. Benefiting from the reduced nonradiative recombination loss, 1.05 cm² devices are fabricated by blade coating with a power conversion efficiency of 13.70%. This approach provides an effective support for recovering the voltage loss during scalable printing approaches.     

Ternary organic solar cells based on non-fullerene acceptors: A review

Organic solar cells (OSCs) have reached their second golden age in recent two years with a boosted number of publications. Non-fullerene acceptor (NFA) materials have become a rising star in the field which are widely applied in organic solar cells because of their excellent optoelectronic properties, such as strong light-harvesting ability and tunable energy level. Unlike the low synthetic flexibility and high production cost of fullerene materials, NFAs exhibit flexible structures, and relatively low fabrication costs. Recently, the ternary strategy has become another hot research topic in the field, which introduces a third component into the binary host system for OSCs. The application of a ternary strategy can break the limits of light absorption brought by the host system, improve the morphology and energy level alignment for the active layer and thus improved the efficiency of organic solar cell devices. Benefiting from the advancement in both NFA and ternary strategy, the power conversion efficiency (PCE) of organic solar cell has exceeded over 17.5% to date. A comprehensive review of the recent progress in NFA based ternary OSCs (TOSCs) is needed in the field. Herein, this review mainly focuses on recent research on ternary organic solar cells using NFA materials during the last two years. Firstly, device physics and frequently used active materials in NFA based TOSCs are summarized and discussed. Then, the recent reported high-performance NFA based TOSCs are reviewed. Finally, the outlook and future research direction in the field are proposed. This review aims to provide an insight into NFA based TOSCs and help researchers to explore the full potential of OSCs.     

Gold(III) Corroles for High Performance Organic Solar Cells

While the use of molecular materials having long‐lived triplet excited state(s) for harvesting solar energy could be an effective approach to boost up the power conversion efficiency (PCE) of organic solar cells (OSCs), the performances of this kind of OSCs as reported in the literature are low (< 2.9% PCE attained for the vacuum‐deposited OSCs). Herein is described the realization of high performance OSCs by using gold(III) 5,10,15‐triphenylcorrole ( Au‐C1 ), gold(III) 10‐(p‐trifluoromethylphenyl)‐5,15‐diphenylcorrole ( Au‐C2 ), and gold(III) 10‐(pentafluorophenyl)‐5,15‐diphenyl‐corrole ( Au‐C3 ), as electron‐donors. These gold(III) corroles display excited state lifetimes of ≥ 25 μs and low emission quantum yields of < 0.15%. With the complexes Au‐C1 , Au‐C2 , and Au‐C3 , vacuum‐deposited OSCs, which give PCEs of 2.7%, 3.0%, and 1.8%, respectively, are fabricated. The PCE can be further boosted up to 4.0% after thermal treatment of the OSC devices. Meanwhile, a solution‐processed OSC based on Au‐C2 with a high PCE of 6.0% is fabricated. These PCE values are among the best reported for both types of vacuum‐deposited and solution‐processed OSCs fabricated with metal‐organic complexes having long‐lived excited states as electron‐donor material. The underlying mechanism for the inferior performance of the reported OSCs is discussed.     

Printable and Large‐Area Organic Solar Cells Enabled by a Ternary Pseudo‐Planar Heterojunction Strategy

Bulk heterojunction (BHJ) processing technology has had an irreplaceable role in the development of organic solar cells (OSCs) in the past decades due to the significant advantages in achieving high‐power conversion efficiency (PCE). However, the difficulty in exploring and regulating morphology makes it inadequate for upscaling large‐area OSCs. In this work, printable high‐performance ternary devices are fabricated by a pseudo‐planar heterojunction (PPHJ) strategy. The fullerene derivative indene‐C₆₀ bisadduct (ICBA) is incorporated into PM6/IT‐4F system to expand the vertical phase separation and facilitate an obvious PPHJ structure. After the addition of ICBA, the IT‐4F enriches on the surface of active layer, while PM6 is accumulated underneath. Furthermore, it increases the crystallinity of PM6, which facilitates exciton dissociation and charge transfer. Accordingly, 1.05 cm² devices are fabricated by blade‐coating with an enhanced PCE of 14.25% as compared to the BHJ devices (13.73%). The ternary PPHJ strategy provides an effective way to optimize the vertical phase separation of organic semiconductor during scalable printing methods.     

Boundary condition model for the simulation of organic solar cells

Organic solar cells (OSCs) are promising photovoltaic devices to convert solar energy into electrical energy. Their many advantages such as lightweight, flexibility and low manufacturing costs are intrinsic to the organic/polymeric technology. However, because the performance of OSCs is still not competitive with inorganic solar cells, there is urgent need to improve the device performance using better designs, technologies and models. In this work, we focus on developing an accurate physics-based model that relates the charge carrier density at the metal-organic boundaries to the current density in OSCs. This analysis is based on our previous studies on single-carrier and bipolar diodes. The model for the boundary condition of the charge carrier density at the interfaces of OSCs follows a power-law function with the current density, both in dark and under illumination. Simulated current-voltage characteristics are verified with experimental results. The numerical simulations of the current-voltage characteristics of OSCs consider well-established models for the main physical and optical processes that take place in the device: light absorption and generation of excitons, dissociation of excitons into free charge carriers, charge transport, recombination and injection-extraction of free carriers. Our analysis provides important insights on the influence of the metal-organic interfaces on the overall performance of OSCs. The model is also used to explain the anomalous S-shape current-voltage curves found in some experimental data.     

Back‐contact solar cells: a review

Ever since the first publications by R.J. Schwartz in 1975, research into back‐contact cells as an alternative to cells with a front and rear contact has remained a research topic. In the last decade, interest in back‐contact cells has been growing and a gradual introduction to industrial applications is emerging. The goal of this review is to present a comprehensive summary of results obtained throughout the years. Back‐contact cells are divided into three main classes: back‐junction (BJ), emitter wrap‐through (EWT) and metallisation wrap‐through (MWT), each introduced as logical descendents from conventional solar cells. This deviation from the chronology of the developments is maintained during the discussion of technological results. In addition to progress on manufacturing these cells, aspects of cell modelling and module manufacturing are discussed and an outlook towards industrial implementation is presented. Copyright © 2005 John Wiley & Sons, Ltd.     

19% efficient n‐type Czochralski silicon solar cells with screen‐printed aluminium‐alloyed rear emitter

High and stable lifetimes recently reported for n‐type silicon materials are an important and promising prerequisite for innovative solar cells. To exploit the advantages of the excellent electrical properties of n‐type Si wafers for manufacturing simple and industrially feasible high‐efficiency solar cells, we focus on back junction n⁺np⁺ solar cells featuring an easy‐to‐fabricate full‐area screen‐printed aluminium‐alloyed rear p⁺ emitter. Independently confirmed record‐high efficiencies have been achieved on n‐type phosphorus‐doped Czochralski‐grown silicon material: 18·9% for laboratory‐type n⁺np⁺ solar cells (4 cm²) with shadow‐mask evaporated front contact grid and 17·0% for front and rear screen‐printed industrial‐type cells (100 cm²). The electrical cell parameters were found to be perfectly stable under illumination. Copyright © 2006 John Wiley & Sons, Ltd.