Chen Weijie

Publication date: 21 August 2019

Source: Joule, Volume 3, Issue 8

Author(s): Xiuqiang Li, George Ni, Thomas Cooper, Ning Xu, Jinlei Li, Lin Zhou, Xiaozhen Hu, Bin Zhu, Pengcheng Yao, Jia Zhu

Publication date: 18 September 2019

Source: Joule, Volume 3, Issue 9

Author(s): Minjin Kim, Gi-Hwan Kim, Tae Kyung Lee, In Woo Choi, Hye Won Choi, Yimhyun Jo, Yung Jin Yoon, Jae Won Kim, Jiyun Lee, Daihong Huh, Heon Lee, Sang Kyu Kwak, Jin Young Kim, Dong Suk Kim

Context & Scale

Summary

Graphical Abstract

A bifunctional dye molecule, 5,15‐bis(2,6‐dioctoxyphenyl)‐10‐(bis(4‐hexylphenyl)‐amino‐20‐4‐carboxyphenylethynyl)porphyrinato]zinc(II) (YD₂‐o‐C8), is introduced into CsPbI₂Br PSCs. It not only broadens the light absorption range of the perovskite but also reduces the energy loss (E _loss) by interface passivation. As a result, the efficiency markedly enhances from 7.02% to 10.13%, featuring a short‐circuit current (J _SC) of 12.05 mA cm⁻² and a record‐high open‐circuit voltage (V _OC) of 1.37 V.

Inorganic lead halide perovskites are attracting increasing attention due to their much better thermal stability than the organic–inorganic hybrid perovskite materials. Thus, the low power conversion efficiency (PCE) is a key issue for the inorganic lead halide perovskite solar cells (PSCs). This is mainly due to their wider bandgap and larger energy loss (E _loss) in the devices. Herein, for solving this issue, a dye molecule‐assisted engineering using the dye of 5,15‐bis(2,6‐dioctoxyphenyl)‐10‐(bis(4‐hexylphenyl)‐amino‐20‐4‐carboxyphenylethynyl)porphyrinato]zinc(II) (YD₂‐o‐C8) is demonstrated. Results indicate that this molecule has a bifunctional effect, not only as a co‐sensitization layer for CsPbIBr₂ with broader absorption spectrum but also reduces the E _loss by interface passivation. Specifically, the light absorption range of the photoactive layer is broadened from 600 to nearly 680 nm. At the same time, the interfacial charge recombination is highly reduced. After optimizing, the champion PCE is enhanced from 7.02% to 10.13%, and record‐high open‐circuit voltage (V _OC) of 1.37 V and short‐circuit currents (J _SC) of 12.05 mA cm⁻² are achieved. This study opens a simple and efficient way to improve the efficiency of inorganic PSCs.

Crystalline quality of perovskite films is improved due to the additional nucleation sites provided by carbon quantum dots (CQDs) and the interaction of the pyrrolic N in ligands of CQDs with CH₃NH₃PbI₃ (MAPI). This technique opens up a promising pathway to improve the photovoltaic performance of low‐temperature paintable carbon‐electrode‐based perovskite solar cells (LC‐PSCs) and potentially also of other thin‐film solar cells.

Low‐temperature paintable carbon‐electrode‐based perovskite solar cells (LC‐PSCs) are developed predominantly due to several significant advantages of carbon electrodes: they do not require a hole transport layer (HTL) and are low‐cost, easy to fabricate on a large scale, and possess high ambient stability. The most critical hindrance to the photovoltaic performance of LC‐PSCs is the inferior contact between the perovskite and carbon layers. Herein, carbon quantum dots (CQDs) as interface modifiers between the perovskite layer and carbon electrode are applied, which can facilitate hole injection into the carbon electrode, thus improving the photovoltaic performance of LC‐PSCs. Meanwhile, the crystalline properties and hole mobility of the perovskite layer are improved significantly, and defect states in the perovskite layer are passivated following the embedding of CQDs. Finally, a champion efficiency of 13.3% in LC‐PSCs based on perovskite‐CQDs hybrid films without HTL is achieved for an active area of 1 cm², which represents a 24.3% improvement over the pristine device. Furthermore, LC‐PSC devices maintain more than 95% of their initial efficiency under demanding conditions (humidity >40%, 1000 h). This work opens up a promising pathway to improve the photovoltaic performance of LC‐PSCs and potentially also of other thin‐film solar cells.

Diketopyrrolopyrrole (DPP)‐based polymers have gained significant research interest in the organic electronics community. In this work, a combination of a DPP polymer derivative, PBDTT‐DPP, is used, blending with IEICO‐4F, a state‐of‐the‐art small‐molecule acceptor, yielding a champion power conversion efficiency of 9.66%, among the best performance of DPP‐based solar cells.

Abstract

The high crystallinity and ability to harvest near‐infrared photons make diketopyrrolopyrrole (DPP)‐based polymers one of the most promising donors for high performing organic solar cells (OSCs). However, DPP‐based OSC devices still suffer from the trade‐off between energetic loss (E _loss) and maximum external quantum efficiency (EQE_max), which significantly hinders their potential. Thus far, the replacement of fullerenes with small molecule acceptors did not wisdom the performance development of DPP‐donor‐based solar cells due to severe charge recombination issues. In this work, efficient DPP‐based solar cells are reported using low bandgap fused ring electron acceptor, IEICO‐4F. PBDTT‐DPP:IEICO‐4F OSC devices deliver a champion power conversion efficiency of 9.66% with successful interface engineering along with low E _loss of 0.57 eV and a high EQE_max (>70%).

Perovskite solar cells (PVSCs) with discrete SnO₂ nanoparticle modification layers are constructed via spin coating the SnO₂ dispersions on poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The discrete SnO₂ nanoparticle film let holes pass and block electrons to diffuse toward PEDOT:PSS, which enhances the extraction efficiency, leading to an increase in a power conversion efficiency of p‐i‐n‐type PVSCs.

Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is the most widely used hole transport materials for perovskite solar cells (PVSCs) with a p‐i‐n structure. However, the solar cells based on PEDOT:PSS show a low photoconversion efficiency due to the poor crystallinity of a perovskite film on it. Besides, the acidity of PEDOT:PSS performance critically influences the long‐term stability of PVSCs. Herein, a layer of the discrete SnO₂ nanoparticle film is deposited on the surface of PEDOT:PSS to modify the surface of the PEDOT:PSS film. This discrete SnO₂ nanoparticle film acts as the buffer layer between the PEDOT:PSS and MAPbI₃, which not only improves the crystallization of the quality of the perovskite film, but also provides a selective‐carrier pathway to enhance the extraction of holes and to block the diffusion of electrons. The SnO₂ modified devices show a power conversion efficiency of 18.04%, with a great improvement compared with the 12.24% efficiency of PEDOT:PSS only devices. This work demonstrates that it is possible to enhance the performance of PVSCs via n‐type nanoparticle modification of hole transport layer and provides a new guidance for PVSCs interface modification engineering.

A versatile alkaline earth metals doping strategy is utilized to engineer the electronic structure of NiO _x contacts for inverted planar perovskite solar cells, which demonstrates a power conversion efficiency of 19.49% with a high open‐circuit voltage of 1.14 V. Enhanced charge extraction and conductivity are responsible for the high‐performance devices.

Organometallic halide perovskite solar cells (PSCs) are rapidly evolving as the promising photovoltaic technologies with high record efficiency over 24%. The inorganic p‐type semiconductor NiO _x is extensively used as important hole transport layers for the realization of stable and hysteresis‐free solar cells due to their good electronic properties, facile fabrication, and excellent chemical endurance. However, the critical issues of NiO _x films including poor intrinsic conductivity and mismatched band alignment limit further improvement of the device performance. Herein, it is demonstrated that a versatile alkaline earth metal (Mg, Ca, Sr, and Ba) doping strategy can effectively engineer the electronic properties of NiO _x contacts in inverted planar PSCs. Alkaline earth metal doping can deepen valence band maximum and enhance the hole conductivity of NiO _x films, which better aligns the energy band in solar cells. The champion device based on Sr‐doped NiO _x films attains a power conversion efficiency of 19.49% with a high open‐circuit voltage (V _OC) of 1.14 V for NiO _x ‐based CH₃NH₃PbI₃ devices. The resulted device shows negligible hysteresis and high stability as well. This finding provides a systematic doping strategy to further improve the performance of inverted planar PSCs.

High‐performance ternary‐blend solar cells are fabricated by incorporating two nonfullerene acceptors. The enhanced power conversion efficiency mainly benefits from the broadened light harvesting and the optimized morphology. This work demonstrates that elaborately selecting a suitable third component with complementary basic properties is critical for the development of high‐performance ternary solar cells.

Abstract

Ternary polymer solar cells (PSCs) are one of the most promising device architectures that maintains the simplicity of single‐junction devices and provides an important platform to better tailor the multiple performance parameters of PSCs. Herein, a ternary PSC system is reported employing a wide bandgap polymeric donor (PBTA‐PS) and two small molecular nonfullerene acceptors (labeled as LA1 and 6TIC). LA1 and 6TIC keep not only well‐matched absorption profiles but also the rational crystallization properties. As a result, the optimal ternary PSC delivers a state of the art power conversion efficiency (PCE) of 14.24%, over 40% higher than the two binary devices, resulting from the prominently increased short‐circuit current density (J _sc) of 22.33 mA cm⁻², moderate open‐circuit voltage (V _oc) of 0.84 V, and a superior fill factor approaching 76%. Notably, the outstanding PCE of the ternary PSC ranks one of the best among the reported ternary solar cells. The greatly improved performance of ternary PSCs mainly derives from combining the complementary properties such as absorption and crystallinity. This work highlights the great importance of the rational design of matched acceptors toward highly efficient ternary PSCs.

Diketopyrrolopyrrole (DPP)‐based polymers have gained significant research interest in the organic electronics community. In this work, a combination of a DPP polymer derivative, PBDTT‐DPP, is used, blending with IEICO‐4F, a state‐of‐the‐art small‐molecule acceptor, yielding a champion power conversion efficiency of 9.66%, among the best performance of DPP‐based solar cells.

Abstract

The high crystallinity and ability to harvest near‐infrared photons make diketopyrrolopyrrole (DPP)‐based polymers one of the most promising donors for high performing organic solar cells (OSCs). However, DPP‐based OSC devices still suffer from the trade‐off between energetic loss (E _loss) and maximum external quantum efficiency (EQE_max), which significantly hinders their potential. Thus far, the replacement of fullerenes with small molecule acceptors did not wisdom the performance development of DPP‐donor‐based solar cells due to severe charge recombination issues. In this work, efficient DPP‐based solar cells are reported using low bandgap fused ring electron acceptor, IEICO‐4F. PBDTT‐DPP:IEICO‐4F OSC devices deliver a champion power conversion efficiency of 9.66% with successful interface engineering along with low E _loss of 0.57 eV and a high EQE_max (>70%).

Highly air‐stable PbSe colloidal quantum dots (CQDs) are produced via an in situ chloride and cadmium passivation technique. A high‐quality film is fabricated using solution‐phase ligand exchange and a one‐step deposition method. By using a PbS‐EDT (EDT = 1,2‐ethanedithiol) hole‐transporting layer, a PbI₂‐capped PbSe‐CQD‐based photovoltaic device shows a record efficiency of 10.68% with impressive air and light soaking stability.

Abstract

Low‐cost solution‐processed lead chalcogenide colloidal quantum dots (CQDs) have garnered great attention in photovoltaic (PV) applications. In particular, lead selenide (PbSe) CQDs are regarded as attractive active absorbers in solar cells due to their high multiple‐exciton generation and large exciton Bohr radius. However, their low air stability and occurrence of traps/defects during film formation restrict their further development. Air‐stable PbSe CQDs are first synthesized through a cation exchange technique, followed by a solution‐phase ligand exchange approach, and finally absorber films are prepared using a one‐step spin‐coating method. The best PV device fabricated using PbSe CQD inks exhibits a reproducible power conversion efficiency of 10.68%, 16% higher than the previous efficiency record (9.2%). Moreover, the device displays remarkably 40‐day storage and 8 h illuminating stability. This novel strategy could provide an alternative route toward the use of PbSe CQDs in low‐cost and high‐performance infrared optoelectronic devices, such as infrared photodetectors and multijunction solar cells.

The small organic molecule (2‐(1,10‐phenanthrolin‐3‐yl)naphth‐6‐yl)diphenylphosphine oxide is explored as cathode interfacial material to reduce the extraction barrier between phenyl‐C61‐butyric acid methyl ester and Ag. With the better contact quality thanks to this molecule, both opaque and semitransparent p‐i‐n perovskite solar cell achieve improved performance and stability.

Abstract

Metal halide perovskite solar cells (PSCs) in the inverted planar p‐i‐n configuration often employ phenyl‐C61‐butyric acid methyl ester (PC₆₁BM) as electron transport layer, onto which Ag is deposited as outer electrode. However, the energy offset between PC₆₁BM and Ag imposes an energy barrier for electron extraction. In this work, to improve the contact quality of this stack, a small organic molecule (2‐(1,10‐phenanthrolin‐3‐yl)naphth‐6‐yl)diphenylphosphine oxide (DPO) as a cathode interfacial material (CIM), inserted between PC₆₁BM and Ag, is introduced. In devices with the indium tin oxide (ITO)/NiO _x /methylammonium lead iodide (MAPbI₃)/PC₆₁BM/CIM/Ag configuration, it is found that this results in fill factor (FF) and short‐circuit current density values (J _SC) that are up to ≈34% and ≈1 mA cm⁻² higher, respectively, compared to DPO‐free devices. Inserting additional thin ZnO nanoparticle layers further improves the contact quality, leading to a power conversion efficiency of 18.2%. Semitransparent PSCs, utilizing DPO as an interlayer buffer layer are also realised. Resultant devices exhibit improved performance compared to DPO‐free devices. This proves that DPO withstands the sputtering of ITO, and may thus find application in perovskite‐based tandem devices. It is concluded that DPO acts as an excellent cathode modifier, opening new device‐engineering opportunities for p‐i‐n PSCs, especially in their semitransparent implementation.

Me₄NBr is introduced to passivate the Sn–Pb based perovskite interface, leading to an improved efficiency of 13.97%, mainly due to the effective reduction of defects. By adopting the poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS)/poly(triarylamine) (PTAA) as the hole transport material (HTM), a Sn‐based perovskite solar cell with an efficiency of 14.56% is obtained. Furthermore, the Me₄NBr treated Sn–Pb perovskite cells also demonstrate a significant stability enhancement.

Abstract

Tin–lead (Sn–Pb) based hybrid perovskite solar cell is investigated as a potential solution to extend the light absorption spectrum range, and to reduce environmental hazard caused by lead in the perovskite materials. Nonetheless, due to the instability of tin, the Sn–Pb based perovskite solar cells suffer from more severe efficiency degradation when compared to the lead‐based perovskite solar cells, which restricts its further development. Here, a quaternary ammonium halide compound, Me₄NBr, is introduced to passivate the Sn–Pb based perovskite surface. The Me₄NBr effectively reduces the surface defects and enhances the open circuit voltage and fill factor of the Sn–Pb based perovskite solar cell. Moreover, the Me₄NBr treated Sn–Pb perovskite cells also demonstrate a significant stability enhancement when compared with the untreated Sn–Pb perovskite cells.

A lead‐bismuth (Pb‐Bi) binary metal based all‐inorganic perovskite film is successfully fabricated and applied as absorber layer to enhance the stability of perovskite solar cells (PSCs). High power conversion efficiency (PCE) of 11.9% is obtained for the all‐inorganic (PSC).The PCE only reduced by 10% under atmospheric humidity of 40% in 4 weeks.

Abstract

A lead‐bismuth (Pb‐Bi) binary metal based all‐inorganic perovskite film is successfully fabricated and applied as absorber layer to enhance the stability of perovskite solar cells (PSCs). Unlike the Pb‐only perovskite‐based device, the Pb‐Bi binary metal perovskite based one shows better tolerance to humidity and oxygen. High power conversion efficiency (PCE) of 11.9% is obtained for the all‐inorganic (PSC). Noticeably, the PCE only reduced by 10% under atmospheric humidity of 40% in four weeks. An electron‐only device also shows reduced trap states. The improved stability and PCE is ascribed to higher quality perovskite film with less trap states and smaller series resistance (R _s) in the device.

An ultrathin, nanogradient, and robust WO _x ‐based flexible solar absorber is developed by combining the self‐doping concept and intrinsically absorptive WO _x film. The total thickness is around 100 nm, which is substantially thinner than all other reported absorbers, but it still possesses super absorptivity, adhesion and bendable nature, and outstanding thermal stability, which is promising for flexible and wearable energy applications.

Advances in flexible and wearable energy‐related devices increase the need for highly efficient, low‐cost, ultrathin solar selective absorber coatings (SSACs). Herein, the fabrication of nanogradient WO _x ‐based SSACs with excellent properties, including a superior solar absorptance of 0.93, an outstanding thermal robustness of up to 300 °C, and substrate independence, is reported. More importantly, the thickness of WO _x ‐based SSACs is only approximately 100 nm, which is substantially thinner than all other reported SSACs. These features arise from the two intrinsically absorptive WO _x layers on a thin nanoplasmonic W layer. The deposition process is based on self‐doped reactive sputtering via limited tungsten oxidation due to a small amount of oxygen. The WO _x ‐based SSACs on a flexible polyimide sheet demonstrate stable performance, strong adhesion, and bendable nature. The proposed self‐doped fabrication process provides a new way to design cost‐effective ultrathin SSACs to meet the demand for large‐scale flexible energy harvesting and supply applications.

The recent progress in double‐metallic lead‐free perovskite materials and devices is comprehensively reviewed. In particular, theory calculation, electronic structure, and fundamental properties of double perovskites are deliberated. The achievements and challenges in their application including solar cells, photon detectors, and laser devices, are summarized. In addition, the viewpoints for future research of this class of perovskites are also provided.

Lead halide perovskite (ABX₃) has attracted considerable attention due to its applicability as absorber layers in highly efficient photovoltaic cells. With regard to the lead toxicity, double‐metallic lead‐free perovskite, A₂B^IB^IIIX₆, in which the neighboring B⁺ and B³⁺ sites in the crystal microstructure are alternately occupied by monovalent‐metal and trivalent‐metal cations, is regarded to be a promising alternative to the widely used lead‐based perovskites. This review aims to summarize the recent advances in the new class of A₂B^IB^IIIX₆ double‐metallic lead‐free perovskites. In particular, the electronic structure, synthesis, property, and their applications in devices, for example, photovoltaics, photodetectors, and light emitting diodes, is carefully classified and presented. Notably, the theoretical calculations point out that there is much room toward potential applications for this new class of perovskite materials. The present review provides a holonomic conclusion and opens new perspectives toward realizing higher performance of A₂B^IB^IIIX₆‐based devices.

Micrometer‐thick stable CsPbBr₃ perovskite films are obtained through a facile vacuum drying process. Green emission with a brightness as high as 200 cd m⁻² is achieved from blue light with a back luminance of 1000 cd m⁻², which decays by only ≈2% when the films are tested after 18 days of exposure to ambient environment.

Abstract

Metal halide perovskite materials have attracted great attention owing to their fascinating optoelectronic characteristics and low cost fabrication via facile solution processing. One of the potential applications of these materials is to employ them as color‐conversion layers (CCLs) for visible blue light to achieve full‐color displays. However, obtaining thick perovskite films to realize complete color conversion is a key challenge. Here, the fabrication of micrometer‐level thick CsPbBr₃ perovskite films is presented through a facile vacuum drying approach. An efficient green photoconversion is realized in a 3.8 µm thick film from blue light @ 463 nm. For a back luminance of 1000 cd m⁻², the brightness of the resulting green emission can reach as high as 200 cd m⁻². Furthermore, only ≈2% of decay in brightness is observed when the films are tested after 18 days of exposure to ambient environment. In addition, a potential design is also proposed for full‐color displays with perovskite materials incorporated as CCLs.

Single‐walled carbon nanotube electrodes in organic solar cells and perovskite solar cells are reviewed from a synthesis and applications point of views. The emerging thin‐film solar cells have the potential to become next‐generation flexible and portable energy devices. Replacement of conventional electrodes by single‐walled carbon nanotubes is crucial in achieving such devices.

Abstract

Emerging solar cells, namely, organic solar cells and perovskite solar cells, are the thin‐film photovoltaics that have light to electricity conversion efficiencies close to that of silicon solar cells while possessing advantages in having additional functionalities, facile‐processability, and low fabrication cost. To maximize these advantages, the electrode components must be replaced by materials that are more flexible and cost‐effective. Researchers around the globe have been looking for the new electrodes that meet these requirements. Among many candidates, single‐walled carbon nanotubes have demonstrated their feasibility as the new alternative to conventional electrodes, such as indium tin oxide and metals. This review discusses various growth methods of single‐walled carbon nanotubes and their electrode applications in thin‐film photovoltaics.

Next‐generation solar cells consisting of organic materials are studied. To develop novel dyes for dye‐sensitized solar cells, the essential dye structures are explored to attain high efficiency. Additionally, the interfaces in the perovskite solar cells are characterized via electrochemical methods, and newly developed laser deposition methods for perovskite layers are discussed.

Abstract

Next‐generation organic solar cells such as dye‐sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are studied at the National Institute of Advanced Industrial Science and Technology (AIST), and their materials, electronic properties, and fabrication processes are investigated. To enhance the performance of DSSCs, the basic structure of an electron donor, π‐electron linker, and electron acceptor, i.e., D–π–A, is suggested. In addition, special organic dyes containing coumarin, carbazole, and triphenylamine electron donor groups are synthesized to find an effective dye structure that avoids charge recombination at electrode surfaces. Meanwhile, PSCs are manufactured using both a coating method and a laser deposition technique. The results of interfacial studies demonstrate that the level of the conduction band edge (CBE) of a compact TiO₂ layer is shifted after TiCl₄ treatment, which strongly affects the solar cell performance. Furthermore, a special laser deposition system is developed for the fabrication of the perovskite layers of PSCs, which facilitates the control over the deposition rate of methyl ammonium iodide used as their precursor.

The incorporation of π‐extended phosphoniumfluorene electrolytes as hole‐blocking layers in planar perovskite solar cells results in a significant enhancement in both the fill factor and the open‐circuit voltage of the devices. The latter can be enhanced by up to 120 mV as compared to the commonly used bathocuproine hole blocking layer.

Abstract

Four π‐extended phosphoniumfluorene electrolytes (π‐PFEs) are introduced as hole‐blocking layers (HBL) in inverted architecture planar perovskite solar cells with the structure of ITO/PEDOT:PSS/MAPbI₃/PCBM/HBL/Ag. The deep‐lying highest occupied molecular orbital energy level of the π‐PFEs effectively blocks holes, decreasing contact recombination. It is demonstrated that the incorporation of π‐PFEs introduces a dipole moment at the PCBM/Ag interface, resulting in significant enhancement of the built‐in potential of the device. This enhancement results in an increase in the open‐circuit voltage of the device by up to 120 mV, when compared to the commonly used bathocuproine HBL. The results are confirmed both experimentally and by numerical simulation. This work demonstrates that interfacial engineering of the transport layer/contact interface by small molecule electrolytes is a promising route to suppress nonradiative recombination in perovskite devices and compensates for a nonideal energetic alignment at the hole‐transport layer/perovskite interface.

Organic‐inorganic hybrid two‐dimensional (2D) perovskites (n≤5) have recently attracted significant attention due to their promising stability and optoelectronic properties. Normally, 2D perovskites contain a mono cation (e.g., methylammonium (MA+) or formamidinium (FA+)). Here, we report for the first time on fabricating 2D perovskites (n=5) with mixed cations of MA+, FA+, and cesium (Cs+). The use of these triple cations leads to the formation of a smooth, compact surface morphology with larger grain size and fewer grain boundaries compared to the conventional MA‐based counterpart. The resulting perovskite also exhibits longer carrier lifetime and higher conductivity in triple‐cation 2D perovskite solar cells (PSCs). The power conversion efficiency (PCE) of 2D PSCs with triple cations was enhanced by more than 80% (from 7.80% to 14.23%) compared to PSCs fabricated with a mono cation; the PCE is also higher than that of PSCs based on binary‐cation (MA+‐FA+ or MA+‐Cs+) 2D structures.

Publication date: 21 August 2019

Source: Joule, Volume 3, Issue 8

Author(s): Jaehoon Chung, Seong Sik Shin, Geunjin Kim, Nam Joong Jeon, Tae-Youl Yang, Jun Hong Noh, Jangwon Seo

Context & Scale

Summary

Graphical Abstract

An aggregation‐breaking strategy to inhibit the trend of self‐aggregation of benzo[1,2‐b:4,5‐b']difuran (BDF)‐based polymers, the power conversion efficiency (PCE, 12.42%) with a high fill factor (FF, 75.19%) is obtained, which is higher than that of PBDTTz‐SBP:ITIC‐based devices. This proposed strategy may be a good choice to surpass the benzo[1,2‐b:4,5‐b']dithiophene (BDT)‐based polymers and obtain the state‐of‐the‐art photovoltaic materials.

Great efforts have been devoted to semiconductive polymers based on the benzo[1,2‐b:4,5‐b’]dithiophene (BDT) unit, and great progress has been achieved in organic solar cells, whereas the analogue core benzo[1,2‐b:4,5‐b’]difuran (BDF) has the similar extended planar structure, and the electronic structure gets less development in the photovoltaic system. Herein, a novel BDF core‐based copolymer PBDFTz‐SBP is synthesized, which decorates with two 2D extended biphenyl side chains and shows a relatively small polymer segments distortion and strong intermolecular π–π interaction in relation to the BDT‐based polymer. Using this polymer, an aggregation‐breaking strategy to suppress the trend of self‐aggregation of polymers’ segment is proposed, which obtains an appropriate phase separation and forms favorable bicontinuous interpenetrating networks for charge transport. It is found that PBDFTz‐SBP:ITIC achieves an excellent power‐conversion efficiency (PCE) of 12.42% with an open‐circuit voltage (V _OC) of 0.89 V, a short‐circuit current density (J _SC) of 18.56 mA cm⁻², and a high fill factor (FF) of 75.19% when the spin‐coating solution is 120 °C, which is higher than that of PBDTTz‐SBP:ITIC‐based devices even under optimized conditions. This proposed strategy may be a good choice for the BDF unit to construct the donor (D)–acceptor (A) type polymers and surpass the counterpart BDT‐based photovoltaic materials and obtain a state‐of‐the‐art PCEs.

A high quality FAPbI₃ ‐based perovskite film is successfully developed via a ligand and additive synergetic process. The planar flexible solar cell based on this film shows a record power conversion efficiency of 19.38%. This device exhibits excellent ambient stability and mechanical stability.

Abstract

Compared with silicon‐based solar cells, organic–inorganic hybrid perovskite solar cells (PSCs) possess a distinct advantage, i.e., its application in the flexible field. However, the efficiency of the flexible device is still lower than that of the rigid one. First, it is found that the dense formamidinium (FA)‐based perovskite film can be obtained with the help of N‐methyl‐2‐pyrrolidone (NMP) via low pressure‐assisted method. In addition, CH₃NH₃Cl (MACl) as the additive can preferentially form MAPbCl_{3− x} I _x perovskite seeds to induce perovskite phase transition and crystal growth. Finally, by using FAI·PbI₂·NMP+x%MACl as the precursor, i.e., ligand and additive synergetic process, a FA‐based perovskite film with a large grain size, high crystallinity, and low trap density is obtained on a flexible substrate under ambient conditions due to the synergetic effect, e.g., MACl can enhance the crystallization of the intermediate phase of FAI·PbI₂·NMP. As a result, a record efficiency of 19.38% in flexible planar PSCs is achieved, and it can retain about 89% of its initial power conversion efficiency (PCE) after 230 days without encapsulation under ambient conditions. The PCE retains 92% of the initial value after 500 bending cycles with a bending radii of 10 mm. The results show a robust way to fabricate highly efficient flexible PSCs.

The recent progress in lead‐free tin (Sn)‐based perovskite solar cells (PSCs) is reviewed. After briefing the structural and optoelectronic properties of Sn‐based perovskites, the film deposition methods and the strategies toward high performance in Sn‐based PSCs are then summarized. The challenges and prospective opportunities in this field are also discussed.

Perovskite solar cells (PSCs) have achieved state‐of‐the‐art efficiency, approaching monocrystalline silicon solar cells due to the superior optoelectronic properties and intensive research efforts, fulfilling its forthcoming commercial use at affordable costs. Nevertheless, the toxicity of lead (Pb) is still one of the obstacles hindering future large‐scale production. Herein, the recent progress of emerging lead‐free tin (Sn)‐based PSCs is reviewed. First, the structural and photovoltaic‐related properties of Sn‐based perovskites are summarized. Following a brief introduction of film deposition methods, strategies recently adopted to obtain high performance are then discussed in detail. Finally, the current challenges and prospective opportunities are provided to help the further progression of Sn‐based PSCs.

Compared with the traditional vacuum vapor deposition method, the sputtering‐deposited electrode has smoother surface, negligible pin‐hole, less material consumption, and can be used in large‐area fabrication. Through the interface modification of Au/Spiro‐OMeTAD, the perovskite solar cells (PSCs) with direct‐current (DC) magnetron sputtering‐deposited gold electrode achieve a high efficiency of 18.32%.

Perovskite solar cells (PSCs) attract great attention due to their low cost and high efficiency. In general, the Au cathode, a key component in PSCs, is prepared via an uneconomic vacuum thermal deposition method. Instead, the sputtering deposition method is much more economic and faster. However, it is generally thought that the organic hole transport layer such as 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (Spiro‐OMeTAD) can be easily damaged by the high energy plasma during the sputtering process. Thus, the performance of the PSCs greatly decreases. Herein, the structure of the planar PSCs is carefully manipulated by matching the thickness of Spiro‐OMeTAD layer and the Au film. With the further engineering of the interface of the Au/Spiro‐OMeTAD, the planar PSCs with the sputtered Au cathode exhibit a highly reproducible average efficiency of 17.6% ± 0.8%, with the best efficiency of 18.3%. In addition, the Cu electrode is demonstrated by the sputtering method. Finally, the Au sputter deposition is scaled up to make a high efficiency (14.7%) 10 × 10 cm² module. This demonstrates well that the sputtering deposition of the metal cathode is an effective way for the fabrication of high efficient PSCs for future industrialization.