Chen Weijie

Efficient large-area flexible solar cells and modules are demonstrated based on a printable, transparent, low-surface-roughness, flexible electrode (silver nanowires:zinc-chelated polyethylenimine). A power conversion efficiency of 13.2% is obtained for a 54 cm² solar module. The flexible electrode is also demonstrated in high-performance flexible quantum-dot light-emitting diodes.

Abstract

Development of large-area flexible organic solar cells (OSCs) is highly desirable for their practical applications. However, the efficiency of the large-area flexible OSCs severely lags behind small-area devices. Here, efficient large-area flexible single cells with power conversion efficiency (PCE) of 13.1% and 12.6% for areas of 6 and 10 cm², and flexible modules with a PCE of 13.2% (54 cm²) based on poly(ethylene terephthalate)/Ag grid/silver nanowires (AgNWs):zinc-chelated polyethylenimine (PEI-Zn) composite electrodes are reported. The solution-processed flexible transparent electrode of AgNWs:PEI-Zn shows low surface roughness and good optoelectronic and mechanical properties. PEI-Zn is conductive and optically transparent. It can adhere to and wrap the AgNWs under electrostatic interaction between the negatively charged surface (AgNWs) and positively charged protonated amine groups (in PEI-Zn). It wraps the AgNWs networks and fills the void space to achieve a smooth surface. The flexible electrode is validated in both flexible OSCs and flexible quantum-dots light-emitting diodes (QLEDs). Small-area flexible OSCs show a PCE of 16.1%, and flexible QLEDs show an external quantum efficiency of 13.3%. In the end, a flexible module is demonstrated to charge a mobile phone as a flexible power source (shown in Video S1, Supporting Information).

Publication date: 18 August 2021

Source: Joule, Volume 5, Issue 8

Author(s): Ayan A. Zhumekenov, Makhsud I. Saidaminov, Omar F. Mohammed, Osman M. Bakr

Two regular terpolymers are used as the effective dopant-free hole transport materials for inverted perovskite solar cells. The power conversion efficiency of solar cells can reach up to 18.17%, with negligible hysteresis and good ambient stability, which is mainly due to the well-matched energy level, improved film morphology, low carrier recombination, and higher hole extraction efficiency of the perovskite layer.

In inverted perovskite solar cells (PSCs), hole transport materials (HTMs) can efficiently improve hole extraction and transfer as well as the crystallization of perovskite films and thus enhance the photovoltaic performance. Herein, two dopant-free, regular A₁–D–A₂–D-type (D: electron donor; A: electron acceptor) polymeric HTMs, PTPDTBT and PDPPTBT, are developed by integrating the benzothiadiazole unit (A₁) with the electron-accepting species of either a thieno[3,4-c]pyrrole-4,6-dione or a pyrrolo[3,4-c]pyrrole-1,4-dione segment (A₂), respectively, where the thiophene unit (D) results in a kinked molecular geometry. These A₁–D–A₂–D-type terpolymers exhibit comparable nonpolar properties but distinct film-quality morphology and charge transport characteristics. PDPPTBT with the more insulating side-chain groups is found to improve the quality of perovskite films cast on top with larger grain sizes and more homogeneous crystallization. As a consequence, the PDPPTBT-based PSCs without any dopants and additional interlayers display a champion power conversion efficiency of 18.17%, one of the highest values of MAPbI₃-based inverted PSCs using dopant-free D-A-type polymeric HTMs. Furthermore, the PDPPTBT-based device exhibits negligible hysteresis and high long-term stability. This work provides a potential strategy to design dopant-free A₁–D–A₂–D-type polymeric HTMs for efficient and stable PSCs.

Polyaniline@black phosphorous based nanocomposite with excellent structural stability represent a promising electrode material to develop a flexible supercapacitor device. This device is integrated as a portable power source in a smartwatch and pressure sensor that track human health parameters via wireless communication.

Abstract

Flexible energy storage devices are becoming significantly important to power wearable and portable devices that monitor physiological parameters for many biomedical applications. Many hybrid nanomaterials based on 2D materials are used in order to improve the performance of flexible energy storage devices. Here, a hybrid nanocomposite is synthesized through in situ polymerization of aniline in the presence of black phosphorus (BP) nanoflakes. This nanocomposite, polyaniline (PANI)@BP, is employed to fabricate flexible supercapacitor (FSC) electrodes. PANI@BP FSCs can provide a power source for biometric devices. The generated signal can be transmitted to a smartphone in real time via wireless communication. Such a compact and lightweight integrated device has been used to track a human heart beat while powered by PANI@BP FSC. These findings are providing a promising example of a flexible energy storage device that can be integrated with different real-time health monitoring devices.

Flexible single-component organic solar cells with an excellent efficiency of 7.21% were fabricated for the first time. Simultaneously, they exhibited better mechanical durability (>95% retention after 1000 bending cycles) and storage stability (97.6% retention after 430 h) in the nitrogen atmosphere compared to BHJ-type flexible devices.

Abstract

Owing to the advantages of being lightweight and compatible with surfaces with different deformations, flexible organic solar cells (OSCs) have broad scopes of applications, including wearable electronics and portable devices. Most flexible OSCs focus on the two-component bulk-heterojunction (BHJ) photo-active layers, but they usually suffer from degradation problems both in efficiency and mechanical durability derived from the limited phase stability under mechanical and thermal stress. Whereas, single-component organic solar cells (SCOSCs) based on the double-cable conjugated polymer are supposed to possess excellent mechanical robustness and long-term stability. Here, the first flexible SCOSCs based on a double-cable polymer are fabricated on a transparent silver nanowires (AgNWs) electrode on a plastic foil. Impressively, the obtained flexible SCOSCs exhibited a power conversion efficiency (PCE) of 7.21%. The flexible SCOSCs are further demonstrated to possess superior mechanical robustness (>95% retention after 1000 bending cycles) and storage stability (>97% retention after 430 h in nitrogen atmosphere) compared to several BHJ-type flexible OSCs. The pseudo-free-standing tensile test and morphology investigation are conducted to reveal the distinction in mechanical durability of the single-component polymer film and the BHJ-type films. Besides, ultraflexible SCOSCs are also fabricated, indicating the application prospect and superiority in flexible devices and wearable electronic products.

Dopant engineering for spiro-OMeTAD hole-transporting materials towards efficient perovskite solar cells. The presence of M(TFSI) _n salts as p-type dopants are required to improve the hole transfer of spiro-OMeTAD, critical for photovoltaic performance. This study assesses the role of metal cations in the process, revealing the superiority of Zn-based dopants as compared to redox-active Cu-based ones and others as producing a very high fill factor of close to 80% a V _OC of 1.15 V and a power conversion efficiency of 21.9%.

Abstract

One of the most prominent hole-transporting material (HTM) for hybrid perovskite solar cells has been 2,2″,7,7″-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD), which is commonly doped with metal bis(trifluoromethylsulfonyl)imide (M(TFSI) _n ) salts that contribute to generating the active radical cation HTM species. The underlying role of the metal cation, however, remains elusive. Here, the effect of metal cations (M = Li, Zn, Ca, Cu, and Sc) on doping spiro-OMeTAD is analyzed by a combination of techniques, including electron paramagnetic resonance spectroscopy and cyclic voltammetry, which is complemented by photovoltaic device and hole mobility analysis. As a result, the authors reveal the superiority of Zn(TFSI)₂ salts in device performances as compared to the others, including redox-active Cu(TFSI)₂. This analysis thereby unravels new design principles for dopant engineering in HTMs for hybrid perovskite photovoltaics.

Hot-casting is demonstrated to boost the performance of halogen-free solvents processed organic solar cells (OSCs), achieving power conversion efficiency higher than that of the halogen solvents processed counterparts, and is effective in both binary and ternary OSCs.

Abstract

Despite the substantial climb of the power conversion efficiency (PCE) of organic solar cells (OSCs), the majority of processing solvent remains halogenated and stand as a critical issue for commercialization. Herein, a halogen-free solvent system consisting of toluene (Tol) and 1-phenylnaphthalene (PN) is used to replace the traditional halogenated chloroform (CF) and1-chloronaphthalene (CN) for the processing of the PM6:M36 OSC, reducing the maximum PCE from 15.0% to 13.3%. Hot-casting is demonstrated to boost the maximum PCE of halogen-free solvents processed OSCs back to 15.2%. The preheated substrate fastens the evaporation of Tol and enables similar film-forming kinetics to CF, resulting in the inhibition of immoderate molecular aggregation and excessive phase separation. Ternary OSCs, with either another donor or acceptor as the third component, can further improve device PCE to 15.8%, confirming the versatile photovoltaic systems that this hot-casting method can be applied to. Encouragingly, the hot-casting processed binary and ternary OSCs also exhibit retained storage stability. Therefore, hot-casting is demonstrated as a superior strategy to fabricate OSCs without efficiency and stability loss using halogen-free solvents.

A novel hole-transport material (HTM) with the ability to bind to perovskites via halogen bonding is synthesized. Thanks to this interaction, the HTM molecules form a homogenous and ordered layer, improving the perovskite/HTM interface. This results in enhanced open circuit voltage and stability, showing the advantages of using halo-functional HTMs in perovskite solar cells.

Abstract

Interfaces play a crucial role in determining perovskite solar cells, (PSCs) performance and stability. It is therefore of great importance to constantly work toward improving their design. This study shows the advantages of using a hole-transport material (HTM) that can anchor to the perovskite surface through halogen bonding (XB). A halo-functional HTM (PFI) is compared to a reference HTM (PF), identical in optoelectronic properties and chemical structure but lacking the ability to form XB. The interaction between PFI and perovskite is supported by simulations and experiments. XB allows the HTM to create an ordered and homogenous layer on the perovskite surface, thus improving the perovskite/HTM interface and its energy level alignment. Thanks to the compact and ordered interface, PFI displays increased resistance to solvent exposure compared to its not-interacting counterpart. Moreover, PFI devices show suppressed nonradiative recombination and reduced hysteresis, with a V _oc enhancement of ≥20 mV and a remarkable stability, retaining more than 90% efficiency after 550 h of continuous maximum-power-point tracking. This work highlights the potential that XB can bring to the context of PSCs, paving the way for a new halo-functional design strategy for charge-transport layers, which tackles the challenges of charge transport and interface improvement simultaneously.

By fine-tuning the optical field distribution and employing photovoltaic materials with low energy losses in tandem photovoltaic cell, a power conversion efficiency of 19.64% is achieved.

Abstract

Despite more potential in realizing higher photovoltaic performance, the highest power conversion efficiency (PCE) of tandem organic photovoltaic (OPV) cells still lags behind that of state-of-the-art single-junction cells. In this work, highly efficient double-junction tandem OPV cells are fabricated by optimizing the photoactive layers with low voltage losses and developing an effective method to tune optical field distribution. The tandem OPV cells studied are structured as indium tin oxide (ITO)/ZnO/bottom photoactive layer/interconnecting layer (ICL)/top photoactive layer/MoO _x /Ag, where the bottom and top photoactive layers are based on blends of PBDB-TF:ITCC and PBDB-TF:BTP-eC11, respectively, and ICL refers to interconnecting layer structured as MoO _x /Ag/ZnO:PFN-Br. As these results indicate that there is not much room for optimizing the bottom photoactive layer, more effort is put into fine-tuning the top photoactive layer. By rationally modulating the composition and thickness of PBDB-TF:BTP-eC11 blend films, the 300 nm-thick PBDB-TF:BTP-eC11 film with 1:2 D/A ratio is found to be an ideal photoactive layer for the top sub-cell in terms of photovoltaic characteristics and light distribution control. For the optimized tandem cell, a PCE of 19.64% is realized, which is the highest result in the OPV field and certified as 19.50% by the National Institute of Metrology.

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Kyungeun Jung, Kwonwoo Oh, Du Hyeon Kim, Jae Won Choi, Ki Chul Kim, Man-Jong Lee

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Yongrui Yang, Fanyi Min, Yali Qiao, Zheng Li, Florian Vogelbacher, Zhaoxin Liu, Wenkun Lv, Yang Wang, Yanlin Song

Interfacial layers consisting of organic molecules with a permanent dipole moment exhibit enhanced charge carrier selectivity in silicon solar cells. However, thermal annealing has a detrimental effect on it due to the decomposition of the dipole materials which is investigated by in more detail by device simulations. Furthermore, degradation under ambient conditions is observed, limiting the potential of the dipole material.

Interfacial layers consisting of organic molecules with a permanent dipole moment exhibit enhanced charge carrier selectivity when applied as electron-selective contacts in crystalline silicon (c-Si) heterojunction solar cells. It is found that thermal annealing has a detrimental effect on the charge carrier selectivity of dipole materials based on the amino acid l-histidine mixed with a fluorosurfactant. Although, the implied open-circuit voltage (iV _oc) increases with annealing, the V _oc decreases significantly which is accompanied by a decrease in the built-in voltage (V _bi) and increase in the specific contact resistivity (ρ _c). Based on numerical device simulations, it is concluded that the tunneling of electrons through the dipole layer becomes less effective with increasing annealing temperature due to the decomposition of the dipole materials. The decomposition leads to a more “resistive” interfacial layer and to a gradient in the electron quasi-Fermi potential and, thus, a decrease in V _oc. Furthermore, storage under ambient air at room temperature degraded the electron-selective contacts substantially, limiting the potential of the dipole material for the application in silicon organic heterojunction solar cells.

Herein, Cl atoms are introduced into the BDT-based thienyl side chains and BDD-based thienyl π-bridges to obtain two chlorinated polymer donors H1 and H2, respectively. Systematically comparing the photovoltaic properties of H1 and H2 demonstrates that the device performance of polymer donors is sensitive to the position of the chlorine atoms.

Introducing substituent groups has been regarded as an effective method to construct highly efficient polymer donors. However, the correlation between the position of substituent groups and the device performance of polymer donors has rarely been carefully studied and compared. Herein, Cl atoms are introduced into the BDT-based thienyl side chains and BDD-based thienyl π-bridges to obtain two chlorinated donor−acceptor (D−A) polymer donors H1 and H2, respectively. By systematically comparing the photovoltaic properties of H1 and H2, it is found that the device performance of polymer donors is sensitive to the position of chlorine atoms. The nonfullerene organic solar cells (OSCs) based on H1:IT-4F and H1:Y6 display a superior power conversion efficiency (PCE) of 12.34 and 15.62%, whereas the PCE of H2:IT-4F and H2:Y6 is 11.04 and 13.80%. As the H1-based blend shows more desirable aggregation morphology, more preferential face-on orientation, and more efficient extraction dissociation occurs. The current work demonstrates that the position of chlorine substitution can be reasonably optimized for state-of-the-art polymer donors in the highly efficient nonfullerene OSCs.

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Mohammad Ismail Hossain, Md. Shahiduzzaman, Safayet Ahmed, Md. Rashedul Huqe, Wayesh Qarony, Ahmed Mortuza Saleque, Md. Akhtaruzzaman, Dietmar Knipp, Yuen Hong Tsang, Tetsuya Taima, Juan Antonio Zapien

Herein, p-type blue carbon dots (B-CDs) are applied as an interface passivation layer to enhance efficiency and stability of CsPbI₂Br solar cells. B-CDs can passivate perovskite through hydrogen and coordinative bonds, form a P–N junction with the n-type perovskite to enhance charge transfer, and increase film hydrophobicity. The CsPbI₂Br devices with B-CDs modification show an efficiency of 16.76%.

Abstract

Interface modification to minimize charge recombination and trapping for efficient charge transport is crucial for the performance of perovskite solar cells (PSCs). Herein, functionalized p-type blue carbon dots (B-CDs) are ventured as an interface passivation layer to enhance the efficiency and long-term stability of all-inorganic CsPbI₂Br PSCs. It is found that first the blue carbon dots with abundant NH, CN, CO, and CO functional groups effectively passivate defects by reacting with I⁻ and Pb²⁺ ions in the perovskite through hydrogen and coordinative bonds. Second, the p-type B-CDs modifiers form a P–N junction with the n-type perovskite to provide efficient pathways for hole transfer and electron blocking. Third, the B-CDs increase the hydrophobicity of the perovskite film to improve the stability of CsPbI₂Br PSCs. With the above advantages, the CsPbI₂Br PSC with B-CDs modification shows an efficiency as high as 16.76%, one of the highest for its type. In addition, the modification renders significant improvement of air and light stability, with 95.33% of the initial PCE retained after storage in the ambient environment for 1000 h. This work demonstrates the great potential of B-CDs application in perovskite-based optoelectronic devices.

A regioregular narrow-bandgap n-type polymer, L15, is synthesized, showing higher electron mobility and larger absorption coefficient compared to its random analog. When applied as an electron acceptor in all-polymer solar cells (all-PSCs), L15 yields outstanding efficiencies of 15.2% and 16.2% in binary and ternary all-PSCs, respectively.

Abstract

Narrow-bandgap n-type polymers with high electron mobility are urgently demanded for the development of all-polymer solar cells (all-PSCs). Here, two regioregular narrow-bandgap polymer acceptors, L15 and MBTI, with two electron-deficient segments are synthesized by copolymerizing two dibrominated fused-ring electron acceptors (FREA) with distannylated aromatic imide, respectively. Taking full advantage of the FREA and the imide, both polymer acceptors show narrow bandgap and high electron mobility. Benefiting from the more extended absorption, better backbone ordering, and higher electron mobility than those of its regiorandom analog, the L15-based all-PSC yields a high power conversion efficiency (PCE) of 15.2% when blended with the polymer donor PM6. More importantly, MBTI incorporating a benzothiophene-core FREA segment shows relatively higher frontier molecular orbital levels than L15, forming a cascade-like energy level alignment with L15 and PM6. Based on this, ternary all-PSCs are designed where MBTI is introduced as a guest into the PM6:L15 host system. Thanks to further optimal blend morphology and more balanced charge transport, the PCE is improved up to 16.2%, which is among the highest values for all-PSCs. The results demonstrate that combining an FREA and an aromatic imide to construct regioregular narrow-bandgap polymer acceptors provides an effective approach to fabricate highly efficient all-PSCs.

1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) is introduced via an antisolvent engineering to regulate the growth of perovskite film. Upon the incorporation of TPBi, the perovskite film obtains a higher crystallinity and enhanced hole blocking capability on the surface. The TPBi-incorporated perovskite solar cell delivers a high efficiency of 21.79% and keeps ≈92% of the initial value after 1000 h in the ambient atmosphere.

Abstract

With potential commercial applications, inverted perovskite solar cells (PSCs) have received wide-spread attentions as they are compatible with tandem devices and processed at low-temperature. Nevertheless, their efficiencies remain unsatisfactory due to insufficient film quality on hydrophobic hole transport layer and limited hole-blocking capability of the electron transport layer. Herein, 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), an n-type semiconductor, is incorporated into the antisolvent to simultaneously regulate the grain growth and charge transport of perovskite films. TPBi facilitates the crystallization of perovskites along (100) orientation. Besides, TPBi is mainly distributed near the top surface of perovskite film and enhances the hole-blocking capability of the area adjacent to the surface. The superior properties of this film lead to a remarkable improvement in the open-circuit voltage of inverted PSCs. The champion device achieves a high power conversion efficiency of 21.79% while keeping ≈92% of its initial value after 1000 h storage in the ambient atmosphere. This work provides an effective way to evidently promote the performance of inverted PSCs and illustrates its underlaying mechanism.

The intrinsic mechanisms of doping effects on improving or decreasing the efficiency of organic–inorganic hybrid perovskite (OIHP) solar cells are qualitatively and quantitatively clarified. The influences of the doping concentration, defects, trap density, and carrier mobility on the parameters (J _SC, V _OC, fill factor, and power conversion efficiency) of OIHP solar cells are identified by means of spectroscopic investigations.

Abstract

To enhance the efficiency and stability of the organic–inorganic hybrid perovskite (OIHP) solar cells, doping has been demonstrated as a straightforward method. Nevertheless, the perception of trap states regulated by doping and their effects on the performance of solar cells is not in-depth. Herein, typical OIHPs (CH₃NH₃PbI₃ and Cs_0.05FA_0.85MA_0.10Pb(I_0.97Br_0.03)₃) doped with RbI are employed to expound the doping mechanism in affecting the efficiency of devices. Systematic spectroscopic characterizations indicate that doping significantly influences the photocarrier dynamics via directly regulating the trap states. The results indicate that doping would reduce the trap density by passivating defects and induce extra trapping centers. This directly manipulates the transient transport of the photocarriers and finally influences the output of devices. The optimization of solar cell performance requires the tradeoff of competitive relation between the passivation and introduction of trapping centers. The results provide the spectroscopic perception on how doping concentration affects trap density, carrier dynamics, transport behavior, and ultimately the parameters of devices. It provides a straightforward guidance to the design and optimization of OIHP-based solar cells.

Nature Photonics, Published online: 02 August 2021; doi:10.1038/s41566-021-00847-2

Even without defect passivation, the surface recombination of perovskite solar cells can be suppressed by reducing the concentration of minority carriers at the front surface. By introducing a wide-gap perovskite, CsPbBr₃ nanocrystals, to the front surface, the inverted MAPbI₃ cells can achieve significant enhancement of open-circuit voltages without losing photocurrent.

A bandgap gradient at the front surface of solar absorbers can effectively suppress surface recombination while not affecting photocurrent. Herein, it is demonstrated that a front-surface gradient can be formed in an inverted perovskite cell by introducing perovskite quantum dots (QDs) between the hole-transporting layer (HTL) and the remaining absorber. Ultraviolet photoelectron spectroscopy reveals that, with the addition of CsPbBr₃ QDs onto the HTL substrate, the subsequently deposited MAPbI₃ is converted from mild p-type to n-type, and the resultant band alignment can effectively reduce the electron concentration at the front surface without significantly affecting hole extraction. Multiple independent characterizations further confirm the reduction of surface recombination. As a result, the inverted MAPbI₃ cells exhibit an open-circuit voltage of 1.154 V, which translates to a nonradiative recombination loss of 0.15 V and a power conversion efficiency of 20.51%.