Chen Weijie

Asymmetrical acceptor–donor–acceptor conjugated molecule as a versatile buffer for simultaneously enhancing photovoltaic performance and stability is elaborated. The conductive buffer can not only substantially eliminate interfacial defects and suppress detestable non-radiative recombination, but also effectively facilitate charge transfer efficiency at the interface, resulting in an excellent efficiency of 24.81%. What's more, benefiting from the unexceptionable protective effect, greatly improved humidity and thermal stability are delivered.

Abstract

Interface in perovskite solar cells (PSCs) is of vital importance because it dominates deep-level defects and non-radiative recombination, thus impacting both efficiency and stability further. Herein, a symmetrical acceptor–donor–acceptor (A–D–A) conjugated molecule with the core architecture of terthieno[3,2-b hiophene and 2-(3-oxo-2,3-dihydro-1 H-inden-1-ylidene)malononitrile, named 6TIC, as a versatile buffer layer, is adopted to enhance photovoltaic performance and stability simultaneously. It is found that the conjugated molecule filling at grain boundaries and surface can not only chemically anchor with perovskite components to substantially eliminate interfacial defects and suppress detestable non-radiative recombination, but also effectively improve the energy level alignment and facilitate charge transfer efficiency at the interface, resulting in an excellent power conversion efficiency of 24.81% with an admirable fill factor of 84.5%. Furthermore, benefiting from the unexceptionable surface protection effect of the hydrophobic buffer layer, greatly improved operational stability is delivered, with retaining 90% of initial efficiency for 960 h aging in a relative humidity of 60 ± 5% air and 1450 h aging under continuous 85 °C heating stress. This strategy may provide a new avenue for advancing high-efficiency and stable PSCs.

A good double-layered hole transporting layer (HTL) is made by combining a poor SnO HTL and amphiphilic polymer PDTON as a Co-HTL, cross-linker, passivator, and surface modification agent. Tin-perovskite solar module based on the double-layered HTL with an active area of 25.2 cm² achieves the efficiency of 10% is reported for the first time.

Abstract

An exquisite, engineering of two poor hole transporting materials (HTMs, SnO, and PDTON) to form an excellent double-layered HTL (SnO/PDTON) for inverted tin-perovskite solar modules (TPSMs) is developed. SnO/PDTON has better photovoltaic performance than the commonly used PEDOT:PSS HTM when large-area TPSMs are fabricated. Thermally evaporated SnO (that is a simple, available oxide with high hole mobility, good transparency, and adjustable frontier orbitals energy levels) film is used as a main hole transporting layer (HTL). Amphiphilic polymer PDTON (having the amine and ether groups on the side chains) film is used as a Co-HTL, cross-linker, passivator, and interface modification agent, as unveiled various physicochemical studies. Double-layered SnO/PDTON with a flat morphology and good affinity toward perovskite precursor solution creates also a proper surface for depositing large-area, high-quality TPsk film. Therefore, TPSM (25.2 cm² active area on 10 cm × 10 cm ITO substrate) based on double-layered SnO/PDTON HTL achieving an efficiency over 10% with a negligible current hysteresis is reported for the first time. This study emphasizes not only the exquisite design of combining the specific characteristics of two prosaic HTMs to become a good double-layered HTL but also gives a direction toward fabricating TPSMs to be applied in all-perovskite tandem solar module.

Surface passivation using bulky chloride cations helps to increase the open-circuit voltage (V_oc) in semi-transparent bifacial fully bromide FAPbBr₃ perovskite solar cell (PSC) reaching values up to 1.73V. Up-scaling process is demonstrated paves the way for application in building-integrated photovoltaics (BIPV) and internet of thing (IoT) fields.

Abstract

Efficient semi-transparent solar cells can extend the adoption of photovoltaics beyond standard utility-scale, commercial, or residential applications. Halide perovskites are particularly suitable in this respect owing to their tunable bandgap. The main drawbacks in the development of transparent perovskite solar cells are the high open-circuit voltage (V_oc) deficit and the difficulties in depositing high-quality thin films over large area substrates, given the low solubility of bromide and chloride precursors. In this work, passivation strategies are developed for the high bandgap Br perovskite able to reduce charge recombination and consequently improve the V_oc. The study demonstrates 1 cm² perovskite solar cells with V_oc up to 1.73 V (1.83 eV Quasi Fermi Level Splitting) and a PCE of 8.1%. The average visible transmittance (AVT) exceeds 70% by means of a bifacial light management and a record light utilization efficiency (LUE) of 5.72 is achieved. Moreover, the potential use of the technology is evaluated toward Internet of Things (IoT) application owing to a bifaciality factor of 87% along with 17% PCE under indoor lighting. Finally, the up-scaling is demonstrated by fabricating 20 cm² active area modules with PCE of 7.3% and V_oc per cell up to 1.65 V.

Publication date: September 2024

Source: Journal of Energy Chemistry, Volume 96

Author(s): Liang Wang, Chen Chen, Zirui Gan, Chenhao Liu, Chuanhang Guo, Weiyi Xia, Wei Sun, Jingchao Cheng, Yuandong Sun, Jing Zhou, Zexin Chen, Dan Liu, Wei Li, Tao Wang

There are few published reports on perovskite solar cells (PSCs) in which the BODIPY core plays a significant role in the functioning of these devices. In this work, a significant contribution of BODIPY as a dopant-free hole-transporting layer (HTL) with an outstanding power conversion efficiency (PCE) of 20.37% is presented. This demonstrates that BODIPY derivatives are a promising alternative to obtain simple and efficient organic HTLs.

Perovskite solar cells (PSCs) have become a research hotspot since their dramatic increase in power conversion efficiency (PCE), surpassing 26% due to advances in cell engineering and interfacial layers. Within the last factor, hole transporting materials play a crucial role in enhancing device performance and stability. Among several molecular building blocks, BODIPYs are attractive for the design of novel hole transporting material (HTMs) due to their outstanding photophysical and charge transport properties easily tuned by synthetic modifications. Herein, the synthesis of five new BODIPY-based HTMs PyBDP 1–5 are reported, functionalized at the meso- and α- positions with pyrenyl and arylamino units, respectively. The resulting compounds exhibit broad absorption in the visible region, remarkable thermal stability, narrow bandgaps, suitable energy levels, and good hole extraction capability, as subtracted from experimental and computational characterizations. The performance of the BODIPY derivatives as HTMs is evaluated in planar inverted (p-i-n) PSCs and compared to commonly used PTAA, resulting in highly efficient systems, reaching PCEs very close to that obtained with the reference polymer (21.51%). The incorporation of these BODIPY-based HTMs result in an outstanding PCE of 20.37% for devices including PyBDP-1 and 19.97% for devises containing PyBDP-3, thus demonstrating that BODIPY derivatives are a promising alternative to obtain simple and efficient organic HTMs.

A nanosynapse structure of SnO₂ films is demonstrated for perovskite solar cells by incorporating sodium alginate into the SnO₂ colloidal solution. Such superior SnO₂ nanostructure can enable the high quality of perovskite films that realized high power conversion efficiencies over 24% of CsMAFAPb(I _x Br_1−x )₃ solar cells.

Tin oxide (SnO₂) has been demonstrated as a promising electron transport material for perovskite solar cells (PSCs) due to its low-temperature process and high charge extraction ability. However, the key to improving the internal performance of PSCs toward unity lies in the ability of enhancing bulk SnO₂ quality and reducing the energy level mismatch between SnO₂ and perovskite layer. Herein, a facile and effective strategy to simultaneously functionalize SnO₂ structure by sodium alginate (SA) polysaccharide compound is reported. The investigations reveal that SA leads to the formation of nanosynapse structure of SnO₂ films, which allows the aligned energy levels and suppressed charge recombination, significantly enhancing carrier extraction and transport. Consequently, CsMAFAPb(I _x Br_1−x )₃ and CsPbI₂Br solar cells achieve a remarkable power conversion efficiency of 24.11% and 16.90%, respectively, based on SnO₂-SA electron transport layers (ETLs). This work offers a facile and effective way to fabricate high-performance SnO₂ ETL in PSCs.

A favorable buried interface is developed by the designed bidentate ligand (4,6-bis (diphenylphosphino) phenoxazine, 2DPP) to construct a homogeneous buried interface, reduce defect-induced recombination, and enhance interfacial carrier transport. The perovskite solar cells obtain a power conversion efficiency (PCE) of 21.9%. In addition, the device with 2DPP modification also exhibits excellent stability.

Abstract

Nickel oxide (NiO_x) is a promising hole transport layer (HTL) to fabricate efficient and large-scale inverted perovskite solar cells (PSCs) due to its low cost and superior chemical stability. However, inverted PSCs based on NiO_x are still lagging behind that of other HTL because of the poor quality of buried interface contact. Herein, a bidentate ligand, 4,6-bis (diphenylphosphino) phenoxazine (2DPP), is used to regulate the NiO_x surface and perovskite buried interface. The diphosphine Lewis base in the 2DPP molecule can coordinate both with NiO_x and lead ions at NiO_x/perovskite interface, leading to high-quality perovskite films with minimized defects. It is found that the inverted PSCs with 2DPP-modified buried interface exhibit double advantages of being both fast charge extraction and reduced nonradiative recombination, which is a combination of multiple factors including favorable energetic alignment, improved interface contact and strong binding between NiO_x/2DPP and perovskite. The optimal PSC based on 2DPP modification yields a champion power conversion efficiency (PCE) of 21.9%. The unencapsulated PSC maintains above 75% of its initial PCE in the air with a relative humidity (RH) of 30–40% for 1000 h.

Designed a difluoro-methoxylated terminal group and synthesized the corresponding asymmetric acceptor BTP-BO-4FO, which yield better V _OC-J _SC balance and achieve an impressive efficiency of 18.62% with an excellent VOC of 0.933 V. The introduction of this novel end group represents a significant advancement in achieving high efficiencies in asymmetric SMA-based OPVs.

Abstract

Developing a new end group for synthesizing asymmetric small molecule acceptors (SMAs) is crucial for achieving high-performance organic photovoltaics (OPVs). Herein, an asymmetric small molecule acceptor, BTP-BO-4FO, featuring a new difluoro-methoxylated end-group is reported. Compared to its symmetric counterpart L8-BO, BTP-BO-4FO exhibits an upshifted energy level, larger dipole moment, and more sequential crystallinity. By adopting two representative and widely available solvent additives (1-chloronaphthalene (CN) and 1,8-diiodooctane (DIO)), the device based on PM6:BTP-BO-4FO (CN) photovoltaic blend demonstrates a power conversion efficiency (PCE) of 18.62% with an excellent open-circuit voltage (V _OC) of 0.933 V, which surpasses the optimal result of L8-BO. The PCE of 18.62% realizes the best efficiencies for binary OPVs based on SMAs with asymmetric end groups. A series of investigations reveal that optimized PM6:BTP-BO-4FO film demonstrates similar molecular packing motif and fibrillar phase distribution as PM6:L8-BO (DIO) does, resulting in comparable recombination dynamics, thus, similar fill factor. Besides, it is found PM6:BTP-BO-4FO possesses more efficient charge generation, which yields better V _OC–J _SC balance. This study provides a new ending group that enables a cutting-edge efficiency in asymmetric SMA-based OPVs, enriching the material library and shed light on further design ideas.

Publication date: September 2024

Source: Journal of Energy Chemistry, Volume 96

Author(s): Jinwen Gu, Xianggang Sun, Pok Fung Chan, Xinhui Lu, Peng Zeng, Jue Gong, Faming Li, Mingzhen Liu

Publication date: 17 July 2024

Source: Joule, Volume 8, Issue 7

Author(s): Min Jae Paik, Yu Young Kim, Jongbeom Kim, Jaewang Park, Sang Il Seok

Publication date: 19 June 2024

Source: Joule, Volume 8, Issue 6

Author(s): Deniz Turkay, Kerem Artuk, Xin-Yu Chin, Daniel A. Jacobs, Soo-Jin Moon, Arnaud Walter, Mounir Mensi, Gaëlle Andreatta, Nicolas Blondiaux, Huagui Lai, Fan Fu, Mathieu Boccard, Quentin Jeangros, Christian M. Wolff, Christophe Ballif

Bis[2-(diphenyl phosphate) phenyl] ether oxide (DPEPO) is incorporated as the interfacial passivation material of the perovskite/electron transport layer (ETL). Through the coordination interactions between the P=O group in DPEPO and the undercoordinated Pb²⁺, the defects in perovskite crystals are effectively eliminated, the interface non-radiative recombination is reduced, and the electron transport from perovskite to the ETL is promoted. Incorporation of DPEPO passivation layer leads to increased PCE of perovskite solar cell (PSC) from 22.26% to 24.17%.

Inverted (p-i-n) perovskite solar cells (PSCs) are advantageous in terms of easy fabrication, low-temperature processibility, negligible hysteresis, and excellent compatibility with the tandem devices in comparison with the regular (n-i-p) counterparts. Hole-blocking layer is crucial for efficient electron transport of inverted PSCs, and only a single hole-blocking layer of bathocuproine (BCP) is used typically. Herein, bis[2-(diphenylphosphino)phenyl] ether oxide (DPEPO) with a deep highest occupied molecular orbital (HOMO) energy level is incorporated atop of perovskite film as an auxiliary hole-blocking layer, resulting in an enhanced electron transport of inverted PSC devices. The P=O group within DPEPO can coordinate with Pb²⁺ cations of perovskite, leading to passivation of surface defects of perovskite. Besides, incorporation of DPEPO hole-blocking layer prohibits undesired hole transport from perovskite to PCBM electron transport layer (ETL), thus suppressing non-radiative electron–hole recombination. As a result, combined with BCP hole-blocking layer, inverted PSC devices based on double hole-blocking layers exhibit a decent power conversion efficiency (PCE) of 24.17% with a high open-circuit voltage (V _oc) of 1.15 V which dramatically surpasses that based on single hole-blocking layer (22.26%). Moreover, incorporation of hydrophobic DPEPO helps to improve the ambient and thermal stabilities of inverted PSC devices.

The electrical properties and surface morphology of SnSe₂-SnO₂ are improved. The CA effectively passivates the defects on the surface and grain boundary of perovskite due to it containing more abundant active sites. The synergism of SnSe₂QDs and CA releases the residual stress and regulates the energy level arrangement at the top and bottom interface of perovskite.

Abstract

Non-radiative recombination losses limit the property of perovskite solar cells (PSCs). Here, a synergistic strategy of SnSe₂QDs doping into SnO₂ and chlorhexidine acetate (CA) coating on the surface of perovskite is proposed. The introduction of 2D SnSe₂QDs reduces the oxygen vacancy defects and increases the carrier mobility of SnO₂. The optimized SnO₂ as a buried interface obviously improves the crystallization quality of perovskite. The CA containing abundant active sites of ─NH₂/─NH─, ─C═N, CO, ─Cl groups passivate the defects on the surface and grain boundary of perovskite. The alkyl chain of CA also improves the hydrophobicity of perovskite. Moreover, the synergism of SnSe₂QDs and CA releases the residual stress and regulates the energy level arrangement at the top and bottom interface of perovskite. Benefiting from these advantages, the bulk and interface non-radiative recombination loss is greatly suppressed and thereby increases the carrier transport and extraction in devices. As a result, the best power conversion efficiency (PCE) of 23.41% for rigid PSCs and the best PCE of 21.84% for flexible PSCs are reached. The rigid PSC maintains 89% of initial efficiency after storing nitrogen for 3100 h. The flexible PSCs retain 87% of the initial PCE after 5000 bending cycles at a bending radius of 5 mm.

V_Se is a kind of detrimental deep-level defect in Sb₂Se₃ thin films which induces serious carrier trapping. The effective passivation of defects is achieved by introducing trace amount of sulfur into Sb₂Se₃ film by transforming V_Se to S_Se. S_Se defects are benign and do not trap charge carriers, thus improving the carrier lifetime and device performance.

Abstract

Binary antimony selenide (Sb₂Se₃) is a promising inorganic light-harvesting material with high stability, nontoxicity, and wide light harvesting capability. In this photovoltaic material, it has been recognized that deep energy level defects with large carrier capture cross section, such as V_Se (selenium vacancy), lead to serious open-circuit voltage (V _OC) deficit and in turn limit the achievable power conversion efficiency (PCE) of Sb₂Se₃ solar cells. Understanding the nature of deep-level defects and establishing effective method to eliminate the defects are vital to improving V _OC. In this study, a novel directed defect passivation strategy is proposed to suppress the formation of V_Se and maintain the composition and morphology of Sb₂Se₃ film. In particular, through systematic study on the evolution of defect properties, the pathway of defect passivation reaction is revealed. Owing to the inhibition of defect-assisted recombination, the V _OC increases, resulting in an improvement of PCE from 7.69% to 8.90%, which is the highest efficiency of Sb₂Se₃ solar cells prepared by thermal evaporation method with superstrate device configuration. This study proposes a new understanding of the nature of deep-level defects and enlightens the fabrication of high quality Sb₂Se₃ thin film for solar cell applications.

Trivalent antimony is used to counter-dope the oxidized Sn-based perovskite by replacing divalent tin in the crystal lattice. It effectively decreases the doping levels in tin halide perovskites down to 10¹⁴ cm⁻³, and meanwhile passivates deep-level defects induced by iodine vacancies. The resultant devices show a relative enhancement of 31.4% in the average efficiency as well as improved shelf-storage stability.

Abstract

Tin (Sn) -based perovskite solar cells (PSCs) normally show low open circuit voltage due to serious carrier recombination in the devices, which can be attributed to the oxidation and the resultant high p-type doping of the perovskite active layers. Considering the grand challenge to completely prohibit the oxidation of Sn-based perovskites, a feasible way to improve the device performance is to counter-dope the oxidized Sn-based perovskites by replacing Sn²⁺ with trivalent cations in the crystal lattice, which however is rarely reported. Here, the introduction of Sb³⁺, which can effectively counter-dope the oxidized perovskite layer and improve the carrier lifetime, is presented. Meanwhile, Sb³⁺ can passivate deep-level defects and improve carrier mobility of the perovskite layer, which are all favorable for the photovoltaic performance of the devices. Consequently, the target devices yield a relative enhancement of the power conversion efficiency (PCE) of 31.4% as well as excellent shelf-storage stability. This work provides a novel strategy to improve the performance of Sn-based PSCs, which can be developed as a universal way to compensate for the oxidation of Sn-based perovskites in optoelectronic devices.

This work proposes the concept of an all-round detoxification strategy of  “lead isolation and capture” on perovskite solar cells (PSCs) for the first time, and the adequate in vivo experiments in mice reveal that this material has significant inhibitory effect on the toxicity of perovskite. This strategy can further enhance the device performance, achieving an impressive power conversion efficiency of 25.19%.

Abstract

Perovskite solar cells (PSCs) are developed rapidly in efficiency and stability in recent years, which can compete with silicon solar cells. However, an important obstacle to the commercialization of PSCs is the toxicity of lead ions (Pb²⁺) from water-soluble perovskites. The entry of free Pb²⁺ into organisms can cause severe harm to humans, such as blood lead poisoning, organ failure, etc. Therefore, this work reports a “lead isolation-capture” dual detoxification strategy with calcium disodium edetate (EDTA Na-Ca), which can inhibit lead leakage from PSCs under extreme conditions. More importantly, leaked lead exists in a nontoxic aggregation state chelated by EDTA. For the first time, in vivo experiments are conducted in mice to systematically prove that this material has a significant inhibitory effect on the toxicity of perovskites. In addition, this strategy can further enhance device performance, enabling the optimized devices to achieve an impressive power conversion efficiency (PCE) of 25.19%. This innovative strategy is a major breakthrough in the research on the prevention of lead toxicity in PSCs.

We multidimensionally reveal the relationship between passivation strength of organic passivator on perovskite film and the spin-state electronic structure of intermediate donor skeleton. Agreeing well with the calculated amounts of transferred electron between D−A pairs, the best benzene-amide pair delivers a champion efficiency of 15.51 % for carbon-based, all-inorganic CsPbI₂Br solar cell and 24.20 % in an inverted (Cs_0.05MA_0.05FA_0.9)Pb(I_0.93Br_0.07)₃ cell.

Abstract

The passivation of the defects derived from rapid-crystallization with electron-donating molecules is always a prerequisite to obtain desirable perovskite films for efficient and stable solar cells, thus, the in-depth understanding on the correlations between molecular structure and passivation capacity is of great importance for screening passivators. Here, we introduce the double-ended amide molecule into perovskite precursor solution to modulate crystallization process and passivate defects. By regulating the intermediate bridging skeletons with alkyl, alkenyl and benzene groups, the results show the passivation strength highly depends on the spin-state electronic structure that serves as an intrinsic descriptor to determine the intramolecular charge distribution by controlling orbital electron transfer from the donor segment to acceptor segment. Upon careful optimization, the benzene-bridged amide molecule demonstrates superior efficacy on improving perovskite film quality. As a physical proof-of-concept, the carbon-based, all-inorganic CsPbI₂Br solar cell delivers a significantly increased efficiency of 15.51 % with a remarkably improved stability. Based on the same principle, a champion efficiency of 24.20 % is further obtained on the inverted (Cs_0.05MA_0.05FA_0.9)Pb(I_0.93Br_0.07)₃ solar cell. These findings provide new fundamental insights into the influence of spin-state modulation on effective perovskite solar cells.

Nature Communications, Published online: 16 May 2024; doi:10.1038/s41467-024-48552-2

Nature Materials, Published online: 16 May 2024; doi:10.1038/s41563-024-01895-z

A low-toxic Lewis base ligand solvent, N-ethyl-2-pyrrolidone (NEP), is introduced into perovskite fabrication during vacuum-flash. The optimized nucleation process provides a high efficiency of 24.19% for perovskite solar cells and a certified efficiency of 23.28% for modules. The equally high efficiency of cells and modules demonstrates commercialization potential of perovskite solar cells with NEP.

Abstract

Efficiency reduction in perovskite solar cells (PSCs) during the magnification procedure significantly hampers commercialization. Vacuum-flash (VF) has emerged as a promising method to fabricate PSCs with consistent efficiency across scales. However, the slower solvent removal rate of VF compared to the anti-solvent method leads to perovskite films with buried defects. Thus, this work employs low-toxic Lewis base ligand solvent N-ethyl-2-pyrrolidone (NEP) to improve the nucleation process of perovskite films. NEP, with a mechanism similar to that of N-methyl-2-pyrrolidone in FA-based perovskite formation, enhances the solvent removal speed owing to its lower coordination ability. Based on this strategy, p–i–n PSCs with an optimized interface attain a power conversion efficiency (PCE) of 24.19% on an area of 0.08 cm². The same nucleation process enables perovskite solar modules (PSMs) to achieve a certified PCE of 23.28% on an aperture area of 22.96 cm², with a high geometric fill factor of 97%, ensuring nearly identical active area PCE (24%) in PSMs as in PSCs. This strategy highlights the potential of NEP as a ligand solvent choice for the commercialization of PSCs.

The trap state at the surfaces and grain boundaries of perovskite is one of the major obstacles to the further commercialization of flexible perovskite solar cells (FPSCs). The study reveals the interaction of fluorinated propylamine hydrochloride with precursor and defect states of perovskite films toward efficient flexible solar cells. This work provides valuable insights for the future design of passivation molecules with efficient FPSCs and high mechanical robustness.

Abstract

The trap state at the surfaces and grain boundaries of perovskite is one of the major obstacles to the further commercialization of flexible perovskite solar cells (FPSCs). Herein, two innovative multifunctional fluorinated propylamine salt 2,2,3,3,3-pentafluoropropylamine hydrochloride (PFPACl) and 3,3,3-triflupropylamine hydrochloride (TFPACl) are in situ introduced onto the photo absorbing layer to improve the performance of the FPSCs. The nuclear magnetic resonance (NMR) spectroscopy indicates strong interactions of both PFPACl and TFPACl with the perovskite precursor components. For the first time, the structures of the supramolecular complexes formed by two additives with FAI are deduced from NOESY NMR data, thus pointing to the importance of the preorganization of the perovskite components in solution before film casting. The experiments and density functional theory（DFT) calculations reveal that PFPACl is likely dissociated more into the form of R-NH₃ ⁺-Cl⁻ due to the higher electronegativity of the fluoroalkyl tail. Therefore, PFPA⁺ binds more strongly to V_FA defects than TFPA⁺, and anion Cl⁻ has strong enough interaction with V_FAI and uncoordinated Pb²⁺, leading to homogeneous coverage of PFPACl on the entire surface of the perovskite films and better energy alignment with the hole transport layer. Consequently, PFPACl-treated FPSCs achieved a relatively high PCE of 23.59% with excellent mechanical robustness and operational stability.

A simple and low-cost wide-band gap coumarin-anthracene-based D-A dyad was designed and synthesized. The molecule when applied as an acceptor into PTB7-Th : DICTF blend exhibited an impressive power conversion efficiency of 14.91 % in ternary organic solar cells.

Abstract

Asymmetric wide-band gap fullerene-free acceptors (FFAs) play a crucial role in organic solar cells (OSCs). Here, we designed and synthesized a simple asymmetric coumarin-anthracene conjugate named CA-CN with optical band gap of 2.1 eV in a single-step condensation reaction. Single crystal X-ray structure analysis confirms various multiple intermolecular non-covalent interactions. The molecular orbital energy levels of CA-CN estimated from cyclic voltammetry were found to be suitable for its use as an acceptor for OSCs. Binary OSCs fabricated using CA-CN as acceptor and PTB7-Th as the donor achieve a power conversion efficiency (PCE) of 11.13 %. We further demonstrate that the insertion of 20 wt % of CA-CN as a third component in ternary OSCs with PTB7-Th : DICTF as the host material achieved an impressive PCE of 14.91 %, an improvement of ~43 % compared to the PTB7-Th : DICTF binary device (10.38 %). Importantly, the ternary blend enhances the absorption coverage from 400 to 800 nm and improves the morphology of the active layer. The findings highlight the efficacy of an asymmetric design approach for FFAs, which paves the way for developing high-efficiency OSCs at low cost.

This study demonstrates the impressive outdoor stability of perovskite solar cells previously tested indoors. The cells are monitored for six months under two realistic operating conditions. The cell connected to a resistance remains stable, whereas the one with maximum power point tracking and current–voltage curve tracing starts degrading. Results suggest that concealed electronic equipment malfunctions trigger this premature degradation.

Perovskite solar cells (PSCs) have sparked great excitement in the photovoltaics community due to their remarkable efficiency, flexibility, and ability to be synthesized at low cost. However, their instability poses a major roadblock to their widespread adoption. Recognizing this challenge, this work describes the performance of stable PSCs operating under real-life conditions in the Paris area. Two state-of-the-art 2D/3D (HOOC(CH₂)₄NH₃)2PbI₄/CH₃NH₃PbI₃ encapsulated cells are considered—one with maximum power point tracking and hourly current–voltage curve measurements, and another connected to a fixed resistive load. Their performance is compared over six months, and a detailed analysis is conducted on the cells’ hysteresis and electrical response to varying weather conditions. Although the first cell starts to degrade after a few months of operation, the second one remains remarkably stable, highlighting critical issues with outdoor tracking. Given that the stability of this PSC architecture has already been established under controlled standard conditions for over one year, these exciting findings pave the way for the commercialization of perovskite-based photovoltaic devices.

Herein, a perovskite layer with inverse opal (PVSK–IO) structure is used to fabricate perovskite solar cells. It is found that the PVSK–IO not only exhibits a remarkable slow-photon effect for enhancing light absorption, but also promotes the carrier transfer by expanding the contact area with hole-transport layer.

Over the past decade, perovskite solar cells (PSCs) have witnessed a remarkable surge in power conversion efficiency (PCE). However, the electrical output performance of PSCs is dependent on the incident angle of solar radiation, and energy loss occurs during photovoltaic conversion when light impinges at angles. Herein, a perovskite-light-absorbed layer with inverse opal structure is used to fabricate PSCs and reduce the angular dependence of the performance. In the results, it is demonstrated that ordered periodic perovskite inverse opal (PVSK–IO) not only exhibits a remarkable slow-photon effect for enhancing the absorption of sunlight near the photonic bandgap (PBG), but also promotes the carrier transfer by expanding the contact area with hole-transport layer. Moreover, the slow-photon region of PBG can be intentionally tuned by changing the direction of sunlight illumination, thereby more intuitively delaying and storing light in the PVSK–IO layer. As a consequence, the slow-photon effect originated from the PVSK–IO structure efficiently improves the short-circuit current density, resulting in a higher PCE than that of planar devices under the irradiation from different incident angles. In this research, a rational strategy is offered for enhancing the performance of PSCs while alleviating their angular dependence.

Through cyanation on quinoxaline-based small-molecule acceptors (SMAs), BQx-CN with a mono-cyanide group exhibits down-shifted energy levels and stronger intermolecular stacking for rapid charge transfer and transport. When employed in organic solar cells (OSCs), the BQx-CN-based devices yield a higher efficiency of 18.8%, which is one of the highest values for asymmetric SMA-based OSCs.

Abstract

Cyanation is a common chemical modification strategy to fine-tune the energy levels and molecular packing of organic semiconductors, especially materials used in organic solar cells (OSCs). Generally, cyanation is used to modify the end groups of high-performance small-molecule acceptors (SMAs). However, the cyanation strategy has not been investigated on the central backbone of SMAs, which could introduce stronger intermolecular interaction and enhance the π–π stacking for rapid charge transport. This paper, for the first time, reports a new cyanation strategy on the central benzo-quinoxaline core and synthesizes two novel A-DA'D-A type SMAs, named BQx-CN and BQx-2CN, with mono- and di-cyanide groups, respectively. Through tailoring the number of CN groups, the BQx-CN-based OSC exhibits the best device performance of 18.8%, which is significantly higher than the non-cyano BQx-based one. The reason for the superior performance of BQx-CN-based devices can be attributed to the fine-tuned energy level, stronger packing, and ideal phase segregation, which lead to superior exciton dissociation, faster charge transport, and suppressed recombination, therefore the highest fill factor (FF) and power conversion efficiencies (PCE). The research demonstrates the effectiveness of the cyanation strategy on the central core of SMAs for enhanced molecular packing and better performance of OSCs.