Chen Weijie

Herein, both two-terminal (2-T) and four-terminal (4-T) perovskite/perovskite tandem solar cells are simulated and optimized. After device optimization, an optimal power conversion efficiency (PCE) of 27.86% is obtained based on 2-T CsPbI₂Br/MASn_0.5Pb_0.5I₃ tandem device, and a 4-T all-perovskite tandem solar cell with a high PCE of 30.45% is obtained.

Compared with the single-junction perovskite solar cells, the perovskite/perovskite tandem solar cells have the advantages of lower cost and higher power conversion efficiency (PCE). Herein, both two-terminal (2-T) and four-terminal (4-T) perovskite/perovskite tandem solar cells with all-inorganic perovskite as the top cell absorption layer and narrow bandgap perovskite MASn_0.5Pb_0.5I₃ material as the bottom cell absorption layer are studied. To effectively improve the photon absorption ratio and performance of the 4-T tandem device, both reflection and parasitic absorption should be reduced. Afterward, by optimizing the doping concentration of the carrier transport layer, a 4-T all-perovskite tandem solar cell with a high PCE of 30.45% is obtained. For the 2-T all-perovskite tandem device, the all-inorganic perovskites with different halogen components (CsPbI_3−x Br _x , 0 ≤ x ≤ 3) are used as the absorption layer of the top cell, respectively. Through the optimization of the current matching of the subcell, the photoelectric field distribution, the parasitic absorption of the device, etc., an optimal PCE of 27.86% is obtained based on 2-T CsPbI₂Br/MASn_0.5Pb_0.5I₃ tandem device. This study provides a guide for achieving high performance perovskite/perovskite tandem solar cells.

Two fused-ring electron acceptors with linear n-heptane chains or bulky cyclohexylmethyl chains on the pyrrole motif are synthesized to reveal the impact of inner linear alkyl chain cyclization on physicochemical property, molecular packing behaviors, charge transports, film morphology, and photovoltaic performance.

By changing the structures of the side chain on the backbone of the Y6 acceptor, many Y-series acceptors have been synthesized to investigate the relationships between structures and properties of the fused-ring electron acceptors (FREAs). However, not much attention has been paid to the effects of cycloalkane substituents on optoelectronic, morphological, and photovoltaic properties of the FREAs. Here, a brand-new FREA D12 is developed by incorporating cyclohexylmethyl functional groups into the pyrrole rings of the backbone of the Y6 acceptor, and a similar compound E12 with the linear n-heptane side chains is also synthesized for comparison. After the cyclization of the alkyl side-chain, the molecular orientation of D12 exhibits favorable face-on dominant, which endows D12 with higher charge mobility. Consequently, the organic solar cells (OSCs) with PM6 as donor and D12 as acceptor deliver the maximum power conversion efficiency of 17.3%, along with an excellent fill factor of 0.794, which is much higher than those of the PM6:E12-based OSCs. The results reveal that introducing an inner cyclized alkyl chain on the pyrrole motif is a simple and feasible strategy to regulate molecular orientation and improve photovoltaic properties, which might provide guidelines for developing high-performance electron acceptors.

A dual-functional piperidyl ionic liquid for enhancing the performance of perovskite solar cells is demonstrated by passivating intrinsic defects in the perovskite absorber and simultaneously doping the hole transport layer with improved hydrophobicity. The optimal device produces a champion efficiency of 23.34% with a significantly increased stability in moisture air.

Perovskite solar cells (PSCs) have recently attracted rapid interest for harvesting solar energy. However, the defects in perovskite absorber and vulnerability of charge-transporting layer lead to unsatisfying stability, which limits their practical applications. Herein, we demonstrate that the addition of a piperidyl ionic liquid, that is, 1-butyl-1-methylpiperidinium bis(trifluoromethyl sulfonyl)imide ([BMP]⁺[TFSI]⁻), can serve as a dual functional additive for passivating the intrinsic defects in perovskite and simultaneously improving the hydrophobicity of hole transport layer. Consequently, the power conversion efficiency for the optimal planar PSCs significantly increases from 21.07% to 23.34%. Impressively, the unencapsulated champion cells display promising stability with a reservation over 80% of the initial efficiency after exposure to moisture air (65% ± 5% relative humidity) for 1600 h. This work provides a facile strategy toward enhancing the efficiency and stability of PSCs.

Two solution-processable functional polymers, namely P-PDI and 2DP-PDI, are synthesized by dimensional tuning strategy. The quasi-2D polymer (2DP-PDI) exhibited matched energy levels and excellent charge transport properties. High efficiency of 24.20% has been demonstrated when 2DP-PDI is used as a functional interfacial layer in perovskite solar cells, coupled with dramatically improved stability.

Abstract

The hygroscopic dopants used in Spiro-OMeTAD hole transport material (HTM) in state-of-the-art perovskite solar cells (PSCs) inevitably induce premature degradation of the devices. Here, two multifunctional polymer interface materials based on the perylene diimides (PDI) unit are developed. It is found that quasi-two-dimensional (2D) polymer 2DP-PDI can form a denser film and exhibit better hydrophobicity than linear polymer P-PDI. Importantly, 2DP-PDI can passivate the surface defects and extract hole carriers of perovskite film more effectively, leading to much reduced nonradiative recombination loss. With polymer interface material between the perovskite and HTM layers, the optimized device using 2DP-PDI and P-PDI yields a champion PCE of 24.20% and 23.09%, respectively, along with significantly improved stability, whereas the control device shows a lower efficiency of 22.23%. These results suggest that developing multifunctional polymer interface materials can be a promising strategy to improve the efficiency and stability of PSCs.

A synergy strategy of ionic-liquid methylammonium acetate (MAAc) and molecular phenylurea additives is developed to doctor-blade MAPbI₃ perovskite solar cells (PSCs) with a device structure of ITO/SnO₂/MAPbI₃/Spiro-OMeTAD/Ag. Impressive power conversion efficiency (PCE) of 20.34% is achieved under the humidity over 80%, which is the highest efficiency for one-step solution-processed MAPbI₃ PSCs without antisolvent assistance.

Abstract

Perovskite solar cells (PSCs) have emerged as one of the most promising and competitive photovoltaic technologies, and doctor-blading is a facile and robust deposition technique to efficiently fabricate PSCs in large scale, especially matching with roll-to-roll process. Herein, it demonstrates the encouraging results of one-step, antisolvent-free doctor-bladed methylammonium lead iodide (CH₃NH₃PbI_3, MAPbI₃) PSCs under a wide range of humidity from 45% to 82%. A synergy strategy of ionic-liquid methylammonium acetate (MAAc) and molecular phenylurea additives is developed to modulate the morphology and crystallization process of MAPbI₃ perovskite film, leading to high-quality MAPbI₃ perovskite film with large-size crystal, low defect density, and ultrasmooth surface. Impressive power conversion efficiency (PCE) of 20.34% is achieved for doctor-bladed PSCs under the humidity over 80% with a device structure of ITO/SnO₂/MAPbI₃/Spiro-OMeTAD/Ag. It is the highest PCEs for one-step solution-processed MAPbI₃ PSCs without antisolvent assistance. The research provides a facile and robust large-scale deposition technique to fabricate highly efficient and stable PSCs under a wide range of humidity, even with the humidity over 80%.

The inclined fluorine (F) sputtering process can simultaneously implement an antireflection effect of F coating and the F doping effect on TiO₂ electron transport layer. Consequently, the short-circuit current density of F coating and doping perovskite solar cell is improved from 25.05 to 26.01 mA cm⁻², and the power conversion efficiency increases from 24.17% to 25.30%.

Abstract

Increase in incident light and surface modification of the charge transport layer are powerful routes to achieve high-performance efficiency of perovskite solar cells (PSCs) by improving the short-circuit current density (J _SC) and charge transport characteristics, respectively. However, few techniques are studied to reduce reflection loss and simultaneously improve the electrical performance of the electron transport layer (ETL). Herein, an inclined fluorine (F) sputtering process to fabricate high-performance PSCs is proposed. The proposed process simultaneously implements the antireflection effect of F coating and the effect of F doping on a TiO₂ ETL, which increases the amount of light transmitted into the PSC due to the extremely low refractive index (≈1.39) and drastically improves the electrical properties of TiO₂. Consequently, the J _SC of the F coating and doping perovskite solar cell (F-PSC) increased from 25.05 to 26.01 mA cm⁻², and the power conversion efficiency increased from 24.17% to 25.30%. The unencapsulated F-PSC exhibits enhanced air stability after 900 h of exposure to ambient environment atmosphere (30% relative humidity, 25 °C under dark condition). The inclined F sputtering process in this study can become a universal method for PSCs from the development stage to commercialization in the future.

In this study, structure–property relationships in the non-fullerene PM6:Y6 blend are established. The interfacial microstructure of two charge transfer states is identified, and it is found that recombination across the amorphous-PM6:crystalline-Y6 interface controls open-circuit voltage. It is concluded that crystalline Y6 increases non-radiative recombination but is necessary for charge transport; thus, device optimization requires morphological tradeoffs.

Abstract

Performance of nonfullerene-based organic solar cells is largely dependent on the donor:acceptor blend morphology, which is initially tuned by composition. However, morphological design rules are difficult to identify due to the complex relationship between composition-dependent phase behavior and performance properties. In this study, the authors are able to establish a direct link between PM6:Y6 film morphology and device properties by combining grazing-incidence wide-angle X-ray scattering with highly sensitive Fourier transform photocurrent spectroscopy. By analyzing properties across the full composition range, interfacial microstructure and the corresponding charge transfer (CT) states are identified and direct structure–property relationships are established. The results indicate that open-circuit voltage is controlled by the CT state at amorphous-PM6:crystalline-Y6 interfaces. Crystalline Y6 is found to increase both transport and non-radiative recombination, suggesting that morphological tradeoffs may be necessary for overall device optimization.

The technique of printing a low-melting-point alloy as top electrodes in organic photovoltaics via blade coating is introduced. All printed organic solar cells, in which the alloy electrode is blade coated and the other organic functional layers are prepared by flexible micro-comb printing, exhibiting a power conversion efficiency up to 16.07%.

Abstract

All printing of organic photovoltaics (OPVs) including the top electrode is highly desirable for achieving cost-effective, high-throughput, and large-area photovoltaic manufacturing. Here, the printing of a low-melting-point alloy as top electrodes in OPVs via blade coating is investigated. The Field's metal (FM) with the melting point of 62 °C is adopted for the top electrodes, because FM can be printed under moderate temperatures without harming the active layers while remaining solid state under solar irradiation. The correlations between the processing parameters and properties of the blade-coated electrodes are elucidated. OPVs based on the D18:Y6 active layer and blade-coated FM electrodes achieve a highest power conversion efficiency of 17.28%. The OPVs with FM-electrode demonstrate much higher thermal stability than that of the Ag-electrode devices. All-printed OPVs, in which the FM electrode is blade coated and the other layers are prepared by flexible micro-comb printing, exhibit an efficiency of 16.07%. The results represent the records of evaporation-free and all-printed OPVs, demonstrating that printing FM as OPV electrodes is a cost-effective and time-saving strategy to substitute the vacuum-evaporated metals, as well as a feasible route toward high-performance all-printed OPVs.

Potassium 1,1,2,2,3,3-hexafluoroprop-ane-1,3-disulfonimide (KHFDF) is introduced into PbI₂ precursor solution to passivate various defects and improve the crystalline quality of perovskite films. Assisted by Lewis coordination, hydrogen bonding, and ionic interaction between KHFDF and perovskite, better crystal orientation and reduced trap-state density perovskite crystallites are achieved, yielding a power conversion efficiency of 24.15% and long-term humidity stability and thermostability.

Abstract

Organic-inorganic lead halide perovskite are promising photovoltaic materials, but their intrinsic defects and crystalline quality severely deteriorate the solar cells efficiency and stability. Herein, potassium 1,1,2,2,3,3-hexafluoroprop-ane-1,3-disulfonimide (KHFDF) is introduced into PbI₂ precursor solution to passivate various defects and improve the crystalline quality of perovskite films. It is found that KHFDF can inhibit PbI₂ crystallization, thus tuning the crystal orientation and growth of perovskite films. Furthermore, KHFDF with dual-functional sulfonyl group cannot only passivate grain boundaries (GBs), but also passivate the defects at GBs via strong interaction with undercoordinated Pb²⁺ and/or hydrogen bonding with FA⁺, while the K⁺ counter cations allow ionic interaction with undercoordinated I⁻. As a result, the KHFDF-modified films exhibit high quality with a larger grain size and a reduced trap-state density, thereby suppressing the trap-state nonradiative recombination. And the devices show a champion efficiency up to 24.15%, benefiting from a sharp enhancement of open-circuit voltage (V _oc) of 1.183 V and fill factor of 81.78%. In addition, due to the enhanced humidity tolerance and chemical structure stability, the devices exhibit excellent long-term humidity and thermal stability without encapsulation.

High-quality Sn–Pb perovskites and excellent contacts at the perovskite/C₆₀ interface are developed by introducing a one-in-all modifier. The introduction of cysteine hydrochloride (CysHCl) to Sn–Pb perovskites restrains non-radiative recombination and facilitates electron transfer. Consequently, the CysHCl-processed devices achieve the highest power conversion efficiency (PCE) of 22.15% for low-bandgap (LBG) Sn–Pb perovskite solar cell (PSC) and 26.16% for all-perovskite monolithic tandem devices.

Abstract

All-perovskite tandem solar cells (TSCs) hold great promise in terms of ultrahigh efficiency, low manufacturing cost, and flexibility, stepping forward to the next-generation photovoltaics. However, their further development is hampered by the relatively low performance of low-bandgap (LBG) tin (Sn)–lead (Pb) perovskite solar cells (PSCs). Improving the carrier management, including suppressing trap-assisted non-radiative recombination and promoting carrier transfer, is of great significance to enhance the performance of Sn–Pb PSCs. Herein, a carrier management strategy is reported for using cysteine hydrochloride (CysHCl) simultaneously as a bulky passivator and a surface anchoring agent for Sn–Pb perovskite. CysHCl processing effectively reduces trap density and suppresses non-radiative recombination, enabling the growth of high-quality Sn–Pb perovskite with greatly improved carrier diffusion length of >8 µm. Furthermore, the electron transfer at the perovskite/C₆₀ interface is accelerated due to the formation of surface dipoles and favorable energy band bending. As a result, these advances enable the demonstration of champion efficiency of 22.15% for CysHCl-processed LBG Sn–Pb PSCs with remarkable enhancement in both open-circuit voltage and fill factor. When paired with a wide-bandgap (WBG) perovskite subcell, a certified 25.7%-efficient all-perovskite monolithic tandem device is further demonstrated.

A layer of D-A-D small molecule film [triphenylamine-2,1,3-benzothiadiazole-triphenylamine (TBT)] is deposited at the NiO _x /MAPbI_3–x Cl _x interface, and the interface microstructure and crystallization control are realized. The interaction of TBT with perovskite results in a better alignment of energy levels and reduced interfacial defects, a satisfactory power conversion efficiency of 21.84%, and long-term stability of over 1000 h.

Nickel oxide (NiO _x ) is one of the most widely used inorganic hole transport materials for inverted perovskite solar cells (PSCs), which has the advantages of low cost, easy preparation, and good stability. However, the energy-level mismatch and interfacial redox reactions at the NiO _x /perovskite interface limit the performance of NiO _x -based PSCs. Herein, triphenylamine-2,1,3-benzothiadiazole-triphenylamine (TBT) small-molecule material is first used as an interfacial modification layer between NiO _x and perovskite. The deposition of TBT on NiO _x helps to hinder the contact between NiO _x and perovskite, improves the electrical conductivity, passivates interfacial defects, and inhibits the recombination of interfacial carriers. TBT makes the valance band top energy level of NiO _x better match that of perovskite and promotes the hole transfer at NiO _x /perovskite interface, and the hole transfer rate increases from 2.19 × 10¹⁰ to 4.12 × 10¹⁰ s⁻¹. The TBT-based device obtains a champion power conversion efficiency (PCE) of 21.84%, much higher than the control device (18.62%). Furthermore, the optimized device which is conserved in 30 ± 5% relative humidity and 25 °C environments more than 1000 h retains 90% of the initial efficiency. A effective strategy to improve the PCE and stability of NiO _x -based PSCs is provided.

Spacer cations with different substituents (PMA, p-MeOPMA, and p-FPMA) are found to mainly affect the crystal growth and film quality of quasi-2D perovskites. Interestingly, unsubstituted benzylamine (PMA) shows improved crystallinity and crystal orientation, enabling suppressed trap densities, efficient charge transport, better optoelectronic properties, and device performance based on quasi-2D perovskites.

Quasi-two-dimensional perovskite solar cells (quasi-2D PSCs) have drawn significant attention and are rapidly developing owing to the impressive stability of the materials and devices. However, there are no reliable guidelines for designing and selecting suitable organic spacer cations to achieve high power conversion efficiency (PCE) in quasi-2D PSCs. Herein, the effects of the spacer cations with different substituents, i.e., benzylamine (PMA), 4-methoxybenzylamine (p-MeOPMA), and 4-fluorobenzylamine (p-FPMA), on the optoelectronic properties and device performance of quasi-2D perovskites are systematically investigated. It is found that the spacer cations with different substituents mainly affect the crystal growth and film quality of quasi-2D perovskites. Interestingly, quasi-2D perovskites based on p-MeOPMA or p-FPMA exhibit poor crystallinity and crystal orientation, while quasi-2D perovskite based on the unsubstituted PMA shows improved crystallinity and crystal orientation, which enables suppressed trap densities and efficient charge transport. The PMA-based quasi-2D perovskite (nominal n = 3) solar cell exhibits the highest PCE of 13.58%. These results demonstrate that the rational regulation of organic spacer cations plays a crucial role in improving the crystallinity and crystal orientation of perovskite films and elucidate key guiding rules for organic spacer cations for high-performance quasi-2D PSCs.

Molybdenum oxide (MoO_3−x ) is successfully used as an efficient hole-selective contact material; however, there are lack of effective modulations of its carrier transport capability. The oxidation states and hole selectivity of MoO_3−x by doping V⁵⁺, Nb⁵⁺, or Ta⁵⁺ are successfully tuned, achieving a record high conversion efficiency of 18.37% for solution-processed MoO_3−x /p-Si heterostructure solar cells.

Molybdenum oxide (MoO_3−x , x < 3) has been successfully used as an efficient hole-selective contact material for crystalline silicon heterojunction solar cells. The carrier transport capability strongly depends on its work function, that is, oxygen vacancies; however, there are lack of effective methods to modulate the multiple oxidation states. Herein, the oxidation states of solution-processed MoO_3−x by doping Nb⁵⁺ to improve its hole-selective contact performance with silicon are tuned. With the optimum doping concentration of 5%, both the reduced Mo⁵⁺ and oxygen vacancies increase, resulting in a decrease in the contact resistivity between the MoO_3−x film and p-type silicon from 161.1 to 62.9 mΩ·cm² and an increase of the effective carrier lifetime from 165.4 to 391.0 μs simultaneously. Similarly, the doping of Ta⁵⁺ or V⁵⁺ in MoO_3−x improves the passivated contact performance with silicon, while the former increases the concentration of oxygen vacancies and the latter reduces it. The solar cell with the structure of Ag/MoO_3−x :Nb/p-Si exhibits a conversion efficiency of 18.37%, which is the highest so far reported for the solution-processed MoO_3−x /silicon heterojunction. This work demonstrates a feasible strategy of tuning hole selectivity in MoO_3−x by doping for high-efficiency solar cells and other optoelectronic device applications.

The pure Dion–Jacobson phase 2D capping layer (n = 1) based on 3-(aminomethyl) piperidinium is demonstrated to form a coordinated energy landscape and homogeneous surface potential distribution at the upper surface of inverted perovskites, effectively reducing the severe interfacial recombination and accelerating the extraction of electrons at the perovskite/PCBM interface before hot-carrier cooling.

Abstract

While quasi-2D perovskite is often used in inverted perovskite solar cells (PSCs) to improve the interfacial carrier transfer, the development of pure 2D perovskite with superior stability is rarely seen and the corresponding carrier-extraction kinetics remains unclear. Here, a variety of hexatomic ring cations including piperidine, pyridine, and cyclohexane are introduced to modify the perovskite/electron transport layer interface. The Dion–Jacobson phase 2D cladding (n = 1) based on 3-(aminomethyl) piperidinium is proved to form a coordinated energy landscape and homogeneous surface potential distribution, and effectively prolong the electron diffusion length (≈1.58 µm) and accelerate the hot-carrier extraction rate (2.5 times that of Control at 400 K). Furthermore, the quasi-2D treatment (n ≈ 3,4) demonstrated a slight escalation in short-circuit current, but failed to inhibit the interdiffusion of Ag, Pb, and I under illumination. Finally, one of the state-of-art power conversion efficiency (PCE) for MA-free inverted PSCs is achieved at 23.62% with increased open-circuit voltage (≈1.15 V) and fill factor (≈82.8%). Most importantly, 89% and 93.6% of initial PCE are retained after 720 h under 85 °C heating and 1000 h under maximum power point tracking, illustrating satisfactory thermal and operational stability with pure 2D perovskite capping layer.

Similar to binary organic solar cells, ternary cells’ quantum efficiency (QE) is controlled by the D/A ionization energy offset (ΔIE) required to overcome the interfacial energy levels bending. Hole transfer occurs though a single channel controlled by the average of ΔIE, weighted for the acceptors ratios. This ratio can thus be adjusted to optimize QE and energy losses.

Abstract

Non-fullerene acceptor (NFA)-based ternary bulk heterojunction solar cells (TSC) are the most efficient organic solar cells (OSCs) today due to their broader absorption and quantum efficiencies (QE) often surpassing those of corresponding binary blends. The impact on QE of the energetics driving charge transfer at the electron donor:electron acceptor (D/A) interfaces is studied in blends of PBDB-T-2F donor with several pairs of lower bandgap NFAs. As in binary blends, the ionization energy offset between donor and acceptor (ΔIE) controls the QE and maximizes for ΔIE > 0.5 eV. However, ΔIE is not controlled by the individual NFAs IEs but by their average, weighted for their blending ratio. Using this property, the QE of a PBDB-T-2F:IEICO binary blend that has an insufficient ΔIE for charge generation is improved by adding a deep IE third component: IT-4F. Combining two NFAs enables to optimize the D/A energy alignment and cells’ QE without molecular engineering.

The Nb₂C MXene, a 2D material, is incorporated into traditional poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS). It effectively facilitates the phase separation of PEDOT and PSS segments, thus enhancing its conductivity and charge extraction ability. This results in a high power convention efficiency (19.33%), which occupies the highest value for single-junction organic solar cells using 2D materials.

Abstract

Niobium-carbide (Nb₂C) MXene as a new 2D material has shown great potential for application in photovoltaics due to its excellent electrical conductivity, large surface area, and superior transmittance. In this work, a novel solution-processable poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)-Nb₂C hybrid hole transport layer (HTL) is developed to enhance the device performance of organic solar cells (OSCs). By optimizing the doping ratio of Nb₂C MXene in PEDOT:PSS, the best power convention efficiency (PCE) of 19.33% can be achieved for OSCs based on the ternary active layer of PM6:BTP-eC9:L8-BO, which is so far the highest value among those of single junction OSCs using 2D materials. It is found that the addition of Nb₂C MXene can facilitate the phase separation of the PEDOT and PSS segments, thus improving the conductivity and work function of PEDOT:PSS. The significantly enhanced device performance can be attributed to the higher hole mobility and charge extraction capability, as well as lower interface recombination probabilities generated by the hybrid HTL. Additionally, the versatility of the hybrid HTL to improve the performance of OSCs based on different nonfullerene acceptors is demonstrated. These results indicate the promising potential of Nb₂C MXene in the development of high-performance OSCs.

By applying longpass filters during photo-aging experiments, the spectral-dependent photostability of Y-series acceptors and solar cells that comprise them is investigated. These tests reveal that high-energy photons are responsible for degradation. Employing device characterization and numerical simulations, solar cell efficiency losses are attributed to trap formation due to photochemical degradation of vinylene groups in Y-series acceptors.

Abstract

Organic photovoltaic cells that employ Y-series non-fullerene acceptors (NFAs) have recently achieved impressive power-conversion efficiencies (>18%). To fulfill their commercial promise, it is important to quantify their operational lifetimes and understand their degradation mechanisms. In this work, the spectral-dependent photostability of films and solar cells comprising several Y-series acceptors and the donor polymer PM6 is investigated systematically. By applying longpass filters during aging, it is shown that UV/near-UV photons are responsible for the photochemical decomposition of Y-series acceptors; this degradation is the primary driver of early solar cell performance losses. Using mass spectrometry, the vinylene linkage between the core and electron-accepting moieties of Y-series acceptors is identified as the weak point susceptible to cleavage under UV-illumination. Employing a series of device characterization, along with numerical simulations, the efficiency losses in organic photovoltaic cells are attributed to the formation of traps, which reduces charge extraction efficiency and facilitates non-radiative recombination as the Y-series acceptors degrade. This study provides new insights for molecular degradation of organic photovoltaic absorber materials and highlights the importance of future molecular design and strategies for improved solar cell stability.

A photostable graphene-like conjugated molecule is developed as the hole-selective contact to improve the operational lifetime of inverted perovskite solar cells, enabling an estimated device operational lifetime of over 3000 h.

Abstract

Further enhancing the operational lifetime of inverted-structure perovskite solar cells (PSCs) is crucial for their commercialization, and the design of hole-selective contacts at the illumination side plays a key role in operational stability. In this work, the self-anchoring benzo[rst]pentaphene (SA-BPP) is developed as a new type of hole-selective contact toward long-term operationally stable inverted PSCs. The SA-BPP molecule with a graphene-like conjugated structure shows a higher photostability and mobility than that of the frequently-used triphenylamine and carbazole-based hole-selective molecules. Besides, the anchoring groups of SA-BPP promote the formation of a large-scale uniform hole contact on ITO substrate and efficiently passivate the perovskite absorbers. Benefiting from these merits, the champion efficiencies of 22.03% for the small-sized cells and 17.08% for 5 × 5 cm² solar modules on an aperture area of 22.4 cm² are achieved based on this SA-BPP contact. Also, the SA-BPP-based device exhibits promising operational stability, with an efficiency retention of 87.4% after 2000 h continuous operation at the maximum power point under simulated 1-sun illumination, which indicates an estimated T ₈₀ lifetime of 3175 h. This novel design concept of hole-selective contacts provides a promising strategy for further improving the PSC stability.

Publication date: 15 March 2023

Source: Joule, Volume 7, Issue 3

Author(s): Shengfan Wu, Ming Liu, Alex K.-Y. Jen