Chen Weijie

The first demonstration of integrating fiber optic sensors into perovskite solar cells (PSCs) to enable real-time and in situ monitoring of the efficiency change process and degradation process of their internal perovskite materials without disrupting PSCs' operation.

Abstract

Understanding the degradation kinetics of perovskite materials in operating perovskite solar cells (PSCs) is critical for developing methods to further enhance their device stability. However, it remains a challenge to capture the details and characteristics of the perovskite degradation process inside operating PSCs under different environmental conditions in real-time at the microscopic scale. Herein, a novel, nondestructive real-time in situ monitoring method based on a tapered seven-core fiber optic sensor is demonstrated. The fiber-optic sensor can be facilely inserted near the surface of the perovskite layer of a working PSCs to monitor its degradation kinetics without interfering with the performance of the device. Stable and reproducible correlations between real-time material degradation and optical wavelength response under different humidity and temperature conditions are observed and quantified. This new measurement tool allows real-time access to the detailed degradation evolution of PSCs, which not only guides the design of more stable devices but also offers the possibility to monitor the health status of PSCs in field applications.

This review discusses the progress of lead-less and lead-free perovskites and establishes the relationship between theoretical calculations, experimental synthesis, and photoelectric applications. Strategies for substituting lead-based perovskites are presented to improve luminescence, adjust emission properties, and enhance stability. Future prospects and challenges for environmentally friendly perovskite materials are also discussed.

Lead-based metal halide perovskite materials have been rapidly developed for light-emitting diodes, solar cells, and photodetectors owing to their excellent optoelectronic properties. Nevertheless, the presence of lead in these materials raises critical concerns regarding their environmental impact and potential toxicity, hindering their commercial development. In response to these concerns, researchers have devoted considerable effort toward the development of environmentally friendly perovskites. In this review, the theoretical evolution path and characteristics of lead-substituted perovskites are first emphasized, as they contribute to the development of high-performance lead-free halide perovskites. Additionally, the current investigation of lead-less and lead-free perovskites including synthesis, optoelectronic properties, and applications is systematic summarized. Notably, the positive effects of both lead-less and lead-free perovskites on structure, optoelectronic properties, and associated devices in comparison to their lead-based counterpart are emphasized. Finally, potential opportunities and challenges for future research into environmentally friendly perovskites and their applications are identified.

Additive and passivator strategy is applied to fabricate wide-bandgap perovskite solar cells with bandgap of 1.68 eV. KSCN is introduced as additive and TEABr is used to passivate perovskite/C₆₀ interface, achieving a open-circuit voltage of 1.22 V. This leads to a power conversion efficiency of 22.02% for the champion device, which is one of the highest efficiencies at this bandgap.

Wide-bandgap (WBG) perovskite solar cells (PSCs) play a crucial role in tandem devices. However, the severe nonradiative recombination that occurs at the interface between perovskite and electron transport layer (ETL) leads to excessive open-circuit voltage (V _OC) loss, which hinders the further improvement of the photovoltaic conversion efficiency (PCE). To mitigate the V _OC loss in WBG PSCs, the defects in grains and grain boundaries are reduced as well as the energy-level alignment between perovskite layer and ETL, so as to improve the carrier collection efficiency, is optimized. Herein, potassium thiocyanate is introduced as an additive and 2-thiophenethylammonium bromide (TEABr) is used to passivate perovskite/C₆₀ interface. The synergistic treatment reduces the defect density and prolongs the carrier lifetime, implying that nonradiative recombination is effectively suppressed. Meanwhile, the energy-level alignment of the perovskite and C₆₀ is optimized, leading to the improvement of V _OC. Finally, WBG PSCs with a bandgap of 1.68 eV achieve a V _OC of 1.22 V (with a V _OC loss of 0.46 V) and a PCE of 22.02%.

The screen-printing technique is apromising fabrication method for making fully-printed perovskite solar cells (PSCs) for industrialization. Here, ionic liquid methylamine propionate with stronger coordination is introduced as a co-solvent to promote the escape of methylamine acetate molecules and the vertical growth of perovskite crystals. Fully screen-printed PSCs yields a champion power conversion efficiency of ≈17%, which is the record value for fully screen-printed PSCs.

Abstract

Using a screen-printing techniques is thought to be a good candidate for simplified, cost-effective, reliable, and scalable fabrication of fully printed perovskite solar cells (PSCs) for industrialization. Nevertheless, the screen-printing of perovskite film has not been realized until recently. This group finished the work using ionic liquid methylamine acetate (MAAc) as pure solvent. However, the space-confining effect during the perovskite crystallization in mesoporous impeded the escape of bottom MAAc molecules, which leads to the poor crystalline quality of the screen-printed film. In this work, ionic liquid methylamine propionate (MAPa) with stronger coordination is introduced as a co-solvent to promote the escape of MAAc molecules by forming the solvent volatilization channels in a confined mesoporous structure, which results in the complete MAAc volatilization and high filling degree of perovskite crystals inside the mesoporous structure. Also, MAPa promotes the vertical growth of perovskite crystals and coordinates with unbonded Pb²⁺ on the perovskite surface, leading to efficient charge transport and interfacial band alignment of the screen-printed film. Finally, fully screen-printed PSCs yields a champion power conversion efficiency (PCE) of ≈17%, which is the record value for fully screen-printed PSCs. Moreover, the unencapsulated device shows robust operational stability that maintains >85.3% of initial PCE (25%RH and 25 °C) under continuous illumination at the maximum power point after 250 h.

Organic Photovoltaic (OPV) is a promising technology for converting artificial light into electrical power for IoT devices. OPVs can achieve high efficiencies under indoor illumination using white light-emitting diode (LED) light. However, they often suffer from poor stability under full sunlight compared to inorganic PV technologies. This study shows that organic solar cells and modules can achieve remarkable stabilities under typical indoor illumination.

Abstract

Organic Photovoltaics (OPV) is a very promising technology to harvest artificial illumination and power smart devices of the Internet of Things (IoT). Efficiencies as high as 30.2% have been reported for OPVs under warm white light-emitting diode (LED) light. This is due to the narrow spectrum of indoor light, which leads to an optimal bandgap of ≈1.9 eV. Under full sunlight, OPV devices often suffer from poor stability compared to the established inorganic PV technologies such as crystalline silicon. This study focuses on a potentially very cost-effective Indium Tin Oxide (ITO) free cell stack with absorber materials processed from non-halogenated solvents. These organic solar cells and modules with efficiencies up to 21% can already achieve remarkable stabilities under typical indoor illumination. Aging under 50,000 lux LED lighting leads to very little degradation after more than 11 000 h. This light dose corresponds to more than 110 years under 500 lux. For modules encapsulated with a flexible barrier, extrapolated lifetimes of more than 41 years are achieved. This shows that OPV is mature for the specific application under indoor illumination. Due to the large number of potential organic semiconducting materials, further efficiency increase can be expected.

2D material of graphene is first employed to passivate the detrimental grain boundaries (GBs) of polycrystalline CZTSSe film. The graphene distributed at the GBs can effectively mediate carrier transport, promote the conductivity, and thus extend minority carrier lifetime of the absorber. This work provides a brand-new strategy to modify the GBs and decrease carrier loss for polycrystalline optoelectronic device.

Abstract

Grain boundaries (GBs)-triggered severe non-radiative recombination is recently recognized as the main culprits for carrier loss in polycrystalline kesterite photovoltaic devices. Accordingly, further optimization of kesterite-based thin film solar cells critically depends on passivating the grain interfaces of polycrystalline Cu₂ZnSn(S,Se)₄ (CZTSSe) thin films. Herein, 2D material of graphene is first chosen as a passivator to improve the detrimental GBs. By adding graphene dispersion to the CZTSSe precursor solution, single-layer graphene is successfully introduced into the GBs of CZTSSe absorber. Due to the high carrier mobility and electrical conductivity of graphene, GBs in the CZTSSe films are transforming into electrically benign and do not act as high recombination sites for carrier. Consequently, benefitting from the significant passivation effect of GBs, the use of 0.05 wt% graphene additives increases the efficiency of CZTSSe solar cells from 10.40% to 12.90%, one of the highest for this type of cells. These results demonstrate a new route to further increase kesterite-based solar cell efficiency by additive engineering.

A novel in situ combined dual-hole transport layer with 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pn) is introduced to enhance the performance in Spiro-OMeTAD-based PSCs. This approach improves hole extraction, reduces non-radiative recombination, and increases PCE from 22.42% to 24.13%. The method also enhances stability, resulting in a 44% improvement in thermal stability, presenting a valuable strategy for optoelectronic devices.

Abstract

Spiro-OMeTAD is a commonly used material in perovskite solar cells (PSCs). It requires chemical doping with a lithium compound and 4-tert-butylpyridine to enhance its conductivity and hole extraction efficiency. However, this conventional doping process has limitations in terms of efficiency and stability. In this study, an innovative approach using an in situ combined dual-hole transport layer with 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pn) is introduced to improve PSC performance. These results show that this in situ combined hole transport layer with TIPS-Pn channels effectively extracts and transports hole carriers, reducing non-radiative recombination. Additionally, it allows for the absorption of excess photo energy from hot hole carriers, resulting in a significant increase in the average power conversion efficiency of PSCs from 22.42% to 24.13%. Furthermore, the device retains 90% of its initial efficiency after 1900 h of exposure to air, indicating improved stability. Notably, a 44% improvement in thermal stability is observed after 500 h due to the robust morphology and hydrophobic surface. This work presents a novel strategy for enhancing the performance of Spiro-OMeTAD in PSCs and provides valuable insights into hole carrier dynamics in perovskite-based optoelectronic devices.

The abundant oxygen-related defects seriously impair the photovoltaic performance and stability of perovskite solar cells. Here, a novel surface energy engineering (SEE) is developed by applying a surfactant HFSTA on the surface of the TiO₂ substrate. By combining the passivation of TiO₂, crystallization process modulation and stress relief, PCE of 25.03% is achieved on champion device along with improved stability.

Abstract

The abundant oxygen-related defects (e.g., O vacancies, O–H) in the TiO₂ electron transport layer results in high surface energy, which is detrimental to effective carrier extraction and seriously impairs the photovoltaic performance and stability of perovskite solar cells. Here, novel surface energy engineering (SEE) is developed by applying a surfactant of heptadecafluorooctanesulfonate tetraethylammonium (HFSTA) on the surface of the TiO₂. Theoretical calculations show that the HFSTA-TiO₂ is less prone to form O vacancies, leading to lower surface energy, thus improving the carrier-extraction efficiency. The experimental results show that superior perovskite film is obtained due to the reduced heterogeneous nucleation sites and improved crystallization process on the modified TiO₂. Furthermore, the flexible long alkyl chains in HFSTA considerably relieve the compressive stresses at the buried interface. By combining the passivation of TiO₂, crystallization process modulation, and stress relief, a champion PCE up to 25.03% is achieved. The device without encapsulation sustains 92.2% of its initial PCE after more than 2500 h storage under air ambient with relative humidity of 25–30%. The SEE of a buried interface paves a new way toward high-efficiency, stable perovskite solar cells.

Publication date: 15 December 2023

Source: Nano Energy, Volume 118, Part B

Author(s): Qi Zhang, Qiangqiang Zhao, Chenyang Zhang, Caidong Cheng, Kai Wang

Interlayer molecules functionalized with different side groups are rationally designed to investigate the correlation between defect-passivation strength and interfacial carrier dynamics. The incorporation of carbonyl as the side group simultaneously promotes the carrier-collection yield as well as sufficient defect passivation, leading to a champion power conversion efficiency of 23.25%.

Abstract

Considering the high surface defects of polycrystalline perovskite, chemical passivation is effective in reducing defects-associated carrier losses. However, challenges remain in promoting passivation effects without compromising the carrier-extraction yield at the perovskite interfaces. In this work, interlayer molecules functionalized with different side groups are rationally designed to investigate the correlation between defect-passivation strength and interfacial carrier dynamics.  It is revealed that Cl-grafted molecules impose destructive effects on the perovskite structure due to its lower electronegativity and mismatched spatial configuration. The introduction of cyanide (CN) as a side group in molecules also leads to perovskite deformation and unfavorable hole collection. After the molecular optimization, the incorporation of carbonyl (C═O) as the side group (TPA─O) simultaneously promotes the carrier-collection yield as well as sufficient defect passivation. As a consequence, the devices based on TPA─O yield a champion PCE of 23.25%, along with remarkable stability by remaining above 88.5% of initial performance after 2544 h storage in the air. Furthermore, this interlayer based on TAP─O enables flexible devices to achieve a high efficiency of 21.81% and promising mechanical stability. This work paves the way for further improving the performance of perovskite solar cells.

By constructing a variety of luminescent charge-transfer (CT) cocrystals applying brominated pyromellitic dianhydride (PMDA) as an π-electron acceptor, homogeneous and heterogeneous assemblies based on these PMDA-based CT complexes are both achieved, giving rise to alloyed and heterostructured microcrystals. Ternary alloyed CT microcrystals display composition-dependent optical waveguiding abilities, while An-PMDA@Ph-PMDA core-shell microrods present wavelength-dependent two-photon excited fluorescence performances.

Abstract

Using easily hydrolyzable brominated pyromellitic dianhydride (PMDA) as an electron acceptor, a wide variety of structurally stable binary organic charge-transfer (CT) microcrystals that are stabilized by dominant intermolecular CT interactions is achieved. By varying the electron-donating abilities of π-electron compounds, the resulting single crystalline CT assemblies display tailorable fluorescence emissions spanning from green to near-infrared. Upon implantation of a π-electron donor anthracene (An) into fluoranthene-PMDA (Fl-PMDA), red and NIR emissions of ternary alloyed assemblies are substantially enhanced due to efficient energy transfer from Fl-PMDA to An-PMDA as well as structural complementarity between two CT complexes. Depending on the well-matched epitaxial relationship, seeded growth of phenanthrene-PMDA (Ph-PMDA) onto the pre-existing An-PMDA microcrystals is also achieved, leading to core-shell heterostructures with full and partial coverage. Such an epitaxial growth strategy is also applicable to the construction of microscale heterostructures of diverse CT complex combinations. The ternary Fl_{1− x} An _x -PMDA alloyed assemblies display composition-dependent tailorable optical waveguiding behaviors. While An-PMDA@Ph-PMDA core-shell microrods present wavelength-dependent two-photon excited fluorescence performances. The rational creation of these homogeneous and heterogeneous CT-assembled architectures provides us a deep insight to investigate multicomponent functional organic cocrystals.

A novel ligand cystamine (CYS) is introduced to construct low-dimensional Dion-Jacobson perovskite, which achieves excellent charge transport and low exciton binding energy. The (CYS)(MA)₄Pb₅I₁₆ film shows diminished defect densities and heightened light responsivity, leading to the CYS-based perovskite solar cells achieving a champion efficiency of 16.52% with significant stability.

Abstract

Low-dimensional (LD) perovskite has provided an exciting avenue for exploring stable perovskite solar cells (PSCs). However, PSCs based on LD perovskites still suffer from poor efficiency owing to unfavorable charge carrier dynamics. Here, cystamine (CYS) is employed as a ligand to construct LD Dion-Jacobson (LDDJ) perovskite (CYS)MA_n-1Pb_nI_3n+1 (n = 1, 2, 3…, MA: methylamine) for improving carrier properties. The disulfide bond not only changes the polarization characteristic but also increases the coupling between inorganic slabs due to the low barrier of rotation around the S-S axis, thus reducing the exciton binding energy of CYS-based LDDJ perovskite. Disulfide bonds provide a scene for charge localization in the interlayer region, which is conducive to reducing the anisotropy of charge transfer. Thanks to these merits, the (CYS)MA₄Pb₅I₁₆ film delivers improved carrier diffusion length (electron for 1345 nm and hole for 950 nm) and mobility (9.23 cm² V⁻¹ S⁻¹). As a result, the (CYS)(MA)₄Pb₅I₁₆ PSC achieves a champion power conversion efficiency (PCE) of 16.52%, which is much higher than that of HDA and BA cations-based PSCs (HDA: 1,6-Hexanediamine, BA: Butylamine). Furthermore, the state-of-the-art device only lost 8% of its initial PCE after 1600 h in the atmosphere.

The 2-decyl[1]benzothieno [3,2-b][1]benzothiophene (C10-BTBT) is a small molecule p-type semiconductor. In p–i–n perovskite (E _g = 1.64 eV) solar cell, C10-BTBT deposited on top of (2-(3,6-dimethoxy-9H-carbazol-9-yl) ethyl) phosphonic acid self-assembling monolayer exhibits cofacial interaction. This enhances the charge transfer at the interface yet preserving the desirable property of hole-transporting layer and perovskite resulting in a very high fill factor of 85.89% and an improved efficiency.

Perovskite solar cells (PSCs) have received considerable attention for their increasing photovoltaic performance achieved through fine optimization of stacking layers and experimentation with device architecture. The incorporation of interlayers is shown to positively impact the fabrication process by improving photovoltaic parameters. In recent years, carbazole-based self-assembled monolayers (SAMs) are investigated as a potential hole-transport layer (HTL), due to their efficient passivating nature at the hole-selective interface and faster charge extraction. In this study, a novel interlayer 2-decyl[1]benzothieno [3,2-b][1]benzothiophene (C10-BTBT) is introduced, over the HTL SAM (2-(3,6-dimethoxy-9H-carbazol-9-yl) ethyl) phosphonic acid, also known as MeO–2PACz. This new interlayer over SAMs significantly improves charge transfer at the interface, resulting in a high fill factor of 85.89% and a boost in power conversion efficiency from 18.04% to 20.50%. In this research, the potential of interlayer–SAM combinations is highlighted in advancing PSC technology.

Nature Energy, Published online: 19 October 2023; doi:10.1038/s41560-023-01377-7

An advancement in quantum dot (QD) surface passivation by introducing multifunctional ligands glycocyamine (GLA) to the formamidinium lead iodide QD surface is demonstrated. The use of GLA ligands replaces the native long-chain surface ligands, modulates the population of QD domains, and shifts the band offsets of the QD films, achieving a high-record power conversion efficiency of 15.34%.

Abstract

Formamidinium lead iodide quantum dots (QDs) show great potential for solar cell applications but suffer from restricted charge transfer due to the insulating nature of their ligand shell. Management of the surface properties and resultant energy band alignment is the key to efficient and stable QD solar cells. Herein, an advance in QD surface passivation by introducing tailored multifunctional ligands (glycocyamine (GLA)) to the FAPbI₃ QD surface is demonstrated. The incorporation of GLA ligands can partly substitute the native long-chain insulating ligands and effectively reduce the non-radiative recombination loss induced by surface trap states. Notably, the introduction of GLA ligands beneficially shifts the band offsets of the QD films and generates a homojunction structure with a cascading energy band alignment in the QD layers, promoting favorable charge transport and boosting the device's performance. As a result, a record-high power conversion efficiency (PCE) of 15.34% with improved open-circuit voltage and fill factor is achieved. Moreover, the GLA-assisted surface passivation boosts the device stability, in which over 80% and 75% of the original PCEs are maintained after storing the devices for 5500 h in ambient air and 768 h under continuous 1-sun illumination, respectively.

The ionic-liquid 1,3-dimethylimidazolium methanesulfonate with high ionic conductivity and excellent thermal stability is introduced for methylammonium-free perovskite solar cells via smoothed-interface engineering. This results in efficient solar cells with power conversion efficiency of 23.91% as well as demonstrated air stability, which is mainly attributed to the effective interfacial passivation and the optimized energy-level alignment.

A judicious modification of the buried interface can enhance the quality of perovskite films and reduce non-radiative recombination losses, particularly in methylammonium (MA)-free perovskite solar cells (PSCs). In this study, the ionic-liquid 1,3-dimethylimidazolium methanesulfonate (DMIMMeSO₄) is employed, characterized by its high ionic conductivity and excellent thermal stability, to regulate the perovskite/SnO₂ interface. The nitrogen component in DMIMMeSO₄ can interact with Sn⁴⁺ through Lewis acid–base interactions, effectively passivating defects associated with tin and suppressing the formation of oxygen vacancies, leading to reduced non-radiative recombination of charge carriers. In addition, [MeSO₄]⁻ can also form coordination bonds with PbI₂, creating a better perovskite film with smoothed interface. Moreover, DMIMMeSO₄ also optimize the energy-level alignment, thereby reducing the charge-transfer barrier and enhancing charge-extraction efficiency. As a result, power conversion efficiency of 23.91% is achieved by MA-free PSCs modified with DMIMMeSO₄. Furthermore, after 1000 h of ambient air storage, devices that are not encapsulated maintaine over 90% efficiency. In all of these results, it is clearly indicated that interface modulation based on ionic-liquid-assisted smoothed-interface engineering is an effective approach for obtaining high-performance PSCs.

Crown ether dibenzo-21-crown-7 is employed in wide-bandgap perovskite solar cells based on MAPbBr₃. This results in the open-circuit voltage up to 1.5 V with competitive solar cell performances and enhanced operational stabilities under elevated temperatures, highlighting the versatility of host–guest complexation in wide-bandgap materials and solar cells.

Wide-bandgap hybrid halide perovskites are increasingly relevant in the fabrication of tandem solar cells. However, their efficiency and stability during operation are still limited by several factors, among which ion migration at the interface with charge-selective extraction layers is one of the most detrimental ones. Herein, a host–guest complexation strategy is employed to control interfacial ion migration by using dibenzo-21-crown-7 in wide-bandgap hybrid halide perovskites based on methylammonium lead bromide. The capacity of the crown ether is demonstrated that affect the performances and stabilities of MAPbBr₃ solar cells. As a result, power conversion efficiencies of up to 5.9% are achieved with an open circuit voltage as high as 1.5 V, which is accompanied by stability over 300 h at 85 °C under nitrogen atmosphere, as well as more than 300 h at ambient temperature, maintaining ∼80% of initial performance. This provides a versatile strategy for wide-bandgap photovoltaic devices.

While heterojunctions with intermixed or gradient perovskites can reduce surface recombination, the aggregation and phase distribution of 2D perovskite induce transport losses, thereby limiting device fill factors. Accordingly, bulk in situ reconstruction (BISR) strategy is proposed to induce the reconstruction of 3D perovskites on a minim self-assembled 2D crystal seed, forming heterojunction perovskite that runs through the entire active layer.

Abstract

Heterojunction perovskite solar cells combine the stability of 2D perovskites and the high efficiency of 3D perovskites, making them an excellent photovoltaic candidate. While heterojunctions with intermixed or gradient perovskites can reduce surface recombination, the aggregation and phase distribution of 2D perovskite induce transport losses, thereby limiting device fill factors. Accordingly, a bulk in situ reconstruction (BISR) strategy is proposed to induce the reconstruction of 3D perovskites on a minim self-assembled 2D crystal seed, forming heterojunction perovskite that runs through the entire active layer. This facilitates charge extraction, relieves tensile stress, and avoids the decomposition of perovskite on grain boundaries. As a result, the best-performing heterojunction perovskite solar cells show a high-power conversion efficiency (PCE) of 24.06% with 82.9% FF for the small-area device (0.105 cm²) and a superior PCE of 19.2% for the large-area module (5 × 5 cm²). Importantly, the unencapsulated device shows dramatically improved operational stability, maintaining 87% of its initial efficiency after 8000 h of storage under ambient atmosphere at room temperature. This work provides an effective and simple approach to establish heterojunction perovskite to simultaneously boost the efficiency and stability of PSCs.

Publication date: 1 December 2023

Source: Electrochimica Acta, Volume 470

Author(s): Tong Tong, Daize Mo, Kuirong Deng

SnO₂ nanoparticles are a promising   electron transport material for solar cells. However, in the case of organic solar cells, the formation of defective interfaces leads to non-ideal device characteristics and poor stability. This problem is tackled by studying their surface chemistry and a simple method is proposed that vastly increases the efficiency and the lifetime of the devices.

Abstract

In organic solar cells, the interfaces between the photoactive layer and the transport layers are critical in determining not only the efficiency but also their stability. When solution-processed metal oxides are employed as the electron transport layer, the presence of surface defects can downgrade the charge extraction, lowering the photovoltaic parameters. Thus, understanding the origin of these defects is essential to prevent their detrimental effects. Herein, it is shown that a widely reported and commercially available colloidal SnO₂ dispersion leads to suboptimal interfaces with the organic layer, as evidenced by the s-shaped J–V curves and poor stability. By investigating the SnO₂ surface chemistry, the presence of potassium ions as stabilizing ligands is identified. By removing them with a simple washing with deionized water, the s-shape is removed and the short-circuit current is improved. It is tested for two prototypical blends, TPD-3F:IT-4F and PM6:L8:BO, and for both the power conversion efficiency is improved up to 12.82% and 16.26%, from 11.06% and 15.17% obtained with the pristine SnO₂, respectively. More strikingly, the stability is strongly correlated with the surface ions concentration, and these improved devices maintain ≈87% and ≈85% of their initial efficiency after 100 h of illumination for TPD-3F:IT-4F and PM6:L8:BO, respectively.

The chloro-assisted chelating hole transporting material (HTM) based on a triarylamine core for inverted perovskite solar cells and with the unique chelating interaction is demonstrated. The best interface contact and lowest trap density are obtained resulting in the best device performance.

Abstract

Hole-transporting materials (HTMs) play an important role in transporting photogenerated holes, tuning the perovskite crystallization process, and passivating uncoordinated Pb²⁺ defects for high-performance inverted perovskite solar cells (PSCs). Herein, a unique cost-effective small molecule-type HTM based on a triarylamine core bearing a chloro-assisted chelating moiety (named TPA-CAA) is synthesized, which has excellent affinity to the perovskite precursor solution leading to smooth and uniform perovskite films. In comparison with the structurally similar molecule TPA-AA with the absence of the chloro-substituent, TPA-CAA can form a chelate structure with Pb²⁺ via the carbonyl and the adjacent chloro-atom, which efficiently tunes the perovskite crystallization, passivates the defects, and enhances the hole transporting at the perovskite/HTL interface. Eventually, the TPA-CAA-based inverted PSC achieves a champion power conversion efficiency (PCE) of 21.56% (19.64% and 18.84% for the poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) and TPA-AA ones, respectively) with a high open-circuit voltage (V _OC) of 1.113 V. Moreover, the stability of the TPA-CAA-based device is notably improved, and the PCE maintains over 80% of its initial value over 1000 h storage in ambient air (25 °C, relative humidity 30–40%) without encapsulation, in comparison to that of the PTAA device (only 50% of the initial value left over 1000 h).

Functionalized 2D Ti₃C₂ MXene thin films are employed as transport layers in perovskite solar cells, resulting in devices with efficiencies above ≈22 %. Outstanding indoor and outdoor stability performance is observed and attributed to the passivation of shallow and deep defects.

Abstract

Despite the performance improvement in perovskite solar cells (PSCs) when MXenes are employed as transport layers, device stability studies are still missing. Especially under real outdoor conditions where devices are subjected to the synergy of multiple stressors. In this work, functionalized 2D titanium carbide (Ti₃C₂) MXene is employed in normal PSC configuration, at the interface between the halide perovskite and the hole transport layer. The functionalization of the Ti₃C₂ MXene is made utilizing the same organic additive passivating the halide perovskite layer. The functionalizing strategy creates a continuous link between the MXene and the halide perovskite layer. Champion MXene-based PSCs revealed a ≈22% efficiency, in comparison with the control device showing 20.56%. Stability analyses under ISOS protocols under different conditions (dark, continuous light irradiation and real outdoor analysis) reveal that the enhancement of the PSCs lifespan is always observed when the MXene layer is employed. Analysis under continuous light irradaition (ISOS-L) reveal an almost 100% retention of the efficiency for the MXene-modified device, and outdoor testing (ISOS-O) carried out for > 600 h reveals a T₈₀ of ≈600 h, while the control device degrades completely. To the best of the authors' knowledge, this is the first report of the stability assesment of MXene-based PSCs carried out under real outdoor (ISOS-O) conditions.

Publication date: 15 December 2023

Source: Nano Energy, Volume 118, Part B

Author(s): Xin Li, Sikandar Aftab, Aumber Abbas, Sajjad Hussain, Muhammad Aslam, Fahmid Kabir, Hisham S.M. Abd-Rabboh, H.H. Hegazy, Fan Xu, Mohd Zahid Ansari

Publication date: 15 December 2023

Source: Nano Energy, Volume 118, Part B

Author(s): Yiwu Zhu, Xiangyu Shen, Hanjian Lai, Mingrui Pu, Yulin Zhu, Xue Lai, Shilong Xiong, Feng He

Publication date: 15 December 2023

Source: Nano Energy, Volume 118, Part B

Author(s): Congcong Liu, Haijun Su, Yu Pu, Min Guo, Peng Zhai, Zhike Liu, Zhuo Zhang

A record efficiency of 15.8% is achieved for organic solar cells with an area of ≥1 cm² using D18:Y6 as absorber material. The optimized layer stack features a custom antireflection coating (ARC) optimized for the absorption profile of the photoactive material. The ARC shows excellent performance in comparison to bare glass itself and glass coated with other commonly used ARCs.

Organic solar cells are on the verge of reaching 20% power conversion efficiency (PCE) on small device areas (< 0.1 cm²). Herein, an improved efficiency of organic solar cells based on the donor polymer D18 combined with the non-fullerene acceptor Y6 with an active area of ≥1 cm² reaching a certified PCE of 15.8% is reported. This is achieved due to an increase in photogenerated current enabled by a fully magnetron sputtered multilayer antireflection coating (ARC) custom designed for the absorption profile of the photoactive layer. The influence of this ARC in the visible to near infrared range is quantified by means of full optical device simulations predicting a photogenerated current gain of 3.9%. With the advanced device architecture, the best solar cell is measured independently by Fraunhofer ISE calibration lab obtaining the following values: open-circuit voltage = 851.3 mV, short-circuit current density = 25.11  mA cm⁻², fill factor = 73.89% on an active area of 1.0645 cm² thus yielding the improved world record efficiency in the category of cell areas ≥1 cm².