Chen Weijie

In this work, thioacetamide (TA) is selected as a sulfur-containing additive for the precursor solution used in the hydrothermal deposition of Sb₂(S,Se)₃. With the incorporation of TA, the formation of large voids within the Sb₂(S,Se)₃ absorber is suppressed, and deep-level donor-like defects such as sulfur vacancies are passivated, resulting in enhanced performance of Sb₂(S,Se)₃ solar cells.

Abstract

Antimony selenosulfide (Sb₂(S,Se)₃) has recently emerged as a promising light-absorbing material, attributed to its tunable photovoltaic properties, low toxicity, and robust environmental stability. However, despite these advantages, the current record efficiency for Sb₂(S,Se)₃ solar cells significantly lags behind their Shockley–Queisser limit, especially when compared to other well-established chalcogenide-based thin-film solar cells, such as CdTe and Cu(In,Ga)Se₂. This underperformance primarily arises from the formation of unfavorable defects, predominately located at deep energy levels, which act as recombination centers, thereby limiting the potential for performance enhancement in Sb₂(S,Se)₃ solar cells. Specifically, deep-level defects, such as sulfur vacancy (V_S), have a lower formation energy, leading to severe non-radiative recombination and compromising device performance. To address this challenge, thioacetamide (TA), a sulfur-containing additive is introduced, into the precursor solution for the hydrothermal deposition of Sb₂(S,Se)₃. This results indicate that the incorporation of TA helps in passivating deep-level defects such as sulfur vacancies and in suppressing the formation of large voids within the Sb₂(S,Se)₃ absorber. Consequently, Sb₂(S,Se)₃ solar cells, with reduced carrier recombination and improved film quality, achieved a power conversion efficiency of 9.04%, with notable improvements in open-circuit voltage and fill factor. This work provides deeper insights into the passivation of deep-level donor-like V_S defects through the incorporation of a sulfur-containing additive, highlighting pathways to enhance the photovoltaic performance of Sb₂(S,Se)₃ solar cells.

Multifunctional Lewis base additive thionicotinamide (TNM) improves lead halide perovskite solar cell performance by synergistically passivating the antisite lead (Pb) defects and reducing nonradiative recombination. The passivation effect of TNM enhances grain size and crystallinity, leading to fewer grain boundaries and trap states, resulting in charge-transport improvements and boosting efficiency from 16.86% to 19.26%.

Defect passivation inside the crystal lattice and the grain-boundary (GB) surface of the perovskite films has become the most effective strategy to suppress the negative impact of the nonradiative recombination in perovskite solar cell. In this study, a unique approach to effectively passivate the defect states of MAPbI₃ perovskite thin film using thionicotinamide (TNM) as a multifunctional Lewis base additive is demonstrated. TNM as an additive with three different types of Lewis base sites, i.e., pyridine, amino, and CS functional groups, is introduced to mitigate the trap states in the TNM-modified perovskite films and thoroughly investigate the passivation defects. The nonbonded electron of the three different Lewis base sites can synergistically passivate the antisite lead (Pb) defects and improve the stability of the device. In addition, the NH₂ group can form ionic bonds with negatively charged I– ions and inhibit ion migration caused by them. It is found that such passivation effect of TNM reduces the GB defects and improves the crystallinity significantly. As a result, a champion TNM-modified device shows an improved power conversion efficiency of 19.26% from 16.86% along with enhanced open-circuit voltage, fill factor, and negligible hysteresis.

A diffusion-regulated ternary structure containing two narrow-bandgap non-fullerene acceptors enhances the absorption in the near-infrared region. By integration with wide-bandgap perovskite front subcells, a power conversion efficiency of 24.5% is achieved in perovskite/organic tandem solar cells.

Abstract

The compatibility of perovskite and organic photovoltaic materials in solution processing provides a significant advantage in the fabrication of high-efficiency perovskite/organic tandem solar cells. However, additional recombination losses can occur during exciton dissociation in organic materials, leading to energy losses in the near-infrared region of tandem devices. Consequently, a ternary organic rear subcell is designed containing two narrow-bandgap non-fullerene acceptors to enhance the absorption of near-infrared light. Simultaneously, a unique diffusion-controlled growth technique is adopted to optimize the morphology of the ternary active layer, thereby improving exciton dissociation efficiency. This innovation not only broadens the absorption range of near-infrared light but also facilitates the generation and effective dissociation of excitons. Owing to these technological improvements, the power conversion efficiency (PCE) of organic solar cells increased to 19.2%. Furthermore, a wide-bandgap perovskite front subcell is integrated with a narrow-bandgap organic rear subcell to develop a perovskite/organic tandem solar cell. Owing to the reduction in near-infrared energy loss, the PCE of this tandem device significantly improved, reaching 24.5%.

An effective asymmetric π-extended self-assembled monolayer (A-4PADCB) is designed and synthesized, demonstrating favorable coverage on ITO and optimized interface contact with perovskite. When applied A-4PADCB as buried substrate, the power conversion efficiencies (PCEs) of 25.05% for flexible perovskite solar cells and 20.64% (certified 19.51%) for flexible perovskite solar modules are obtained, which are the highest PCEs in the reported literature.

Abstract

Flexible perovskite solar cells (f-PSCs) have emerged as potential candidates for specific mechanical applications owing to their high foldability, efficiency, and portability. However, the power conversion efficiency (PCE) of f-PSC remains limited by the inferior contact between perovskite and flexible buried substrate. Here, an asymmetric π-extended self-assembled monolayer (SAM) (4-(9H-dibenzo[a,c]carbazol-9-yl)butyl)phosphonic acid (A-4PADCB) is reported as a buried substrate for efficient inverted f-PSCs. Employing this design strategy, A-4PADCB exhibits a significant orientation angle away from the surface normal, homogenizing the distribution of contact potentials. This enhancement improves the SAM/perovskite interface quality, controlling the growth of favorable perovskite films with low defect density and slight tensile stress. Integration of A-4PADCB into small-area f-PSCs and large-area flexible perovskite solar modules with an aperture area of 20.84 cm² achieves impressive PCEs of up to 25.05% and 20.64% (certified 19.51%), respectively. Moreover, these optimized A-4PADCB-based f-PSCs possess enhanced light, thermal, and mechanical stability. This research paves a promising avenue toward the design of SAM-buried substrates with a large orientation angle, regulating perovskite growth, and promoting the commercialization of large-area flexible perovskite photovoltaics.

In this study, Au nanoparticle-based plasmonic metasurface shows promising potential to fine control the phase segregation and photoluminescence in mixed halide perovskite thin films. By tuning the hot-electron coupling efficiency, localized control and gate tunable phase segregation are achieved, illustrating the prosperous perspective of perovskite-based hot-electron optoelectronics.

Abstract

The rapid development of mixed-halide perovskites has established a versatile optoelectronic platform owing to their extraordinary physical properties, but there remain challenges toward achieving highly reliable synthesis and performance, in addition, post-synthesis approaches for tuning their photoluminescence properties after device fabrication remain limited. In this work, an effective approach is reported to leveraging hot electrons generated from plasmonic nanostructures to regulate the optical properties of perovskites. A plasmonic metasurface composed of Au nanoparticles can effectively tailor both photoluminescence and location-specific phase segregation of mixed-halide CsPbI₂Br thin films. The ultrafast transient absorption spectroscopy measurements reveal hot electron injection on the timescale of hundreds of femtoseconds. Photocurrent measurements confirm the hot-electron-enhanced photon-carrier conversion, and in addition, gate-voltage tuning of phase segregation is observed because of correlated carrier injection and halide migration in the perovskite films. Finally, the characteristics of the gate-modulated light emission are found to conform to a rectified linear unit function, serving as nonlinear electrical-to-optical converters in artificial neural networks. Overall, the hot electron engineering approach demonstrated in this work provides effective location-specific control of the phase and optical properties of halide perovskites, underscoring the potential of plasmonic metasurfaces for advancing perovskite technologies.

In this work, a photothermal welding method is used to weld the grain boundaries after NIR laser treatment by applying NIR dye (indocyanine green, ICG) and polymer (polycaprolactone, PCL) as additives, improving the brittle grain boundaries and defects of flexible perovskite films. The optimized ICG/PCL-doped PSCs achieve superior PCE of 20.62% and 19.55% for rigid and flexible devices, respectively.

Abstract

Flexible perovskite solar cells (f-PSCs) have drawn widespread interest owing to their distinguished advantages in excellent flexibility and relatively low cost. However, the brittle grain boundaries (GBs) and defects in flexible perovskite film tremendously influence the power conversion efficiency (PCE) and mechanical flexibility of f-PSCs. Herein, photothermal welding, a novel method, is used to improve the perovskite films quality and the PCE of f-PSCs with a near-infrared (NIR) dye (indocyanine green, ICG) and polycaprolactone (PCL) as additives. Due to the strong photothermal effect, ICG molecule not only can significantly enhance NIR light harvesting, but it also can weld GBs upon exposure to an NIR laser, which is conducive to the GBs connections and device flexibility. Meanwhile, the S═O bond of ICG and C═O bond of PCL can simultaneously coordinate with Pb²⁺ defects in perovskite. Furthermore, they can control crystal growth to form a smooth surface of perovskite film. Consequently, the unencapsulated PSCs based on ICG/PCL displays a high champion PCE of 20.62%, with 88.4% of the original PCE after being placed in dark conditions for 600 h. The f-PSCs delivers a champion PCE of 19.55% and exhibits excellent mechanical stability, thus providing a meaningful scientific direction to fabricate high-flexible f-PSCs.

We first reveal the unknown relation between ion migration and crystal facet, in which the (100) facet is substantially more vulnerable to occur cationic migration than the (111) facet, and then control the (111)-orientation through an antisolvent strategy. The PSCs with (111)-dominated perovskite achieve a PCE of 26.0 % (25.4 % certification), and can maintain >95 % of their initial PCEs after 3500-hours operation under 1-sun illumination.

Abstract

Ion migration is a major issue hindering the long-term stability of perovskite solar cells (PSCs). As an intrinsic characteristic of metal halide perovskite materials, ion migration is closely related to the atomic arrangement and coordination, which are the basic characteristic differences among various facets. Herein, we report the facet-related ion migration, and then achieve the inhibition of ion migration in perovskite through finely modulating the facet orientation. We show that the (100) facet is substantially more vulnerable to cationic migration than the (111) facet. The main reason for this difference in migration is that the cationic migration route in the (111) facet deviates from that in the (100) facet, which increases the active migration energy and weakens the contribution from the electric field during operation. We prepare a (111)-dominated perovskite film by incorporating a facile and green addition of water (H₂O) into the antisolvent, further achieving a power conversion efficiency (PCE) of 26.0 % (25.4 % certification) on regular planar PSCs and 25.8 % on inverted PSCs. Moreover, the unencapsulated PSCs can maintain 95 % of their initial PCE after 3500-hours operation under simulated AM1.5 illumination at the maximum power point.

Nature Photonics, Published online: 18 September 2024; doi:10.1038/s41566-024-01531-x

A dual modification approach involving AlO_x and F-doped phenyltrimethylammonium bromide (F-PTABr) layers is employed to improve the buried interface contact and perovskite crystallization process during vapor–solid reaction. As a result, perovskite solar cells exhibit a impressive improvement in power conversion efficiency from 19.48% of the reference device to 21.53% of the modified devices.

Abstract

Vapor-deposited inverted perovskite solar cells utilizing self-assembled monolayer (SAM) as hole transport material have gained significant attention for their high efficiencies and compatibility with silicon/perovskite monolithic tandem devices. However, as a small molecule, the SAM layer suffers low thermal tolerance in comparison with other metal oxide or polymers, rendering poor efficiency in solar device with high-temperature (> 160 °C) fabricating procedures. In this study, a dual modification approach involving AlO_x and F-doped phenyltrimethylammonium bromide (F-PTABr) layers is introduced to enhance the buried interface. The AlO_x dielectric layer improves the interface contact and prevents the upward diffusion of SAM molecules during the vapor–solid reaction at 170 °C, while the F-PTABr layer regulates crystal growth and reduces the interfacial defects. As a result, the AlO_x/F-PTABr-treated perovskite film exhibits a homogeneous, pinhole-free morphology with improved crystal quality compared to the control films. This leads to a champion power conversion efficiency of 21.53% for the inverted perovskite solar cells. Moreover, the encapsulated devices maintained 90% of the initial efficiency after 600 h of ageing at 85 °C in air, demonstrating promising potential for silicon/perovskite tandem application.

Tin oxide is a widely employed charge-transport material for high-performance perovskite solar cells. In this work, a graded redox interfacial modifier, cobalt hexammine sulfamate, is found to improve the properties of tin oxide. It reduces the interfacial defect density and improving the crystallinity of the perovskite. The resultant perovskite solar cells show excellent stability under elevated temperatures.

Abstract

Perovskite solar cells have emerged as a potential competitor to the silicon photovoltaic technology. The most representative perovskite cells employ SnO₂ and spiro-OMeTAD as the charge-transport materials. Despite their high efficiencies, perovskite cells with such a configuration show unsatisfactory lifespan, normally attributed to the instability of perovskites and spiro-OMeTAD. Limited attention was paid to the influence of SnO₂, an inorganic material, on device stability. Here we show that improving SnO₂ with a redox interfacial modifier, cobalt hexammine sulfamate, simultaneously enhances the power-conversion efficiency (PCE) and stability of the perovskite solar cells. Redox reactions between the bivalent cobalt complexes and oxygen lead to the formation of a graded distribution of trivalent and bivalent cobalt complexes across the surface and bulk regions of the SnO₂. The trivalent cobalt complex at the top surface of SnO₂ raises the concentration of (SO₃NH₂)⁻ which passivates uncoordinated Pb²⁺ and relieves tensile stress, facilitating the formation of perovskite with improved crystallinity. Our approach enables perovskite cells with PCEs of up to 24.91 %. The devices retained 93.8 % of their initial PCEs after 1000 hours of continuous operation under maximum power point tracking. These findings showcase the potential of cobalt complexes as redox interfacial modifiers for high-performance perovskite photovoltaics.

Nature Energy, Published online: 16 September 2024; doi:10.1038/s41560-024-01642-3

Publication date: January 2025

Source: Journal of Energy Chemistry, Volume 100

Author(s): Ranran Liu, Xin Zheng, Zaiwei Wang, Miaomiao Zeng, Chunxiang Lan, Shaomin Yang, Shangzhi Li, Awen Wang, Min Li, Jing Guo, Xuefei Weng, Yaoguang Rong, Xiong Li

Publication date: 1 December 2024

Source: Nano Energy, Volume 131, Part A

Author(s): Wenhui Lin, Jinxiong Wan, Jihuai Wu, Huiyuan Cui, Qing Yao, Puzhao Yang, Xiaoyuan Jiang, Dongbin Jiang, Ying Wang, Weihai Sun, Miaoliang Huang, Zhang Lan

A vacuum-assisted method, termed “prevacuum,” is introduced to improve the stability of nonfullerene organic solar cells. By subjecting the D18:Y6 active layer, deposited on indium tin oxide/hole transport layer (ITO/HTL) to a low-pressure vacuum before thermal annealing, stability improves by removing volatile components and impurities, resulting in a stable active layer, extending the time for 30% power loss.

Herein, a straightforward vacuum-assisted method is introduced to enhance the stability of nonfullerene organic solar cells (OSCs). The method, termed “prevacuum” involves subjecting the active layer (D18:Y6) to a low-pressure vacuum (−1 bar) before thermal annealing at 100 °C. Compared to untreated devices, prevacuum-treated OSCs exhibit a notable increase in power conversion efficiency from 13.71% to 14.90%. This enhancement is attributed to improved light absorption and charge extraction, as evidenced by external quantum efficiency measurements. Moreover, prevacuum treatment significantly improves device stability under operational conditions, with a 30% power loss occurring after 8.25 h compared to 4.5 h for untreated devices. This improvement is attributed to the removal of volatile components and impurities during the vacuum process, leading to a more hydrophobic and stable active layer. The study demonstrates the efficacy of prevacuum treatment as a simple and accessible method for enhancing the performance and longevity of OSCs, paving the way for their broader application in sustainable energy technologies.

Optical simulations done on monolithic perovskite/silicon tandem solar cells predict that decreasing the TCO thicknesses both at the front side and at recombination junction increases the photocurrent. 20.3 mA/cm² short circuit current density is obtained by ITO thicknesses of 25 nm and 20 nm at the front and recombination sides, respectively.

Optical losses of perovskite/silicon tandem solar cells can be effectively reduced by optimizing the thin-film layer thicknesses. Herein, the thicknesses of DC sputtered indium tin oxide (ITO) films, which serve as the front electrode and the recombination layer connecting the subcells, are optimized to reach high transparency and good lateral charge transport simultaneously. Optical simulations of the full perovskite/silicon tandem solar cell stacks are performed to find the optimum recombination and front electrode ITO thicknesses for solar cells as well as modules. Implementation of the optimized 25 nm front electrode ITO thickness in semitransparent single-junction perovskite solar cells increases the short-circuit density by 1.5 mA cm⁻² compared to the former reference thickness of 75 nm. Combined with an optimized 20 nm recombination ITO layer, high short-circuit density of 20.3 mA cm⁻² is reached in perovskite/silicon tandem solar cell devices, which is the highest reported value for planar front perovskite/silicon tandem solar cells to the best of knowledge. Further interface passivation enables 28.8% power conversion efficiency.

Adding glycine hydrochloride to the precursor solution enhances the photovoltaic performance and stability of solution-processed narrow-bandgap mixed Pb–Sn perovskites. The higher stability and device performance are related to the ability of glycine hydrochloride to retard the oxidation of Sn²⁺, improve crystallization and grain size distribution, reduce non-radiative recombination, and slow the recombination of charge carriers.

Additives are commonly used to increase the performance of metal-halide perovskite solar cells, but detailed information on the origin of the beneficial outcome is often lacking. Herein, the effect of glycine hydrochloride is investigated when used as an additive during solution processing of narrow-bandgap mixed Pb–Sn perovskites. By combining the characterization of the photovoltaic performance and stability under illumination, with determining the quasi-Fermi level splitting, time-resolved microwave conductivity (TRMC), and morphological and elemental analysis a comprehensive insight is obtained. Glycine hydrochloride is able to retard the oxidation of Sn²⁺ in the precursor solution, and at low concentrations (1–2 mol%) it improves the grain size distribution and crystallization of the perovskite, causing a smoother and more compact layer, reducing non-radiative recombination, and enhancing the lifetime of photogenerated charges. These improve the photovoltaic performance and have a positive effect on stability. By determining the quasi-Fermi level splitting on perovskite layers without and with charge transport layers it is found that glycine hydrochloride primarily improves the bulk of the perovskite layer and does not contribute significantly to passivation of the interfaces of the perovskite with either the hole or electron transport layer (ETL).

This work presents an effective way to construct high-performance and stable orgain solar cells (OSCs) by modifying active layer morphology and vertical phase distribution in all-polymer systems. Through the synergistic effect of LBL structure and dual donor strategy, a power conversion efficiency (PCE) of 18.18% is achieved. Further, thanks to the sequential deposition method, PBQx-T-Cl:PTzBI-dF/PY-IT achieves a higher PCE of 18.83% after the fine optimization.

Abstract

All-polymer systems are promising for commercial applications because the lower diffusivity of polymers helps to inhibit the large-scaled phase separation and obtain excellent stability. Achieving a fine-tuned morphology of the active layer with an appropriate vertical phase has long been a major goal in obtaining efficient all-polymer solar cells (all-PSCs). Herein, through the synergistic effect of layer-by-layer (LBL) structure and dual donor strategy, high performance and stable all-PSCs are prepared by constructing an interpenetrating network. The introduction of the third component PTzBI-dF suppresses excessive aggregation and reduces exciton recombination. The formation of a favorable p-i-n structure helps to adjust the vertical phase distribution and improve stability. Ultimately, through the fine optimization, PBQx-T-Cl:PTzBI-dF/PY-IT achieves a high PCE of 18.83%. This research demonstrates a simple and effective way to construct high-performance OSCs by desirable active layer morphology and vertical phase distribution.

The commercialization of PVSCs is hindered by poor reproducibility due to the chemical instability of the solution-processed materials. We first observe that the aging phenomenon is more pronounced in the precursor solution of the two-step sequential method compared to that in the one-step method due to the difference in the used solvents. Here, an effective targeted strategy for precursor stabilization by introducing benzene-1,3-dithiol (BDT) and decamethylferrocene (FcMe₁₀) additives into the organic amine salt solution and the PbI₂ precursor solution, thus extending the shelf-life of the two-step precursor solutions.

Abstract

Precursor solution aging process can cause significant influence on the photovoltaic performance of perovskite solar cells (PVSCs). Notably, we first observe that the aging phenomenon is more severe in the precursor of two-step sequential method compared to that in one-step method due to that the protic solvent isopropanol facilitates amine-cation side reaction and iodide ions oxidation. Herein, we report a novel approach for selectively stabilizing both organic amine salt and lead iodide (PbI₂) precursor solutions in two-step method. The introduction of benzene-1,3-dithiol into organic amine salt solution can mitigate amine-cation side reactions due to the formation of an acidic and reducing environment. Simultaneously, decamethylferrocene (FcMe₁₀/FcMe⁺ ₁₀) pair can act as a redox shuttle in PbI₂ solution to concurrently oxidize Pb⁰ and reduce I₂ in cyclic manner. Consequently, the PVSCs device fabricated from ameliorative precursor solutions demonstrates superior power conversion efficiency of 25.31 %, retaining 95 % of its efficiency after 21 days of solution aging. Moreover, the unencapsulated devices maintain 85 % of primitive efficiency for 1500 h at maximum power point tracking under continuous illumination. This work establishes a fundamental guidance and scientific direction for the stabilization of two-step perovskite precursor solutions.

In this study, a stable and environmental benign Sb₂(S _x Se_1−x )₃ thin-film photovoltaic (PV) cell is reported. After adjusting the Se/S atomic ratio, the pure sulfide Sb₂S₃ device with a large bandgap of 1.74 eV achieves an efficiency of over 20% under 1000 lux illumination, indicating great potential of this type of material in indoor photovoltaics (IPVs).

Antimony selenosulfide Sb₂(S _x Se_1−x )₃ is featured as a stable, environment-friendly, and low-cost light-harvesting material with a tunable bandgap in the range of 1.1–1.8 eV, satisfying the requirement of indoor photovoltaics (IPVs). Up to now, the certified efficiency of Sb₂(S _x Se_1−x )₃ solar cell with 1.45 eV bandgap has broken 10% under standard illumination (AM1.5G). However, this bandgap is not suitable for IPVs in terms of spectral matching. Herein, for the first time, the effect of optical bandgap of Sb₂(S _x Se_1−x )₃ on photovoltaic performance of the devices under AM1.5G and indoor light conditions is studied systematically. It is discovered that although an appropriate Se/S atomic ratio is beneficial for improving the crystallinity of Sb₂(S _x Se_1−x )₃ film and passivating the trap states, the band gap remains a key factor in determining the suitability of this material for IPVs. As a result, solar cells based on Sb₂S₃ with a large bandgap of 1.74 eV achieve an optimal efficiency of 20.34% under 1000 lux indoor illumination. Moreover, a high IPV efficiency of over 16% can still be maintained within a wide bandgap range from 1.5 to 1.7 eV, demonstrating the great potential of Sb-based chalcogenide as a light-harvesting material for IPVs.

A composite electron transport layer (ETL) ZnO/ZrSe₂ is constructed, which reduces the work function of ZnO under the effect of interface dipole moment and electron migration and makes the energy level between ETL and active layer more matching, the power conversion efficiency of OSCs with PM6:L8-BO as the active layer is improved from 17.34% to 18.24%.

Abstract

As an electron transport layer (ETL) widely used in organic solar cells (OSCs), ZnO has problems with energy level mismatch with the active layer and excessive defects on the ZnO surface, which can reduce the efficiency of OSCs. Here, ZnO/ZrSe₂ composite is fabricated by modifying ZnO with 2D ZrSe₂. The XPS and first-principles calculation (FPC) show that ZnO obtains electrons from ZrSe₂ and forms interfacial dipoles toward the active layer, which decreases the work function of ZnO, thus reducing the interface barrier and favoring the collection of electrons in OSCs. At the same time, after ZrSe₂ modification, the oxygen vacancy density on the ZnO surface decreases, thus improving the conductivity of ZnO. More importantly, the femtosecond transient absorption (Fs-TA) shows that ZrSe₂ selectively traps holes from the active layer, which prevents the holes from entering the ZnO, thereby reducing the probability of electron recombination. Finally, ZnO/ZrSe₂ composite is used as a novel ETL in OSCs with PBDB-T: ITIC, PM6:Y6 and PM6: L8-BO as active layers, and obtaining 12.09%, 16.34%, and 18.24% efficiency, respectively. This study provides a method for the interface modification of ZnO, and further investigates the role of 2D nanosheets in the interface modification.

Perovskite/silicon tandem solar cells have attracted significant attention for their potential to surpass the single-junction Shockley–Queisser limit. This review highlights the milestones and advancements in monolithic perovskite/silicon tandem solar cells over the past decade. It covers research progress and challenges, and provides a roadmap for developing efficient, scalable, and stable tandem solar cells.

Abstract

The perovskite/silicon tandem solar cell represents one of the most promising avenues for exceeding the Shockley–Queisser limit for single-junction solar cells at a reasonable cost. Remarkably, its efficiency has rapidly increased from 13.7% in 2015 to 34.6% in 2024. Despite the significant research efforts dedicated to this topic, the “secret” to achieving high-performance perovskite/silicon tandem solar cells seems to be confined to a few research groups. Additionally, the discrepancies in preparation and characterization between single-junction and tandem solar cells continue to impede the transition from efficient single-junction to efficient tandem solar cells. This review first revisits the key milestones in the development of monolithic perovskite/silicon tandem solar cells over the past decade. Then, a comprehensive analysis of the background, advancements, and challenges in perovskite/silicon tandem solar cells is provided, following the sequence of the tandem fabrication process. The progress and limitations of the prevalent stability measurements for tandem devices are also discussed. Finally, a roadmap for designing efficient, scalable, and stable perovskite/silicon tandem solar cells is outlined. This review takes the growth history into consideration while charting the future course of perovskite/silicon tandem research.

Two difluorobenzothiadizole (ffBT)-based copolymers, PffBT-2T and PffBT-4T, were synthesized to assess their impact on device performance. PffBT-4T demonstrated lower miscibility with L8-BO, leading to improved phase separation and enhanced molecular packing in the active layer. This optimized morphology, along with a prolonged nucleation and crystal growth process, resulted in a record efficiency of 17.5 % for ffBT-based photovoltaic polymers.

Abstract

The difluorobenzothiadizole (ffBT) unit is one of the most classic electron-accepting building blocks used to construct D-A copolymers for applications in organic solar cells (OSCs). Historically, ffBT-based polymers have achieved record power conversion efficiencies (PCEs) in fullerene-based OSCs owing to their strong temperature-dependent aggregation (TDA) characteristics. However, their excessive miscibility and rapid aggregation kinetics during film formation have hindered their performance with state-of-the-art non-fullerene acceptors (NFAs). Herein, we synthesized two ffBT-based copolymers, PffBT-2T and PffBT-4T, incorporating different π-bridges to modulate intermolecular interactions and aggregation tendencies. Experimental and theoretical studies revealed that PffBT-4T exhibits reduced electrostatic potential differences and miscibility with L8-BO compared to PffBT-2T. This facilitates improved phase separation in the active layer, leading to enhanced molecular packing and optimized morphology. Moreover, PffBT-4T demonstrated a prolonged nucleation and crystal growth process, leading to enhanced molecular packing and optimized morphology. Consequently, PffBT-4T-based devices achieved a remarkable PCE of 17.5 %, setting a new record for ffBT-based photovoltaic polymers. Our findings underscore the importance of conjugate backbone modulation in controlling aggregation behavior and film formation kinetics, providing valuable insights for the design of high-performance polymer donors in organic photovoltaics.

Publication date: 1 December 2024

Source: Nano Energy, Volume 131, Part A

Author(s): Yajun Cao, Yinghui Wu, Guoxu Liu, Xuyang Zhang, Xingyi Dai, Jiaxin Han, Junfeng Wang, Junle Qu, He Ni, Chi Zhang, Long-Biao Huang

Publication date: 1 December 2024

Source: Nano Energy, Volume 131, Part A

Author(s): Guocong Chen, Gangsen Su, Xusheng Zhang, Qiang Sun, Han Gao, Kaiyuan Liu, Hao Li, Jiafeng Wang, Dong He, Guoqiang Ma, Zeyu Niu, Tianle Cheng, Zhaoning Li, Peter Raymond Slater, Zhubing He

Herein, material cost, equipment depreciation cost, and energy consumption of different types of perovskite solar cells are analyzed in detail. The results show that when the conductive substrate and perovskite layer are identical, the use of carbon electrodes instead of metal electrodes and hole transport layers significantly reduces manufacturing costs ($41.16 for a 1 m² device), which is an obvious advantage.

Perovskite solar cells (PSCs) have attracted widespread attention due to their low cost and high efficiency. So far, a variety of single-junction PSCs have been successfully developed and considered for commercialization, including normal PSCs (N-PSCs), inverted PSCs (I-PSCs), and carbon-based PSCs (C-PSCs) without hole transporter. Herein, the material cost, equipment depreciation cost, and energy consumption of these three types of PSCs (1 m²) in detail are analyzed. As indicated, the total fabrication cost of the N-PSCs ($86.49) and I-PSCs ($81.31) is very close, but is significantly reduced to $41.16 for the C-PSCs (49%–52% reduction) because carbon electrode is much cheaper than noble metal electrode and organic hole transporter. Besides, only a low-cost slot-die coating process with low energy consumption is needed for the deposition of carbon electrode, while the expensive physical vapor deposition and reactive plasma deposition processes with high energy consumption are needed for the deposition of the noble metal electrode and organic hole transporter.

The Three symmetrical donor–acceptor interfacial dipole molecules are designed and synthesized with identical hole transport backbone and different anchoring groups, which regulate the surface work function and energy-level alignment of perovskites, improve charge extraction, and reduce energy loss at the interface. PzTN-modified PSC achieved a champion power conversion efficiency of 25.34% with a photovoltage of 1.176 V and a fill factor (FF) of 83.27%, accompanied by almost undetectable hysteresis and excellent operating stability.

Abstract

Interface engineering has become the mainstream for improving the performance of perovskite solar cells (PSCs). Interfacial dipole (ID) molecules have emerged as a feasible and effective strategy to alleviate the charge carrier loss and energy loss in PSCs. Here, the three symmetrical donor–acceptor interfacial dipole molecules (named PzT, PzTE, and PzTN) are designed and synthesized with identical hole transport backbone and different anchoring groups. The ID molecule is introduced into the interface between the perovskite layer and the hole transport layer. The dipole moments of ID molecules regulate the surface work function and energy-level alignment of perovskites, improve charge extraction, and reduce energy loss at the interface. Meanwhile, the anchoring groups of ID molecules coordinate with the defects on the surface of PVK and HTL, reduce interfacial trap state density and charge accumulation, and mitigate the carrier non-radiative recombination losses. As a result, PzTN-modified PSC achieved a champion power conversion efficiency of 25.34% with a photovoltage of 1.176 V and a fill factor (FF) of 83.27%, accompanied by almost undetectable hysteresis and excellent operating stability. This research demonstrates a feasible strategy for efficient and stable PSCs by interfacial dipole molecules.

Lead-halide perovskites commonly exhibit power-law decay rather than exponential decay at long delay times. As a result, obtaining quantitative information about the material properties becomes challenging. Additionally, determining a constant lifetime is no longer a feasible approach. In this article, the underlying factors are examined and solutions are proposed.

Abstract

Transient photoluminescence is a frequently used method in the field of halide perovskite photovoltaics to quantify recombination by determining the characteristic decay time of an exponential decay. This decay time is often considered to be a single value for a certain perovskite film. However, there are many mechanisms that lead to non-exponential decays. Here, it is shown that photoluminescence decays in many lead-halide perovskites are non-exponential and follow a power-law relation between PL intensity and time that is caused by shallow defects. Decay times therefore vary continuously as a function of time and injection level. In situations where recombination is bimolecular and decays follow a power law, the differential decay time equals the time delay after the laser pulse for long time delays and therefore completely lacks quantitative information about the recombination rate. Quantifying recombination using transient PL measurements, therefore, requires analyzing the lifetime as a function of injection level rather than time. As an alternative to the continuously varying decay time, a bimolecular recombination coefficient can also be determined, which correlates with the photoluminescence quantum efficiency. Finally, the influence of the repetition rate and the background subtraction method on the analysis of power-law type PL decays is discussed.