Chen Weijie

It is found that the TFFH additive can inhibit the oxidation of I⁻, eliminating I⁰, Pb⁰, and uncoordinated Pb²⁺ defects and control crystallization kinetics by the strong FA⁺···TFFH···Pb─I interaction. Simultaneous regulation of precursor solution and crystallization dynamics mean the optimized solar cells achieve improved reproducibility and stability, and reach an efficiency of 42.43% at illumination of 1002 lux.

Abstract

The efficiency of metal halide perovskite solar cells (PSCs) has skyrocketed; however, defects created by aging precursor solutions and during crystallization pose a significant barrier to the reproducibility and efficiency of solar cells. In this work, fluoro-N,N,N″,N″-tetramethylformamidinium hexafluorophosphate (F-(CH₃)₄CN₂PF₆, abbreviated as TFFH) is introduced to stabilize precursor solution and improve crystallization dynamics simultaneously for high-performance formamidinium lead iodide (FAPbI₃)-based perovskite indoor photovoltaics. The TFFH stabilizes the precursor solution by inhibiting oxidation of I⁻ and reducing newly generated I⁰ to I⁻, and passivates undercoordinated Pb²⁺ by interacting with the Pb─I framework. Time-resolved optical diagnostics show prolonged perovskite crystallization dynamics and in situ defect passivation due to the presence of strong FA⁺···TFFH···Pb─I interaction. Simultaneous regulation of precursor solution and crystallization dynamics guarantee larger perovskite grain sizes, better crystal orientation, fewer defects and more efficient charge extraction in PSCs. The optimized PSCs achieve improved reproducibility and better stability and reach an efficiency of 42.43% at illumination of 1002 lux, which is the highest efficiency among all indoor photovoltaics. It is anticipated that the concurrent stabilization of solutions and regulation of crystallization dynamics will emerge as a prevalent approach for enhancing the reproducibility and efficiency of perovskite.

An efficient fully solution-processed interconnecting layer (ICL) of PEDOT:F/ZnO has been developed for both two-junction and triple-junction tandem organic solar cells with good performance and stability. The ICL is further used to fabricate large-area tandem organic module (15.48 cm²) that shows an open-circuit voltage of 10.25 V, fill factor of 75.1%, and a power conversion efficiency of 13.24%.

Interconnecting layer (ICL) is a key part of the tandem organic solar cells (OSCs) to achieve high efficiency. The ICLs of efficient inverted nonfullerene OSCs are complicated that comprise vacuum-deposited MoO₃, solution-processed ZnO, and an additional thin silver (or PEDOT:PSS) film in between. Herein, an efficient fully solution-processed ICL is first reported that comprises a PEDOT:F layer and a ZnO layer. The PEDOT:F is short for poly(3,4-ethylenedioxythiophene):perfluorinated sulfonic acid ionomer that is alcohol dispersed and has a work function of 5.6 eV for hole collection. The ZnO is used for electron collection. The PEDOT:F/ZnO has a conductivity of 2.28 × 10⁻³ S cm⁻¹ which can play a recombination zone. The solution-processed ICL of PEDOT:F/ZnO has been validated in both two-junction and triple-junction solar cells. The tandem cells show high fill factor (FF) of 76–80% and high open-circuit voltage (V _OC) which is nearly the sum of the single-junction OSCs. The PEDOT:F/ZnO ICL has also been used to fabricate large-area tandem organic module (15.48 cm²) that shows a V _OC of 10.25 V, FF of 75.1%, and a power conversion efficiency of 13.24%. The PEDOT:F/ZnO is a promising ICL for high-performance tandem OSCs.

A simple and effective way to obtain an ideal pseudo p–i–n structure via optimizing donor morphology and constructing favorable vertical component distribution in all-polymer solar cell is demonstrated. Through solvent engineering, a higher power conversion efficiency (17.53%) has been achieved in layer-by-layer devices with donor D18 processed by o-xylene and carbon disulfide, higher than chloroform (16.49%) and chlorobenzene (16.04%).

All-polymer solar cells (all-PSCs) have attracted extensive attention for their advantages in long-term thermal- and photostability. However, the power conversion efficiencies (PCEs) of all-PSCs still lag behind organic solar cells based on small-molecular acceptors. The long-chain entanglement between polymers brings complex morphological problems, which contribute to lower fill factor (FF). Herein, an effective approach is proposed to build the ideal morphology and pseudo-p–i–n vertical component distribution in all-polymer active layer by independently casting donor and acceptor films with different solvents. Through the solvent engineering, the layer-by-layer device with o-xylene and carbon disulfide (O-XY:CS₂)-processed D18 donor layer achieves a PCE of 17.53%, much higher than commonly used solvents (chloroform and chlorobenzene) processed donor layers with PCEs of 16.49 and 16.04%, respectively. In-depth investigation reveals that outstanding performance of O-XY:CS₂-processed donor layer device is attributed to mitigated bimolecular recombination, more balanced mobility, and reduced trap density of states, which contribute to the enhancement of short-current density and FF. Moreover, favorable morphology network also brings prolonged lifetime under continuous light soaking. This work presents a simple and effective way to obtain ideal active layer morphology and construct favorable vertical component distribution through optimizing donor morphology in all-PSCs.

Obtaining a uniform perovskite layer on Me-4PACz self-assembled monolayer (SAM) presents significant challenges. This is because of poor perovskite ink interaction with the Me-4PACz SAM. Herein, a perovskite ink–substrate interaction strategy is employed using a triple co-solvent system. As a result, a uniform perovskite layer is obtained with improved and reproducible device performance.

Abstract

Perovskite solar cells employing [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) self-assembled monolayer as the hole transport layer have been reported to demonstrate a high device efficiency. However, the poor perovskite wetting on Me-4PACz caused by poor perovskite ink interaction with the underlying Me-4PACz presents significant challenges for fabricating efficient perovskite devices. A triple co-solvent system comprising dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidone (NMP) is employed to improve the perovskite ink - Me-4PACz coated substrate interaction and obtain a uniform perovskite layer. In comparison to DMF- and DMSO-based inks, the inclusion of NMP shows considerably higher binding energies of the perovskite ink with Me-4PACz as revealed by density-functional theory calculations. With the optimized triple co-solvent ratio, the perovskite devices deliver high power conversion efficiencies of >20%, 19.5%, and ≈18.5% for active areas of 0.16, 0.72, and 1.08 cm², respectively. Importantly, this perovskite ink–substrate interaction approach is universal and helps in obtaining a uniform layer and high photovoltaic device performance for other perovskite compositions such as MAPbI₃, FA_{1− x} MA _x PbI_{3– y} Br _y , and MA-free FA_{1− x} Cs _x PbI_{3– y} Br _y .

The unfavorable conductivity of existing transparent conducting oxide electrodes restricts the development of large-area perovskite solar cells. Herein, buried-metal-grid tin-doped indium oxide electrodes are developed based on a photolithography technique. Such electrodes with greatly enhanced conductivity and low-height metal steps help increase device performance and mitigate performance loss while upscaling cell area.

Abstract

The limited conductivity of existing transparent conducting oxide (TCO) greatly restricts the further performance improvement of perovskite solar cells (PSCs), especially for large-area devices. Herein, buried-metal-grid tin-doped indium oxide (BMG ITO) electrodes are developed to minimize the power loss caused by the undesirable high sheet resistance of TCOs. By burying 140-nm-thick metal grids into ITO using a photolithography technique, the sheet resistance of ITO is reduced from 15.0 to 2.7 Ω sq⁻¹. The metal step of BMG over ITO has a huge impact on the charge carrier transport in PSCs. The PSCs using BMG ITO with a low metal step deliver power conversion efficiencies (PCEs) significantly better than that of their counterparts with higher metal steps. Moreover, compared with the pristine ITO-based PSCs, the BMG ITO-based PSCs show a smaller PCE decrease when scaling up the active area of devices. The parallel-connected large-area PSCs with an active area of 102.8 mm² reach a PCE of 22.5%. The BMG ITO electrodes are also compatible with the fabrication of inverted-structure PSCs and organic solar cells. The work demonstrates the great efficacy of improving the conductivity of TCO by BMG and opens up a promising avenue for constructing highly efficient large-area PSCs.

Nature Communications, Published online: 05 September 2023; doi:10.1038/s41467-023-41149-1

Further extending the band edge of perovskite approaching the ideal bandgap of single-junction solar cell is essential to improve device efficiency. Here, the authors integrate optical resonances with perovskite solar cells to extend the band edge, achieving EQE-integrated current of 26.0 mA/cm2.

PbI₂-excess perovskite solar cells generally show low stability. In this work, anion exchange of Br⁻ in perovskite and I⁻ in excess PbI₂ at grain boundary and interface of the perovskite layers induced by high temperature is found to be an important mechanism which affects the device stability.

The photodecomposition of PbI₂ in the perovskite halide structure has been identified as a primary reason for the rapid degradation of metal halide perovskite solar cells (PSCs) under continuous illumination. In particular, excess PbI₂ on the surface of perovskite films reduces the stability of PSCs via several mechanisms that are still unelucidated. Herein, the influence of excess PbI₂ on PSCs is investigated by varying the Au deposition rate, which results in different temperatures during the fabrication of PSCs, and then they are compared with stoichiometric PSCs. It is demonstrated that the anion exchange of Br⁻ in perovskite and I⁻ in excess PbI₂ occurs at the grain boundary and interface of the perovskite layers induced by the high heating temperature, leading to a photoluminescence peak redshift and lower power conversion efficiency. Light illumination accelerates the exchange of Br⁻ and I⁻ between the perovskite layer and excess PbI₂ induced by carrier accumulation at the interface and grain boundary, leading to the poor stability of the PSCs.

Ternary-metal Sn-Pb-Zn perovskite exhibits reconstructed surface to balance the Sn/Pb distribution, tuning the interface energy and inducing strong ionic bonding by the surface-rich Zn. The novel alloy method promotes the interface charge transfer, achieving efficient and stable solar cells.

Abstract

Though Sn-Pb alloyed perovskite solar cells (PSCs) achieved great progress, there is a dilemma to further increase Sn for less-Pb requirement. High Sn ratio (>70%) perovskite exhibits nonstoichiometric Sn:Pb:I at film surface to aggravate Sn²⁺ oxidation and interface energy mismatch. Here, ternary metal alloyed (FASnI₃)_0.7(MAPb_{1− x} Zn _x I₃)_0.3 (x = 0–3%) is constructed for Pb% < 30% perovskite. Zn with smaller ionic size and stronger ionic interaction than Sn/Pb assists forming high-quality perovskite film with ZnI₆ ⁴⁻ enriched at surface to balance Sn:Pb:I ratio. Differing from uniform bulk doping, surface-rich Zn with lower lying orbits pushes down the energy band of perovskite and adjusts the interface energy for efficient charge transfer. The alloyed PSC realizes efficiency of 19.4% at AM1.5 (one of the highest values reported for Pb% < 30% PSCs). Moreover, stronger bonding of Zn─I and Sn─I contributes to better durability of ternary perovskite than binary perovskite. This work highlights a novel alloy method for efficient and stable less-Pb PSCs.

Ternary copolymerization strategy and side-chain engineering are employed to develop three dopant-free hole-transporting materials for perovskite solar cells. Terpolymer PT-Cz50 bearing the optimal side-chain ratio of thiophene and carbazole also surpass its polymer blend counterpart PA-Cz50, due to the superior molecular aggregation and stacking pattern, and endows the devices a champion power conversion efficiency of 22.53% and high stability.

Abstract

The binary electron donor–electron acceptor (D-A) type conjugated polymers have proven to be efficient dopant-free hole-transporting materials (HTMs) for the n-i-p perovskite solar cells (PVSCs). However, D-A type terpolymeric HTMs containing two D units are not exploited. Reserving the high-planarity backbone of benzodithiophene (BDT)-benzodithiophene-4,8-dione, D₁-A-D₂-A type terpolymers PT-Cz30, PT-Cz50, and PT-Cz70 are obtained by side-chain engineering and ternary copolymerization strategy, in which BDT bearing the side chains of thiophene and carbazole serves as D₁ and D₂ units, respectively. PT-Cz50 performs best due to the appropriate side-chain ratio around 1:1. Meanwhile, a polymer blend HTM PA-Cz50 is studied for comparison, in which two binary D-A polymers PBDB-T and PBDB-Cz are blended with the molar ratio of 1:1. Containing similar side-chain composition, terpolymer PT-Cz50 presents superior hole transport properties over the polymer blend PA-Cz50 and endows better device performances to the PVSCs with a promising power conversion efficiency of 22.53% and high device stability.

Wide-bandgap perovskites are relevant materials for tandem cells. However, the addition of bromine, to increase the bandgap, leads to the formation of a perovskite richer in defects, with halide distribution heterogeneity and photoinstability. Here, the study of the impact and mode of action of methylammonium chloride (MACl) additive, shows the inhibition of intermediates formation and the halide distribution homogenization with MACl.

Abstract

Wide-bandgap perovskites are of paramount importance as the photoactive layer of the top cell in high-efficiency tandem solar cells. Comparably high Br contents are required to widen the perovskite bandgap. However, the increase in Br content causes heterogeneous halide distribution and photoinstability. Here, the positive effect of the additive methylammonium chloride (MACl) on the optical and electronic properties of Br-rich perovskite, deposited using N-methyl-2-pyrrolidone (NMP) as co-solvent and the gas quenching method, is investigated. Simultaneous in situ grazing-incidence wide-angle X-ray scattering and photoluminescence spectroscopy are used to track the evolution of the structural and optoelectronic properties of the perovskites with different amounts of Br and MACl during the spin-coating and thermal annealing steps. The formation mechanism is elucidated in the presence of MACl. It is observed that chloride ions inhibit the intermediate phases, favoring the formation of a perovskite phase with higher crystallinity. Nano X-ray fluorescence mapping recognizes Br-richer and poorer nanometric domains, whose average sizes reduce for samples with MACl. In conclusion, it is demonstrated that adding MACl affects the formation of wide-bandgap perovskites via destabilization of the intermediate phases and acts on the homogenization of the halide distribution, leading to improved solar cell performances.

Asymmetric alkyl chain engineering is employed to design a new acceptor named DTC11. When matched with D18 and processed by non-halogen solvent, the device achieves a power conversion efficiency (PCE) of 19.0%. Investigations reveal that enhanced exciton generation, diffusion, and dissociation as well as weak recombination exist in device. Furthermore, 21 cm² blade-coated large-area module realizes a PCE of 15.4%.

Abstract

The effective molecular design of non-fullerene acceptors is important to high-efficiency organic solar cells. Herein, asymmetric alkyl chain engineering is applied to design a new acceptor named DTC11. Compared with the model accpetor DTY6 with two long-branched alkyl chains (2-decyltetradecyl) on dithie-nothiophen[3.2-b]-pyrrolobenzothiadiazole central unit, DTC11 owns a 2-decyltetradecyl chain and an undecyl chain in the inner bay side of the central unit. It is found that with such modification of asymmetric long alkyl side chains, the crystallinity, absorption coefficient, and exciton lifetime of DTC11 are all improved. Moreover, in comparison with D18:DTY6 device, non-halogen solvent processed D18:DTC11 device shows enhanced exciton generation and dissociation, improved charge transport as well as weak recombination, promoting higher short-circuit current density and fill factor. Consequently, D18:DTC11 device delivers an outstanding efficiency of 19.0%. More significantly, non-halogen solvent processed D18:DTC11 large-area module (active area 21 cm²) is fabricated by blade coating, and an impressive efficiency of 15.4% with fill factor of 74.6% is realized. This study demonstrates that the asymmetric alkyl chain engineering is a feasible strategy to design non-fullerene acceptor with high-performance and non-halogen solvent processability, which are very essential for the commercialization of large-area module.

Here, 5-chloro-2-hydroxypyridine derivatives with –F (HFCLP) and –NH₂ (HNCLP) end groups are selected to realize the push-pull electronic structure configuration. The precise modulation of electron structure and the structure-activity relationship between electronic configuration and performance of the PSCs are explored.

Abstract

Targeted passivation of defects in perovskite is the primary consideration in the design of additives containing functional groups. However, the precise modulation of electron structure in functional groups and the structure-activity relationship between electronic configuration and performance of perovskite solar cells (PSCs) still need to be explored. In this study, 5-chloro-2-hydroxypyridine derivatives with –NH₂ (HNCLP) and –F (HFCLP) end groups are selected to realize the push-pull electronic structure configuration. Density functional theory demonstrates that, compared with HFCLP, HNCLP with the electron-donating terminal of –NH₂ has a long dipole moment and immobilize the interstitial I₃ ⁻, and the N side of pyridine with high-density electron cloud enables strong passivation with undercoordinated Pb²⁺ ions. The experimental results confirm that HNCLP with optimized electronic configuration emerges strong passivation ability, greatly suppresses the nonradiative recombination of perovskite absorber, and remarkably improves the film crystal quality along with the extraction and transfer process of photogenerated carriers. The HNCLP-contained PSC exhibits a remarkable efficiency of 24.47%, and HNCLP helps to enhance the moisture-proof of perovskite film and device storage stability.

Publication date: December 2023

Source: Journal of Energy Chemistry, Volume 87

Author(s): Yingyue Zhang, Wentao Zou, Youdi Zhang, Pei Cheng, Long Ye, Ke Gao

Perovskite solar cells integrated with an ambipolar polymer offer several advantages, such as comprehensive defect passivation, bidirectional charge transport, and suppression of lithium-ion migration. These attributes contribute to an enhancement in both performance and stability.

Abstract

Effective passivation of grain boundaries in perovskite solar cells is essential for achieving high device performance and stability. However, traditional polymer-based passivation strategies can introduce challenges, including increased series resistance, disruption of charge transport, and insufficient passivation coverage. In this study, a novel approach is proposed that integrates a multifunctional ambipolar polymer into perovskite solar cells to address these issues. The ambipolar polymer is successfully incorporated into both the perovskite film and the hole transport layer (HTL), enabling comprehensive restoration of defect sites within the perovskite active layer. Moreover, this approach yields additional advantages for perovskite devices, such as enabling bidirectional charge transport, limiting pinhole formation at the HTL, reducing lithium-ion migration from the HTL to the perovskite, and minimizing both the band offset and surface energy difference between the perovskite film and HTL interface. With these benefits, the ambipolar polymer integrated device achieves a power conversion efficiency (PCE) of 24.0%. Remarkably, it also exhibits enhanced long-term stability, preserving 92% of its initial PCE after 2000 h under ambient conditions, and 80% of its initial PCE after 432 h under harsh conditions (at 85 °C and 85 ± 5% RH).

A small molecular uracil additive is developed to passivate the defects of the perovskite film and enhance the interface binding force between perovskite film and substrate. The device delivers a champion efficiency of 24.23%. The device exhibits superior operational stability maintaining over 90% of its initial efficiency after tracking for 6000 h at the maximum power point.

Abstract

The operational stability is a huge obstacle to further commercialization of perovskite solar cells. To address this critical issue, in this work, uracil is introduced as a “binder” into the perovskite film to simultaneously improve the power conversion efficiency (PCE) and operational stability. Uracil can efficiently passivate defects and strengthen grain boundaries to enhance the stability of perovskite films. Moreover, the uracil also strengthens the interface between the perovskite and the Tin oxide (SnO₂) electron transport layer to increase the binding force. The uracil-modified devices deliver a champion PCE of 24.23% (certificated 23.19%) with negligible hysteresis at active area of 0.0625 cm². In particular, the optimal device exhibits over 90% of its initial PCE after tracking for ≈6000 h at its maximum power point under continuous light, indicating its superior operational stability. Moreover, the devices also show great reproducibility in both PCE and operational stability.

Publication date: 20 September 2023

Source: Joule, Volume 7, Issue 9

Author(s): Tianpeng Li, Feifei He, Jia Liang, Yabing Qi

It is found that a hydrogen-sulfate-based ionic liquid additive enables the phase-conversion pathway of precursors → solvated intermediates → α-FAPbI₃, which results in the self-elimination of defects during crystallization. The improved perovskite crystallization dynamics finally endow solar cells with high efficiencies of 25.14% at 300 K and 26.12% at 240 K.

Abstract

Understanding and controlling crystallization is crucial for high-quality perovskite films and efficient solar cells. Herein, the issue of defects in formamidinium lead iodide (FAPbI₃) formation is addressed, focusing on the role of intermediates. A comprehensive picture of structural and carrier evolution during crystallization is demonstrated using in situ grazing-incidence wide-angle X-ray scattering, ultraviolet–visible spectroscopy and photoluminescence spectroscopy. Three crystallization stages are identified: precursors to the δ-FAPbI₃ intermediate, then to α-FAPbI₃, where defects spontaneously emerge. A hydrogen-sulfate-based ionic liquid additive is found to enable the phase-conversion pathway of precursors → solvated intermediates → α-FAPbI₃, during which the spontaneous generation of δ-FAPbI₃ can be effectively circumvented. This additive extends the initial growth kinetics and facilitates solvent–FA⁺ ion exchange, which results in the self-elimination of defects during crystallization. Therefore, the improved crystallization dynamics lead to larger grain sizes and fewer defects within thin films. Ultimately, the improved perovskite crystallization dynamics enable high-performance solar cells, achieving impressive efficiencies of 25.14% at 300 K and 26.12% at 240 K. This breakthrough might open up a new era of application for the emerging perovskite photovoltaic technology to low-temperature environments such as near-space and polar regions.

Highly crystallized Cl-doped SnO₂ NCs that can form very stable aqueous dispersion with shelf life up to one year are herein prepared without the need of any stabilizer. The fabricated FAPbI₃ perovskite solar cells with the electron transport layers made by such NCs achieve champion efficiency up to ≈25% for small cell (0.085 cm²) and ≈20% for mini-module (12.125 cm²).

Abstract

Tin dioxide (SnO₂) with high conductivity and low photocatalytic activity has been reported as one of the best candidates for highly efficient electron transport layer (ETL) in perovskite solar cell (PSC). The state-of-the-art SnO₂ layer is achieved by chemical bath deposition with tunable properties, while the commercial SnO₂ nanocrystals (NCs) with low tunability still face the necessity of further improvement. Here, a kind of highly crystallized Cl-doped SnO₂ NCs is reported that can form very stable aqueous dispersion with shelf life up to one year without any stabilizer, which can facilitate the fabrication of PSCs with satisfactory performance. Compared to the commercial SnO₂ NCs regardless of the extrinsic Cl-doping conditions, the intrinsic Cl-doped SnO₂ NCs effectively suppress the energy barrier and reduces the trap state density at the buried interface between perovskite and ETL. Consequently, stable PSCs based on such Cl-doped SnO₂ NCs achieve a champion efficiency up to ≈25% for small cell (0.085 cm²) and ≈20% for mini-module (12.125 cm²), indicating its potential as a promising candidate for ETL in high-performance perovskite photovoltaics.

Two nonfused ring acceptors IOEH-4F and IOEH-N2F are synthesized by a green synthetic route and incorporated into PM6:Y6 blend. Encouragingly, the IOEH-4F and IOEH-N2F-based ternary tPSCs exhibited more efficient charge transfer, exciton separation, and lower energy loss. And the IOEH-4F and IOEH-N2F-based ternary PSCs achieved an impressive PCE of 17.80% and 18.13%, respectively.

Abstract

Ternary polymer solar cells(PSCs) have been identified as an effective approach to improving power conversion efficiency (PCE) of binary PSCs. However, most of the third component, especially Y-series non-fullerene acceptors, is a fused ring acceptor which often requires a rather tedious synthesis and the use of hazardous organostannane reagents. In this work, two nonfused ring acceptors IOEH-4F and IOEH-N2F are synthesized by a green synthetic route and incorporated into PM6:Y6 blend. Encouragingly, the IOEH-4F and IOEH-N2F-based ternary PSCs exhibited more efficient charge transfer, exciton separation, and lower energy loss than PM6:Y6-based PSCs. And the IOEH-4F and IOEH-N2F-based ternary PSCs achieved an impressive PCE of 17.80% and 18.13%, respectively, which are higher than that of PM6:Y6 based PSCs (16.18%). Notably, these PCE values are also the highest PCEs for ternary PSCs including non-fused ring acceptors. Importantly, even when the IOEH-N2F:Y6 ratios increased from 0.05:1.2 to 0.50:1.2, the PCE of IOEH-N2F-based ternary PSCs (16.70%) are still higher than that of PM6:Y6 based PSCs, indicating the great potential for cost saving. It is believed that the findings will help the design of better nonfused ring acceptors and the optimization of corresponding ternary PSCs with cost-saving advantage.

In the realm of air-processed organic solar cells (AP-OSCs), optimal charge-carrier dynamics play a critical role. These dynamics profoundly impact key processes such as exciton-dissociation, carrier-mobilities, and recombinations. Efficient AP-OSCs demand a delicate balance of pivotal factors including polaron formation, highest occupied molecular orbital (HOMO)-offset, quadruple-moments, cascaded energy-levels, and charge trahsfer (CT)-states. Understanding and engineering these factors/dynamics are imperative to fabricate efficient AP-OSCs under ambient conditions.

Abstract

Over the past couple of decades, immense research has been carried out to understand the photo-physics of an organic solar cell (OSC) that is important to enhance its efficiency and stability. Since OSCs undergoes complex photophysical phenomenon, studying these factors has led to designing new materials and implementing new strategies to improve efficiency in OSCs. In this regard, the invention of the non-fullerene acceptorshas greatly revolutionized the understanding of the fundamental processes occurring in OSCs. However, such vital fundamental research from device physics perspectives is carried out on glovebox (GB) processed OSCs and there is a scarcity of research on air-processed (AP) OSCs. This review will focus on charge carrier dynamics such as exciton diffusion, exciton dissociation, charge-transfer states, significance of highest occupied molecular orbital-offsets, and hole-transfer efficiencies of GB-OSCs and compare them with the available data from the AP-OSCs. Finally, key requirements for the fabrication of efficient AP-OSCs will be presented from a charge-carrier dynamics perspective. The key aspects from the charge-carrier dynamics view to fabricate efficient OSCs either from GB or air are provided.

A star-shaped triphenylene-based organic semiconductor is synthesized, exhibiting homogeneous, pinhole-free film morphology and improved hole conduction. Furthermore, this organic semiconductor possesses a high cohesive energy density, resulting in a large elastic modulus and slow diffusion of external species, enabling the fabrication of thermostable perovskite solar cells with an average efficiency surpassing 23.4%.

Abstract

Achieving the desired thermomechanical properties for highly solution-processable organic semiconductors is challenging but crucial for heat tolerance of emerging optoelectronic devices. To this end, the successful synthesis of triphenylene–ethylenedioxythiophene-dimethoxytriphenylamine (TP–ETPA), a star-shaped organic semiconductor, is reported through a direct arylation reaction that involves ETPA, an electron donor, being grafted densely onto TP, which possesses six electron-equivalent functionalization sites. Remarkably, TP–ETPA exhibits significantly improved hole mobility compared to 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-OMeTAD) at a given hole density, owing to its lower energetic disorder, larger average centroid distance, and smaller reorganization energy. TP–ETPA, with a molecular weight of 2888 Da and lacking flexible chains, demonstrates extraordinary solubility in nonpolar solvents, enabling the formation of dense, pinhole-free films through solution codeposition with an air-doping promoter. By utilizing the p-doped TP–ETPA composite as the hole transport layer, perovskite solar cells with an average power conversion efficiency of 23.4% are successfully fabricated. Notably, these devices display significantly enhanced operational stability and thermal stability at 85 °C. Molecular dynamics simulations reveal that the TP–ETPA-based hole transport layer possesses a high cohesive energy density, resulting in a large elastic modulus and slow diffusion of external species.

CCS Chemistry, Ahead of Print.

Nature Chemistry, Published online: 31 August 2023; doi:10.1038/s41557-023-01311-0

Two-dimensional hybrid perovskites have gained substantial interest recently due to their controllable optoelectronic properties; however precise control over layer thickness has been synthetically challenging. Now a crystal growth method is shown to achieve high-quality single crystals of organic semiconductor-incorporated perovskites with control over their thickness and length through judicious solvent choice, affording precisely tuned optoelectronic properties.

Publication date: 18 October 2023

Source: Joule, Volume 7, Issue 10

Author(s): Cheng Zhu, Chenyue Wang, Pengxiang Zhang, Sai Ma, Yihua Chen, Ying Zhang, Ning Yang, Mengqi Xiao, Xiaohua Cheng, Ziyan Gao, Kaichuan Wen, Xiuxiu Niu, Tinglu Song, Zhenhuang Su, Huachao Zai, Nengxu Li, Zijian Huang, Yu Zhang, Hao Wang, Huanping Zhou