Chen Weijie

A pH neutral solution-processed conjugated polyelectrolyte PIDT-F:IMC is developed as hole transport layer for efficient and stable organic solar cells (OSCs). The incorporation of PIDT-F:IMC can not only reduce the depletion region width at the anode interface, so as to suppress the energy loss in the hole extraction process, but also significantly improve the operational stability of OSCs.

Abstract

The large depletion region width at the electrode interface may cause serious energy loss in charge collection of organic solar cells (OSCs), depressing the open-circuit voltage and power conversion efficiency (PCE). Herein, a pH neutral solution-processed conjugated polyelectrolyte PIDT-F:IMC as hole transport layer (HTL) to reduce the depletion region width in efficient OSCs is developed. By utilizing “mutual doping” strategy, the doping density of PIDT-F:IMC is increased by more than two orders of magnitude, which significantly reduces the depletion region width at the anode interface from 55 to 7.4 nm, playing an effective role in decreasing the energy loss in hole collection. It is also revealed that the optimal thickness of HTL should be consistent with the depletion region width for achieving the minimum energy loss. The OSC modified by PIDT-F:IMC shows a high PCE of 18.2%, along with an amazing fill factor of 0.79. Moreover, a PCE of 16.5% is achieved in the 1 cm² OSC by using a blade-coated PIDT-F:IMC HTL, indicating the good compatibility of PIDT-F:IMC with large-area processing technology. The PIDT-F:IMC-modified OCS exhibits a lifetime of 400 h under operational conditions, which is ten times longer than that of the PEDOT:PSS device.

This review summarizes the intrinsic and extrinsic degradation pathways of tin-containing perovskite solar cells (PSCs) and discusses mitigation strategies to enhance their durability. Prospectives on potential avenues for advancing tin-containing PSCs are also presented.

Abstract

Tin (Sn)-containing perovskite solar cells (PSCs) have gained significant attention in the field of perovskite optoelectronics due to lower toxicity than their lead-based counterparts and their potential for tandem applications. However, the lack of stability is a major concern that hampers their development. To achieve the long-term stability of Sn-containing PSCs, it is crucial to have a clear and comprehensive understanding of the degradation mechanisms of Sn-containing perovskites and develop mitigation strategies. This review provides a compendious overview of degradation pathways observed in Sn-containing perovskites, attributing to intrinsic factors related to the materials themselves and environmental factors such as light, heat, moisture, oxygen, and their combined effects. The impact of interface and electrode materials on the stability of Sn-containing PSCs is also discussed. Additionally, various strategies to mitigate the instability issue of Sn-containing PSCs are summarized. Lastly, the challenges and prospects for achieving durable Sn-containing PSCs are presented.

Taurine is employed as the buried interface bridge to fabricate hole transport layer free low-bandgap perovskite solar cells, leading to a high efficiency of 22.50% with an impressive V _OC of 0.911 V, enabling all-perovskite tandem solar cells with an efficiency of 26.03%.

Abstract

Low-bandgap (LBG, E _g ≈1.25 eV) tin-lead (Sn-Pb) perovskite solar cells (PSCs) play critical roles in constructing efficient all-perovskite tandem solar cells (TSCs) that can surpass the efficiency limit of single-junction solar cells. However, the traditional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer (HTL) in LBG PSCs usually restricts device efficiency and stability. Here, a strategy of employing 2-aminoethanesulfonic acid (i.e., taurine) as the interface bridge to fabricate efficient HTL-free LBG PSCs with improved optoelectronic properties of the perovskite absorbers at the buried contacts is reported. Taurine-modified ITO substrate has lower optical losses, better energy level alignment, and higher charge transfer capability than PEDOT:PSS HTL, leading to significantly improved open-circuit voltage (V _OC) and short-circuit current density of corresponding devices. The best-performing LBG PSC with a power conversion efficiency (PCE) of 22.50% and an impressive V _OC of 0.911 V is realized, enabling all-perovskite TSCs with an efficiency of 26.03%. The taurine-based HTL-free TSCs have highly increased stability, retaining more than 90% and 80% of their initial PCEs after constant operation under 1-sun illumination for 600 h and under 55 °C thermal stress for 950 h, respectively. This work provides a facile strategy for fabricating efficient and stable perovskite devices with a simplified HTL-free architecture.

Amphoteric organic salt, 4FPEAPSA, is applied as the buried interface bridged layer to induce large-grain perovskite film with uniform morphology. 4FPEAPSA treatment can facilitate the matchable energy level alignment at the perovskite buried interface, reducing defect recombination loss. Such a multi-functional bridged layer enables a high efficiency of 25.03% and preferable stability in the inverted perovskite solar cells (PerSCs).

Abstract

Synergistic morphology and defects management at the buried perovskite interface are challenging but crucial for the further improvement of inverted perovskite solar cells (PerSCs). Herein, an amphoteric organic salt, 2-(4-fluorophenyl)ethylammonium-4-methyl benzenesulfonate (4FPEAPSA), is designed to optimize the film morphology and energy level alignment at the perovskite buried interface. 4FPEAPSA treatment promotes the growth of a void-free, coarse-grained, and hydrophobic film by inducing the crystal orientation. Besides, the dual-functional 4FPEAPSA can chemically interact with the perovskite film, and passivate the defects of iodine and formamidine vacancies, tending to revert the fermi level of perovskite to its defect-free state. Meanwhile, the formation of a p-type doping buried interface can facilitate the interfacial charge extraction and transport of PerSCs for reduced carrier recombination loss. Consequently, 4FPEAPSA treatment improves the efficiency of the perovskite devices to 25.03% with better storage, heat, and humidity stability. This work contributes to strengthening the systematic understanding of the perovskite buried interface, providing a synergetic approach to realize precise morphology control, effective defect suppression, and energy level alignment for efficient PerSCs.

This work developed benzothieno[3,2-b]thiophene-based noncovalently conformational locks for organic HTMs ZS13, which shows good charge transfer properties, thermal stability and passivation function. Perovskite solar cells using ZS13 as doped HTM yield a champion device efficiency of 24.39 % with good thermal and light stability.

Abstract

Organic semiconductors with noncovalently conformational locks (OSNCs) are promising building blocks for hole-transporting materials (HTMs). However, lack of satisfied neighboring building blocks negatively impacts the optoelectronic properties of OSNCs-based HTMs and imperils the stability of perovskite solar cells (PSCs). To address this limitation, we introduce the benzothieno[3,2-b]thiophene (BTT) to construct a new OSNC, and the resulting HTM ZS13 shows improved intermolecular charge extraction/transport properties, proper energy level, efficient surface passivation effect. Consequently, the champion devices based on doped ZS13 yield an efficiency of 24.39 % and 20.95 % for aperture areas of 0.1 and 1.01 cm², respectively. Furthermore, ZS13 shows good thermal stability and the capability of inhibiting I⁻ ion migration, thus, leading to enhanced device stability. The success in neighboring-group engineering can triggered a strong interest in developing thienoacene-based OSNCs toward efficient and stable PSCs.

Introducing 2,3,5-Trichlorobenzaldehyde (3Cl-BZH) into the organic salt perovskite precursor enhances stability by curbing byproduct formation. The chemical interaction with formamidinium slows organic ion release, delaying perovskite film crystallization. Conventional annealing yields a champion efficiency of 24.08%, attributed to 3Cl-BZH's defect passivation. Remarkably, the perovskite solar cells maintain 22.01% efficiency with an ultrawide, 240 h annealing window for wet perovskite films in air.

Abstract

Perovskite solar cells (PSCs) have attracted extensive attention in the photovoltaic field, with their highest power conversion efficiency (PCE) reaching 26%. However, the commercialization of PSCs is severely hindered by the instability of precursor solutions and the narrow annealing window for perovskite films. Here, 2,3,5-trichlorobenzaldehyde (3Cl-BZH) is introduced into the organic salt precursor solution to eliminate excess organic amines through Schiff-base reactions, avoiding subsequent irreversible amine-cation reaction of formamidine-methylammonium (FA-MA⁺) and improve the stability of the precursor solution. Meanwhile, the chemical interaction between C═O group of 3Cl-BZH and formamidinium (FA⁺) in the perovskite precursor contributes to the slow release of organic ions, which reduces the reaction rate between organic salt and PbI₂, retarding the crystallization of perovskite film. The PSCs with a conventional annealing process achieve a champion efficiency of 24.08%, which derives from the defect passivation effect of 3Cl-BZH. The PSCs with an ultrawide annealing window of 240 h for wet perovskite film in the air still maintain an efficiency of 22.01%. The aging-resistant precursor and ultrawide annealing window are beneficial for reproducible, efficient, and low-cost PSCs, which brings great prospects for the commercialization of PSCs.

The conventional layer-by-layer (LbL) all-polymer solar cells (APSCs) prepared with polymer PM6 as donor and polymer PY-DT as acceptor exhibit an optimized power conversion efficiency of 17.24%, resulting from the efficient charge transport and exciton utilization. The energy transfer from PM6 to PY-DT and the self-absorption effect of PM6 effectively prolong the diffusion distance of photogenerated excitons and improve exciton utilization efficiency.

Series of bulk heterojunction (BHJ) and layer-by-layer (LbL) all-polymer solar cells (APSCs) were prepared with polymer PM6 as donor and polymer PY-DT as acceptor based on conventional and inverted configuration. Benefiting from the sequential deposition strategy, the good vertical phase separation and more ordered molecular arrangement can be formed in the LbL APSCs. The conventional LbL APSCs exhibit an optimized power conversion efficiency (PCE) of 17.24% with a relatively large short circuit current density of 23.83 mA cm⁻² and fill factor of 74.60%, photogenerated excitons near the indium tin oxide electrode can be efficiently utilized through energy transfer from PM6 to PY-DT and the self-absorption effect of PM6 for its long exciton diffuse distance. The 17.24% PCE of conventional LbL APSCs is higher than 16.72% of conventional BHJ APSCs, 14.59% of inverted BHJ APSCs and 12.41% of inverted LbL APSCs. The rather low PCE of 12.41% for the inverted LbL APSCs further indicates that the energy transfer from donor to acceptor and self-absorption effect of donor should play a vital role in determining the performance of LbL APSCs. This work provides more insights on the exciton and carrier dynamic process in sequentially deposited active layer, providing more guidance for preparing efficient LbL APSCs.

A series of volatile benzene additives is developed by crossbreeding effect of fluorination and bromination for improving blend morphology and charge extraction. A champion power conversion efficiency of 19.43% is realized finally in ternary blend organic solar cells.

Abstract

Employing volatile solid additives have emerged as a promising method to optimize the morphology and improve the performance of organic solar cells (OSCs). However, principles governing the efficient design of solid additives remain elusive. Herein, the programmed fluorination and/or bromination on benzene core to develop efficient additives for OSCs is reported. The programmed fluorination and/or bromination endow the five halogen benzene derivatives, 1,3,5-trifluorobenzene, hexafluorobenzene, 1,3,5-tribromo-2,4,6-trifluorobenzene (TFTB), 1,3,5-tribromobenzene, and hexabromobenzene, with different melting and boiling points, volatility, as well as interactions with the host blend. Studies indicate that the additives with extremely high and low volatility are almost powerless and even detrimental to the morphology evolution. Among them, the combination of fluorine and bromine atoms on TFTB not only enables the more appropriate m.p./b.p. and volatility, but also exerts stronger molecular interactions with the host blend, giving rise to higher ordered molecular packing and more favorable morphology. Importantly, TFTB exhibits good universality to optimize the performances of OSCs with high power conversion efficiencies (PCEs; over 18%) in a group of binary blend systems, and an impressive PCE of 19.43% in the ternary PBTz-F:PM6:L8-BO system.

A comprehensive analysis of device physics of high-performance perovskite solar cells (PSCs) is conducted before and after a short-pulse 170 keV proton irradiation with a fluence of up to 10¹³ p cm⁻². The findings highlight the remarkable resilience of multicomponent PSCs to extreme high-intensity short-pulse proton irradiation, which exceeds harsh space conditions and whose effect on PSCs is not investigated previously.

Abstract

This work investigates the radiation resistance of high-performance multi-component perovskite solar cells (PSCs) for the first time under extreme short-pulse proton irradiation conditions. The devices are subjected to high-intensity 170 keV pulsed (150 ns) proton irradiation, with a fluence of up to 10¹³ p cm^−2, corresponding to ≈30 years of operation at low Earth orbit. A complex material characterization of the perovskite active layer and device physics analysis of the PSCs before and after short-pulse proton irradiation is conducted. The obtained results indicate that the photovoltaic performance of the solar cells experiences a slight deterioration up to 20 % and 50 % following the low 2 × 10¹² p cm⁻² and high 1 × 10¹³ p cm⁻² proton fluences, respectively, due to increased non-radiative recombination losses. The findings reveal that multi-component PSCs are immune even to extreme high-intense short-pulse proton irradiation, which exceeds harsh space conditions, including intense coronal ejection events usually associated with solar flares.

A room-temperature molten salt, dimethylamine formate (DMAFa) is introduced into perovskite precursor solution to regulate the crystallization process of CsPbI₃ films. DMAFa can coordinate with Pb²⁺ as HCOO⁻-Pb²⁺ in the early stages, then HCOO⁻-Pb²⁺ gradually gets displaced by I⁻-Pb²⁺, thus delays the crystallization rate. Finally, excellent photovoltaic performance is obtained.

Abstract

Defects within perovskite have been known to act as the nonradiative recombination centers, negatively impacting the carrier transport, which degrades the photovoltaic performance of perovskite solar cells (PSCs). Therefore, preparing a high-quality perovskite film is of vital significance. To this end, a room-temperature molten salt, dimethylamine formate (DMAFa), is introduced into perovskite precursor solution to regulate the crystallization process of CsPbI₃ films. DMAFa can coordinate with Pb²⁺ as HCOO⁻-Pb²⁺ in the early stages, then HCOO⁻-Pb²⁺ is gradually displaced by I⁻-Pb²⁺ due to its decomposition during the subsequent annealing, thus delaying the crystallization rate, meanwhile, the DMA⁺ can interact with the uncoordinated Pb²⁺ to passivate defects of perovskite films, thereby, forming a high-quality CsPbI₃ film with large grain size and low-defect density. As a result of this strategy, the power conversion efficiency is increased to 20.40%, and the open-circuit voltage is up to 1.21 V. These findings indicate that the introduction of DMAFa offers a fundamental way to achieve high-performance CsPbI₃ PSCs.

A crystal orientation regulation strategy by introducing dodecyl-benzene-sulfonic-acid as an additive in perovskite precursors is proposed, which significantly promotes the desired (001) crystal orientation. Thus, opaque and semitransparent 1.66 eV bandgap methylamine-free perovskite solar cells realize efficiencies of 22.40% and 20.13%, respectively. Furthermore, four-terminal all-perovskite tandem cells deliver a remarkable efficiency of 28.06%.

Abstract

Wide-bandgap (WBG) perovskite solar cells have attracted considerable interest for their potential applications in tandem solar cells. However, the predominant obstacles impeding their widespread adoption are substantial open-circuit voltage (V _OC) deficit and severe photo-induced halide segregation. To tackle these challenges, a crystal orientation regulation strategy by introducing dodecyl-benzene-sulfonic-acid as an additive in perovskite precursors is proposed. This method significantly promotes the desired crystal orientation, passivates defects, and mitigates photo-induced halide phase segregation in perovskite films, leading to substantially reduced nonradiative recombination, minimized V _OC deficits, and enhanced operational stability of the devices. The resulting 1.66 eV bandgap methylamine-free perovskite solar cells achieve a remarkable power conversion efficiency (PCE) of 22.40% (certified at 21.97%), with the smallest V _OC deficit recorded at 0.39 V. Furthermore, the fabricated semitransparent WBG devices exhibit a competitive PCE of 20.13%. Consequently, four-terminal tandem cells comprising WBG perovskite top cells and 1.25 eV bandgap perovskite bottom cells showcase an impressive PCE of 28.06% (stabilized 27.92%), demonstrating great potential for efficient multijunction tandem solar cell applications.

Nature Energy, Published online: 13 November 2023; doi:10.1038/s41560-023-01400-x

Publication date: February 2024

Source: Journal of Energy Chemistry, Volume 89

Author(s): Fazheng Qiu, Ming-Hua Li, Jinpeng Wu, Jin-Song Hu

Publication date: 20 December 2023

Source: Joule, Volume 7, Issue 12

Author(s): Zhijun Ren, Zewei Cui, Xiaoyu Shi, Lingyuan Wang, Yunjie Dou, Feifei Wang, Haoran Lin, He Yan, Shangshang Chen

A multifunctional Lewis-base 4-bromo-2,6-diaminopyridine (4BrDP) is employed in tin perovskite precursor to inhibit the formation of I₃ ⁻ and related defect density by strong coordinate bonding and N─H···I hydrogen bonding. These benefits deliver an efficiency of 13.40% with remarkable improvement in both open-circuit voltage (V _oc) of 881 mV and fill factor (FF) of 71.26% in tin halide perovskite solar cells.

Abstract

Tin halide perovskite solar cells (PSCs) are regarded as the most promising lead-free alternatives for photovoltaic applications. However, they still suffer from uncompetitive photovoltaic performance because of the facile Sn²⁺ oxidation and Sn-related defects. Herein, a defect and carrier management strategy by using diaminopyridine (DP) and 4-bromo-2,6-diaminopyridine (4BrDP) as multifunctional additives for tin halide perovskites is reported. Both DP and 4BrDP induced strong interaction with tin perovskites by coordinate bonding and N─H···I hydrogen bonding, which greatly suppresses the micro-strain and Urbach energy of tin halide perovskite films. The strong hydrogen bonding inhibits the formation of I₃ ⁻ and related defect density. Meanwhile, the electron-donor species of halogen bond in 4BrDP provides higher reactivity of 2 and 6 sites, which indicates stronger passivation ability with tin halide perovskites. These advances enable a champion power conversion efficiency (PCE) of 13.40% in 4BrDP-processed devices with remarkable improvement in both open-circuit voltage (V _oc) of 881 mV and fill factor (FF) of 71.26%. The 4BrDP devices retain 91% and 82% of the pristine PCE after 2000 h storage in N₂ atmosphere and 1000 h under 85 °C, respectively. Therefore, this work provides new insight into molecular design for high-performance and stable lead-free optoelectronics.

Calculation and synthesis of a variety of pseudo-para-substituted [2.2]paracyclophanes for use as hole transport layers is presented. Functionalization with methoxy and tert-butyl substituted donor groups allows tuning of the ionization potential. The novel compounds achieve competitive hole mobility and the most promising material is estimated to cost only a third of the standard 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)−9,9′-spirobifluorene thanks to the facile synthesis via double CH activation.

Abstract

2,2′,7,7′-Tetrakis(N,N-di-p-methoxyphenylamine)−9,9′-spirobifluorene (spiro-OMeTAD) is the prevalent hole transport layer in perovskite solar cells (PSCs) with regular device architecture. Yet, its spirobifluorene core and multistep synthesis make it rather expensive. For the further technological success of PSCs, novel scalable and inexpensive alternative hole transport layers are needed. Herein, a study of the structure-property relations of pseudo-para-substituted [2.2]paracyclophanes is presented. Eight different hole transport materials are synthesized via double CH activation, eliminating metal-containing substituents for cross-coupling reactions. The ionization potentials (IPs) of the disubstituted paracyclophanes (DiPCPs) are examined by photoelectron spectroscopy in air, cyclic voltammetry and theoretical calculations. Through variation of donor groups and π-linkers, IPs that span a range from 5.14 to 5.86 eV are achieved, demonstrating high customizability. From the eight novel materials, five showed good solubility and are implemented into PSCs. The solar cells with a hole transport layer of undoped 4,16-di(4-(2-thienyl)-N,N-bis(4-methoxyphenyl)aniline)[2.2]paracyclophane (DiPCP-2) exhibit a power conversion efficiency of 12.7% ± 0.4%. The facile synthesis of DiPCP-2 enables an estimated cost reduction by two thirds compared to spiro-OMeTAD.

The existence of hole transfer channels at the chemical interface in dilute PBDB-T-b-PTY6 block copolymer films is rigorously demonstrated. It is found that the intramolecular hole transfer rate is approximately an order of magnitude higher than the intermolecular one in the traditional blend films. The intramolecular channel contributes significantly to the hole transfer efficiency (30.5%), comparable to the intermolecular channel in PBDB-T-b-PTY6 films.

Abstract

The study reports for the first time on the ultrafast dynamics of charge transfer (CT) and exciton dissociation in block copolymer PBDB-T-b-PTY6-based state-of-the-art single-material organic solar cells (SMOSCs). From the transient absorption spectroscopy of the dilute PBDB-T-b-PTY6 in the insulating polystyrene, exciton dissociation and hole transfer (HT) processes at the intramolecular interface of covalent linkage between the donor and acceptor segment are achieved. In comparison to the charge generation in blend PBDB-T:PTY6 films, it is found that the HT rate in the isolated block copolymer chain via the intramolecular channel is approximately an order of magnitude higher than that via the intermolecular channel. Much faster exciton dissociation in the dilute PBDB-T-b-PTY6 film than in the blend film from electro-absorption and polaron-absorption signals is also verified. The intrachain chemical interface in the block copolymer is thus more conducive to the HT path than the traditional interface in the bulk heterojunction. Moreover, though the PBDB-T-b-PTY6 film has weak molecular ordering, its overall CT efficiency is comparable to that of the PBDB-T:PTY6 film. These findings portend that further molecular design with optimized ordering toward fast intramolecular exciton dissociation may contribute to SMOSCs with higher power conversion efficiency.

A fully non-fused acceptor R4T-1 was designed via macrocyclic encapsulation on the simple tetrathiophene, which achieves conformational unicity, eliminates intermolecular electronic cross-communication at the center and guarantees the formation of efficient charge transport channels. Thus, an impressive power conversion efficiency (PCE) of 15.10 % with a significantly enhanced short-circuit current density (J _sc) of 25.48 mA/cm² was accomplished.

Abstract

Non-fullerene acceptors have shown great promise for organic solar cells (OSCs). However, challenges in achieving high efficiency molecular system with conformational unicity and effective molecular stacking remain. In this study, we present a new design of non-fused tetrathiophene acceptor R4T-1 via employing the encapsulation of tetrathiophene with macrocyclic ring. The single crystal structure analysis reveals that cyclic alkyl side chains can perfectly encapsulate the central part of molecule and generate a conformational stable and planar molecular backbone. Whereas, the control 4T-5 without the encapsulation restriction displays cis- and twisted conformation. As a result, R4T-1 based OSCs achieved an outstanding power conversion efficiency (PCE) exceeding 15.10 % with a high short-circuit current density (J _sc) of 25.48 mA/cm², which is significantly improved by ≈30 % in relative to that of the control. Our findings demonstrate that the macrocyclic encapsulation strategy could assist fully non-fused electron acceptors (FNEAs) to achieve a high photovoltaic performance and pave a new way for FNEAs design.

The study systematically employed and examined three nanoscale thiol-functionalized UiO-66-type Zr-based MOFs (UiO-66-(SH)₂, UiO-66-MSA, and UiO-66-DMSA) in perovskite solar cells and provided a detailed and in-depth discussion on the formation mechanism of UiO-66-(SH)₂-assisted perovskite film upon in situ GIWAXS performed during the annealing process. The final device improved opto-electronic properties by over 24%.

Abstract

Metal–organic frameworks (MOFs) have been investigated recently in perovskite photovoltaics owing to their potential to boost optoelectronic performance and device stability. However, the impact of variations in the MOF side chain on perovskite characteristics and the mechanism of MOF/perovskite film formation remains unclear. In this study, three nanoscale thiol-functionalized UiO-66-type Zr-based MOFs (UiO-66-(SH)₂, UiO-66-MSA, and UiO-66-DMSA) are systematically employed and examined in perovskite solar cells (PSCs). Among these MOFs, UiO-66-(SH)₂, with its rigid organic ligands, exhibited a strong interaction with perovskite materials with more efficient suppression of perovskite vacancy defects. More importantly, A detailed and in-depth discussion is provided on the formation mechanism of UiO-66-(SH)₂-assisted perovskite film upon in situ GIWAXS performed during the annealing process. The incorporation of UiO-66-(SH)₂ additives substantially facilitates the conversion of PbI₂ into the perovskite phase, prolongs the duration of stage I, and induces a delayed phase transformation pathway. Consequently, the UiO-66-(SH)₂-assisted device demonstrates reduced defect density and superior optoelectronic properties with optimized power conversion efficiency of 24.09% and enhanced long-term stability under ambient environment and continuous light illumination conditions. This study acts as a helpful design guide for desired MOF/perovskite structures, enabling further advancements in MOF/perovskite optoelectronic devices.

A novel amphoteric semiconductor (PHAAT) is introduced into the Sn perovskite surface to simultaneously manage various shallow and deep-level related defects, and induce the formation of p-n homojunction on the shallow surface to promote electron extraction, which increases the power conversion efficiency to 13.94%.

Abstract

Severe nonradiative recombination and open-circuit voltage loss triggered by high-density interface defects greatly restrict the continuous improvement of Sn-based perovskite solar cells (Sn-PVSCs). Herein, a novel amphoteric semiconductor, O-pivaloylhydroxylammonium trifluoromethanesulfonate (PHAAT), is developed to manage interface defects and carrier dynamics of Sn-PVSCs. The amphiphilic ionic modulators containing multiple Lewis-base functional groups can synergistically passivate anionic and cationic defects while coordinating with uncoordinated Sn²⁺ to compensate for surface charge and alleviate the Sn²⁺ oxidation. Especially, the sulfonate anions raise the energy barrier of surface oxidation, relieve lattice distortion, and inhibit nonradiative recombination by passivating Sn-related and I-related deep-level defects. Furthermore, the strong coupling between PHAAT and Sn perovskite induces the transition of the surface electronic state from p-type to n-type, thus creating an extra back-surface field to accelerate electron extraction. Consequently, the PHAAT-treated device exhibits a champion efficiency of 13.94% with negligible hysteresis. The device without any encapsulation maintains 94.7% of its initial PCE after 2000 h of storage and 91.6% of its initial PCE after 1000 h of continuous illumination. This work provides a reliable strategy to passivate interface defects and construct p-n homojunction to realize efficient and stable Sn-based perovskite photovoltaic devices.

This work presents a new strategy to obtain high-performance CsPbI₃ perovskite via using an extraordinary antisolvent, ethyl cyanoformate (EC). The multiple functions of EC improve the PCE of P3HT-based CsPbI₃ PSCs to 18.46 % from 17.33 %. The PCE is further increased to 19.15 % when doped P3HT with 4-Cyano-4′-pentylbipheny (5CB) according to the previous work.

Abstract

Surface defects are always a severe problem in inorganic perovskite, superadding the mismatch of energy level between Poly(3-hexylthiophene) (P3HT) hole transport layer (HTL) and CsPbI₃ perovskite. All these issues result in large losses in open-circuit voltage (V _oc) and fill factor (FF), and thus, CsPbI₃ perovskites solar cells (PSCs) based on P3HT HTL commonly show a lower power conversion efficiency (PCE). Herein, an extraordinary antisolvent engineering is proposed by ethyl cyanoformate (EC), that regulates the crystallization progress to improve the quality of CsPbI₃ perovskite film. Concomitantly, residual EC passivates the uncoordinated Pb²⁺ defects by synergistical chemical interaction of C≡N and C═O groups, and energy level arrangement at the CsPbI₃/P3HT interface is also optimized. As a result, the PCE of P3HT-based CsPbI₃ PSC is improved to 18.46% from 17.33% of the control device. The unencapsulated CsPbI₃ PSCs show enhanced moisture stability and fine operational stability. The work reveals that EC is an extraordinary antisolvent, exhibiting a synergistic strategy in many aspects for obtaining high-performance P3HT-based CsPbI₃ PSCs. Furthermore, P3HT is doped with a small amount of 4-Cyano-4′-pentylbipheny (5CB), and thus the PCE of PSC is increased to 19.15% and its humidity stability is significantly improved.

Nature Energy, Published online: 09 November 2023; doi:10.1038/s41560-023-01382-w

A class of novel halide substituted ammonium salts are designed and synthesized to modify the buried interface as well as the perovskite crystallization of flexible perovskite solar cells. A stabilized efficiency of 20.3% along with an improved operational stability is achieved.

Abstract

Low-temperature solution processing of the perovskite layer enables the fabrication of flexible devices. However, the performance of flexible perovskite solar cells (f-PSCs) lags far behind their rigid counterpart in terms of efficiency and stability. Emerging evidence demonstrates that the quality of the buried interface between perovskite and transporting layer underneath is the key point. Herein, a class of novel halide substituted ammonium salts, i.e., n-bromophenethylammonium (n-Br-PEAX, n = 2 or 4, X = Cl or Br) are designed and synthesized to modify the buried interface as well as the perovskite crystallization of f-PSCs. It is found that the ammonium salt with rational design molecular structure can modify the crystallization speed of perovskite, leading to the formation of a compact and uniform morphology without nanovoids at the interface. As a result, the efficiency of f-PSCs is improved from 15.4% to 20.2%. Moreover, the modified devices without encapsulation retain 86% of their initial performance after 1000 h of aging at ambient conditions and 87% after 290 h of continuous operation.

This work implements a sequential interface engineering (SIE) strategy that involves the deposition of ethylenediamine diiodide followed by sequential deposition of 4-Fluoro-Phenethylammonium chloride on perovskite film. This technique synergistically narrows the conduction band offset and reduces recombination velocity at the perovskite/C₆₀ interface. Based on the SIE strategy, the PCE of 29.6% for a 1 cm² monolithic perovskite/silicon tandem cell is achieved.

Abstract

Wide-bandgap (WBG) perovskite solar cells hold tremendous potential for realizing efficient tandem solar cells. However, nonradiative recombination and carrier transport losses occurring at the perovskite/electron-selective contact (e.g. C₆₀) interface present significant obstacles in approaching their theoretical efficiency limit. To address this, a sequential interface engineering (SIE) strategy that involves the deposition of ethylenediamine diiodide (EDAI₂) followed by sequential deposition of 4-Fluoro-Phenethylammonium chloride (4F-PEACl) is implemented. The SIE technique synergistically narrows the conduction band offset and reduces recombination velocity at the perovskite/C₆₀ interface. The best-performing WBG perovskite solar cell (1.67 eV) delivers a power conversion efficiency (PCE) of 21.8% and an impressive open-circuit voltage of 1.262 V. Moreover, through integration with double-textured silicon featuring submicrometer pyramid structures, a stabilized PCE of 29.6% is attained for a 1 cm² monolithic perovskite/silicon tandem cell (certified PCE of 29.0%).

Ternary polymerization strategy is employed to manipulate the vertical phase separation in pseudoplanar heterojunction (PPHJ) organic solar cells (OSCs). The terpolymer DL1, with enhanced solubility, partial edge-on orientation, and high crystallinity, endows DL1/Y6 PPHJ blend film with the optimized vertical phase separation. Therefore, DL1/Y6 based PPHJ OSCs afford an impressive PCE of 19.10%, which is the record for terpolymer donors.

Abstract

Controlling vertical phase separation of the active layer to enable efficient exciton dissociation and charge carrier transport is crucial to boost power conversion efficiencies (PCEs) of pseudoplanar heterojunction (PPHJ) organic solar cells (OSCs). However, how to optimize the vertical phase separation of PPHJ OSCs via molecule design is rarely reported yet. Herein, ternary polymerization strategy is employed to develop a series of polymer donors, DL1-DL4, and regulate their solubility, molecular aggregation, molecular orientation, and miscibility, thus efficiently manipulating vertical phase separation in PPHJ OSCs. Among them, DL1 not only has enhanced solubility, inhibited molecular aggregation and partial edge-on orientation to facilitate acceptor molecules, Y6, to permeate into polymer layer and increase donor/acceptor interfaces, but also sustains high crystallinity and appropriate miscibility with Y6 to acquire ordered molecular packing, thus achieving optimized vertical phase separation to well juggle exciton dissociation and charge transport in PPHJ devices. Therefore, DL1/Y6 based PPHJ OSCs gain the best exciton dissociation probability, highest charge carrier mobilities and weakest charge recombination, and thus afford an impressive PCE of 19.10%, which is the record value for terpolymer donors. It demonstrates that ternary polymerization is an efficient method to optimize vertical phase separation in PPHJ OSCs for high PCEs.

Directional defects management in polycrystalline perovskite film with inorganic passivator is highly demanded while yet realized for fabricating efficient and stable perovskite solar cells (PSCs). Here, we develop a directional passivation strategy employing a two-dimensional (2D) material, Cu-(4-mercaptophenol) (Cu-HBT), as a passivator precursor. Cu-HBT combines the merits of the targeted modification from organic passivator and excellent stability offered by inorganic passivator. Featuring with dense organic functional motifs on its surfaces, Cu-HBT has the capability to “find” and fasten to the Pb defect sites in perovskites through coordination interactions during a spin-coating process. During subsequent annealing treatment, the organic functional motifs cleave from Cu-HBT and convert in-situ into p-type semiconductors, Cu2S and PbS. The resultant Cu2S and PbS not only serve as stable inorganic passivators on the perovskite surface, significantly enhancing cell stability, but also facilitate efficient charge extraction and transport, resulting in an impressive efficiency of up to 23.5%. This work contributes a new defect management strategy by directionally yielding the stable inorganic passivators for highly efficient and stable PSCs.

A new ionic liquid crystal (ILC, 1-Dodecyl-3-methylimidazolium tetrafluoroborate) was developed to modify buried interface of perovskite solar cells (PSC). The ILC promotes a preferential growth of perovskite along [001] direction and exhibits strong interaction with perovskite to passivate defects. The ILC-modified PSC delivers an efficiency of 24.92 % and maintains 94 % of the original value after storage in ambient for 3000 h.

Abstract

It is found that the disordered growth of bottom perovskite film deteriorates the buried interface of perovskite solar cells (PSCs), so developing a new material to modify the buried interface for regulating the crystal growth and defect passivation is an effective approach for improving the photovoltaic performance of PSCs. Here, we developed a new ionic liquid crystal (ILC, 1-Dodecyl-3-methylimidazolium tetrafluoroborate) as both crystal regulator and defect passivator to modify the buried interface of PSCs. The high lattice matching between this ILC and perovskite promotes preferential growth of perovskite film along [001] direction, while the oriented ILC with mesomorphic phase has a strong chemical interaction with perovskite to passivate the interface defect, as a result, the modified buried interface exhibits suppressed defects, improved band alignment, reduced nonradiative recombination losses, and enhanced charge extraction. The ILC-modified PSC delivers a power conversion efficiency of 24.92 % and maintains 94 % of the original value after storage in ambient for 3000 h.