Yingzhi Jin

A wide-bandgap guest material is designed, synthesized, and used as the guest material for ternary polymer solar cells to improve the power conversion efficiency and reduce the energy loss.

The rational design of guest photovoltaic materials (the third components) for enhancing the power conversion efficiency (PCE) of ternary polymer solar cells (PSCs) is a challenge. In this work, a large-bandgap material ((5Z,5′Z)-5,5′-(((4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(2,5-difluoro-4,1-phenylene))bis(methanylylidene))bis(3-ethyl-2-thioxothiazolidin-4-one, IBR-F) is designed, synthesized, and used as the guest material for ternary PSCs to improve the PCE and reduce the energy loss. IBR-F possesses a larger energy bandgap of 2.04 eV and a deeper highest occupied molecular orbital (HOMO) level compared to PM6, as well as exhibiting good miscibility with PM6. Thus, the HOMO level is effectively downshifted when blending PM6 with IBR-F, which is in favor of obtaining a higher open-circuit voltage (V _oc). Meanwhile, the incorporation of IBR-F into the PM6:Y6 blend can maintain the well-developed bulk-heterojunction morphological properties of the host blend without extra thermal annealing and improve the charge dissociation and collection efficiencies. As a result, the ternary PSC based on PM6:IBR-F:Y6 (1:0.2:1.2 w/w) demonstrates a higher V _oc of 0.887 V and a reduced energy loss of 0.55 eV compared to the binary device based on PM6:Y6 (1:1.2 w/w) with a V _oc of 0.840 V and energy loss of 0.59 eV, delivering an improved PCE of 17.15%.

1) Recent progress in semitransparent organic solar cells (ST-OSCs) is summarized, 2) multifunctional applications of ST-OSCs are discussed, 3) challenges for future developments of ST-OSCs are proposed, and 4) outlooks of promising future research directions for ST-OSCs are presented.

Opaque and semitransparent organic solar cells (ST-OSCs) have made tremendous progress in recent years. Efficiencies over 18% and 13% have been demonstrated for opaque ST-OSCs, respectively. OSCs do not contain unfavorable elements such as lead, which makes them available for broader potential applications when compared with other lead-contained thin-film solar cells. There has also been tremendous progress in the ST-OSCs, which makes them extremely appealing for promising emerging applications such as building-integrated photovoltaics. Herein, a progress review in the field is presented for helping the researchers better understand ST-OSCs and further realize their potentials. Recent strategies in ST-OSCs based on three perspectives are summarized, including electrode engineering, active layer engineering, and device engineering. A wide range of applications where ST-OSCs can be used is discussed and challenges for future developments of ST-OSCs are pointed out. Finally, the outlook for promising future research directions is presented.

A series of halogen-free polymer donors is developed by the incorporation of the diketopyrrolopyrrole unit into the paradigm PBDB-T backbone. The optimal P75-based device shows the best power conversion efficiency of 10.28%. A slight addition of PC₇₁BM into the blend is found to further generate finer phase-separated domains and thus further increase the efficiency up to 12.20%.

High-performance polymer donors when paired with nonfullerene acceptors are mainly limited to flanking halogenated benzodithiophene (BDT)-based π-conjugated copolymers, which however involve complex synthetic procedures. Herein, a series of halogen-free polymer donors that link BDT moiety with two highly electron-deficient benzodithiophene-dione (BDD) and diketopyrrolopyrrole (DPP) units with various molar ratios is developed. Compared with the benchmark PBDB-T donor containing BDD unit, additional incorporation of a stronger electron-negative DPP unit markedly lowers frontier molecular orbital levels and extends optical absorption, potentially leading to simultaneously enhanced V _OC and J _SC in organic solar cells. A remarkable power conversion efficiency (PCE) of 10.28% is thus obtained in the optimal P75 (BDD : DPP = 3:1 mol%) and Y6 blend cells in comparison with the reference PBDB-T:Y6 (9.20%). A slight addition of PC₇₁BM into the blend is found to further generate finer phase-separated domains and thus increase the best efficiency up to 12.20%. The subtly critical roles of PC₇₁BM are determined by transient absorption measurements on both thin-film and in situ devices to be the prolonged free charge carrier lifetime and the shallow charge transfer states, which enhance J _SC and fill factor in the device, respectively.

The polymer acceptor PJ1 shows strong aggregation in all-polymer solar cells when processed with o-xylene solvent. Herein, another polymer acceptor PJ2 with a similar backbone to PJ1 but much weaker aggregation ability is designed to suppress the aggregation of PJ1. Eventually, a highly efficient ternary device with the best efficiency of 14.28% is obtained.

Rapid developments in material design have led to significant breakthroughs in the power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs) in recent years. However, most of these devices are processed using halogenated solvents. Here, nonhalogenated solvent o-xylene (o-XY)-processed all-PSCs based on PBDB-T:PJ1 are studied. Interestingly, it is found that the efficiency of the all-PSCs can be greatly improved to 14.34% by simply increasing the spin-coating speed during device processing. Careful studies reveal that this improvement could be attributed to the stronger centrifugal force (resulting from a higher spin-coating speed), shorten the film formation time, and inhibit the excessive aggregation of PJ1. Consequently, a blend film with more reasonable domain size is formed. Based on these findings, another polymer acceptor PJ2, which bears a similar backbone to PJ1 but contains an additional thiophene spacer, is designed. PJ2 exhibits a much weaker aggregation ability and is used as a compatibilizer to improve the miscibility between the PBDB-T and PJ1. Eventually, PBDB-T:PJ1:PJ2-based ternary all-PSCs with a best PCE of 14.28% but processed under more mild conditions are obtained. These results may provide guidelines for future industrial fabrication of large-area all-PSCs.

A series of isomeric unfused-ring electron acceptors (UREAs) involving noncovalent conformational locks are synthesized and characterized. Through the systematic investigation about the regioisomeric effects on the molecular properties, blend morphologies, and device performances, introducing isomeric moieties into molecular design is considered as an effective strategy for exploring more efficient UREAs.

Isomeric effects play a crucial role in regulating electronic properties, molecular packing, and device performance of organic semiconductors. Herein, a series of unfused-ring electron acceptor (UREA) regioisomers (NOF-1, NOF-2, and NOF-3), which are constructed using 2,6-α-, 1,5-β-, and 3,7-β-type naphthalene cores, are successfully synthesized and characterized. The regioisomeric effects on geometries, photophysics, electrical properties, molecular packing behaviors, charge transport properties, blend film morphologies, and photovoltaic performance are systematically studied. As a result, the PBDB-T:NOF-3-based device delivers a power conversion efficiency (PCE) of 11.58% due to its more balanced charge mobility, efficient exciton dissociation, less charge recombination, and favorable film morphology. These findings encourage further attention to the regioisomeric effects to design high-performance UREAs.

Interfacial reactions between the perovskite emitters and the interlayers are detrimental to the operational stability of the perovskite light-emitting diodes. Incorporating dicarboxylic acids into the precursor efficiently eliminates reactive organic ingredients in the perovskite emitters through an in situ amidation process, which is catalyzed by the alkaline zinc oxide substrate underneath. The formed amides improve the stability of the perovskite emitters and the charge injection contacts, ensuing notably improved operational stability of the resulting perovskite light-emitting diodes.

Inorganic molecular clusters as a new type of hole transport material for organic solar cells (OSCs). We developed a facile method to enhance the conductivity without sacrificing its high WF nature; thus, the power conversion efficiency of OSC was enhanced from 0.25% to 17.3%. Besides, it can be processed by printing techniques, and 1.0 cm2 OSC is fabricated with 15.1%.

A patterned blade coating strategy is investigated to print non-fullerene based devices, with a PCE of 15.93%. The designed patterned blade enhances fluid flow to optimize morphology evolution kinetics for achieving an optimized morphology and device reproducibility. In addition, the versatility in large-area devices and other systems is also shown.

Abstract

Morphology evolution kinetics at multi-scale regime is a challenging problem which is critical for industrial fabrication of high-performance organic solar cells (OSCs). An innovative strategy utilizing a patterned blade to print non-fullerene (NF) based devices in ambient conditions is demonstrated. A specially designed patterned blade with micro-cylinder arrays exhibit a reasonable control over the fluid flow at high extensional and shear strain rate to enhance lateral mass transport during blade-coating. Comparison of patterned and normal blade in printing polymer:NF blend film at different speeds reveals interesting avenues to optimize the blend films morphology. Patterned blade printed PM6:Y6 films yield a PCE of 15.93% as compared to 14.55% from a normal blade. Through in situ and ex situ morphology characterization techniques, the use of patterned blades induce conformational changes in PM6 chains, enabling Y6 to crystallize faster and more efficiently. Such improved blend morphology enables favorable charge transfer and transport to realize superior device performance. A lower stick-slip effect at the macro-scale with the patterned blade results in a smoother film promoting device reproducibility. Applications in efficient large-scale devices, confirming the choice of patterned blade design are reported. The efforts collaborating device engineering, morphology evolution kinetics would enable reproducibility and eased commercialization of OSCs at large scale.

Two anthracene diimide polymers are synthesized and used as the acceptor in all-polymer solar cells (all-PSCs) for the first time, offering the best device efficiency of ≈7%. Moreover, general guidelines for screening donor/acceptor polymer combinations for all-PSCs are proposed by investigating their crystallinity and orientation behaviors in blend films.

Abstract

Electron-carrying polymers are highly desired for various optoelectronic applications but are still scarce. Herein, two anthracene diimide (ADI) polymers with thiophene and bithiophene as comonomer, respectively, are reported as electron acceptor materials in all-polymer solar cells (all-PSCs) for the first time. Effects of crystallinity and orientation of two polymer films as well as their blends with different donor polymers on photovoltaic properties are elaborately investigated by grazing-incidence X-ray diffraction and photo-induced force microscopy. It is found that molecular crystallinity and orientation determine the blend film morphology, and the similar high crystallinity and the same face-on orientation of donor and acceptor polymers are favorable for obtaining excellent photovoltaic performances. With this principle, a suitable donor polymer is singled out to match with the ADI acceptor polymer, offering an impressive efficiency of ≈7% for all-PSCs. This work demonstrates that ADI polymers are promising as acceptor materials and provides guidelines for screening donor and acceptor polymer combinations for all-PSCs.

Two novel triarylamine-based donor-acceptor copolymers featuring an imide-functionalized backbone are developed. Benefiting from the good energy level alignment, appropriate film morphology, and most importantly, improved hole mobility, the pristine PTTI-TPA based inverted perovskite solar cells achieve a high power conversion efficiency of up to 21% with negligible hysteresis and substantial stability.

Abstract

Dopant-free hole-transporting layers (HTLs) are highly desired for realizing efficient and stable perovskite solar cells (PVSCs), but only very few of them can enable power conversion efficiencies (PCEs) over 20%. Herein, two imide-functionalized triarylamine-based donor-acceptor (D-A) type copolymers, PBTI-TPA and PTTI-TPA, are developed and applied as dopant-free HTLs in inverted PVSCs. The combination of a classic redox-active triphenylamine donor unit and an electron-withdrawing oligothiophene imide co-unit with rigid and planar backbone furnishes the two polymers with quasi-planar backbone, suitable frontier molecular orbital (FMO) energy levels, favorable thermal stability, appropriate film morphology, and passivation effect. More importantly, the greatly improved hole mobility renders them as promising HTLs for PVSCs. As a result, the undoped PTTI-TPA-based inverted PVSCs deliver a remarkable PCE up to 21% as well as negligible hysteresis and substantial long-term stability, outperforming the devices based on PBTI-TPA and PTAA. The performance also represents one of the highest PCEs reported to date for PVSCs based on dopant-free polymeric HTLs. The results highlight the great potentials of oligothiophene imides for constructing donor-acceptor polymeric HTLs for enabling high-performance dopant-free PVSCs.

A hydrated MAPbI_{3− x} Cl _x thermochromic perovskite smart window is developed. The window demonstrates a passive and smart optical regulation ability between a transparent state and a tinted state. Most importantly, the window possesses a tunable low transition temperature, a controllable and narrow transition hysteresis width, and a short transition time, showing great potential for use in smart green buildings.

Abstract

Recently, organic hybrid halide perovskites have been found to show thermochromism with good optical performance, which can be applied in smart windows to reduce building energy consumption. However, these perovskites have shortcomings regarding their thermochromic performance, namely long transition time, high transition temperature, and large transition hysteresis width. In this study, a hydrated MAPbI_{3− x} Cl _x thermochromic perovskite smart window (H-MAPbI_{3− x} Cl _x TPSW) is proposed, which undergoes a reversible transition between a transparent state and a dark reddish-brown tinted state with a high solar modulation ability of 23.7%. Most importantly, the H-MAPbI_{3− x} Cl _x TPSW possesses a tunable low transition temperature of 29.4 to 51.4 °C, a controllable and narrow transition hysteresis width (7.7–13.2 °C) and a short transition time (1–4 min). Additionally, a mathematical model is developed to predict the transition temperature of the H-MAPbI_{3− x} Cl _x TPSW. A field test is also conducted, demonstrating that the H-MAPbI_{3− x} Cl _x TPSW fitted to a model house can reduce the indoor air temperature by 3.5 °C compared to using a quartz glass window. Overall, the H-MAPbI_{3− x} Cl _x TPSW can yield excellent optical properties, while simultaneously providing remarkable transition properties, making it potentially useful for a wide range of applications in energy-efficient buildings.

Two new orange–red thermally activated delayed fluorescence (TADF) materials, PzTDBA and PzDBA, are developed based on the acceptor–donor–acceptor configuration. The TADF devices fabricated with 5 wt% PzTDBA and PzDBA as emitting dopants show maximum external quantum efficiency (EQE) of 30.3% and 21.8% with extremely low roll‐off of 3.6% and 3.2% at 1000 cd m⁻². The high efficiency and low roll‐off is due to the high photoluminescence quantum yield (PLQY) and short delayed exciton lifetime.

Abstract

Two new orange–red thermally activated delayed fluorescence (TADF) materials, PzTDBA and PzDBA, are reported. These materials are designed based on the acceptor–donor–acceptor (A–D–A) configuration, containing rigid boron acceptors and dihydrophenazine donor moieties. These materials exhibit a small ΔE _ST of 0.05–0.06 eV, photoluminescence quantum yield (PLQY) as high as near unity, and short delayed exciton lifetime (τ_d) of less than 2.63 µs in 5 wt% doped film. Further, these materials show a high reverse intersystem crossing rate (k _risc) on the order of 10⁶ s⁻¹. The TADF devices fabricated with 5 wt% PzTDBA and PzDBA as emitting dopants show maximum EQE of 30.3% and 21.8% with extremely low roll‐off of 3.6% and 3.2% at 1000 cd m⁻² and electroluminescence (EL) maxima at 576 nm and 595 nm, respectively. The low roll‐off character of these materials is analyzed by using a roll‐off model and the exciton annihilation quenching rates are found to be suppressed by the fast k _risc and short delayed exciton lifetime. These devices show operating device lifetimes (LT₅₀) of 159 and 193 h at 1000 cd m⁻² for PzTDBA and PzDBA, respectively. The high efficiency and low roll‐off of these materials are attributed to the good electronic properties originatng from the A–D–A molecular configuration.

Ternary organic solar cells are fabricated, achieving a significant J _SC boost by virtue of an optimized crystalline feature with the formation of a eutectic mixture with better acceptor crystalline fibrils. The optimal morphology suppresses energetic disorder and recombination and increases charge transfer and transport, yielding a high efficiency of 17.84% with significant current boost.

Abstract

The intrinsic electronic properties of donor (D) and acceptor (A) materials in coupling with morphological features dictate the output in organic solar cells (OSCs). New physical properties of intimate eutectic mixing are used in nonfullerene-acceptor-based D–A₁–A₂ ternary blends to fine-tune the bulk heterojunction thin film morphology as well as their electronic properties. With enhanced thin film crystallinity and improved carrier transport, a significant J _SC amplification is achieved due to the formation of eutectic fibrillar lamellae and reduced defects state density. Material wise, aligned cascading energy levels with much larger driving force, and suppressed recombination channels confirm efficient charge transfer and transport, enabling an improved power conversion efficiency (PCE) of 17.84%. These results reveal the importance of utilizing specific material interactions to control the crystalline habit in blended films to form a well-suited morphology in guiding superior performances, which is of high demand in the next episode of OSC fabrication toward 20% PCE.