Organic semiconductors exhibit excellent defect passivation effects toward perovskite. However, due to their poor solubility in polar solvents, these materials are generally introduced into the perovskite film via interfacial engineering and therefore only effective in the interfacial region of perovskite solar cells (PSCs). Herein, we report a facile low-temperature nano-precipitation protocol to assemble organic semiconducting nanoparticles (NPs), which can be utilized to participate in the crystallization process of perovskite during solution casting. Being incorporated into the perovskite inks, these NPs exhibit favorable interactions with perovskite, not only modulates the crystallization process, yielding large and uniform crystal grains, but also provides comprehensive passivation across the film, reducing non-radiative recombination and enhancing conductivity. Inverted PSCs based on FA0.85Cs0.15PbI3 with ITCC-Br NPs achieved a power conversion efficiency of 23.81 %, compared to 21.38 % for the reference device. Furthermore, the devices maintained 83 % of their initial efficiency after 1200 h of exposure to ambient air, demonstrating enhanced stability.

Suppressing the dark current density in organic diodes is essential for developing practical consumer electronics such as in-door photovoltaics and photodetectors. While extensive research has explored dark current from thermodynamics and kinetics (of free and trapped charges) perspectives, a clear relationship between nanostructure and dark current remains elusive. In this contribution, the relationship between the structural/morphological order of non-fullerene acceptors (NFAs) with the dark current and shunts in their organic photodetectors (OPDs) is investigated. Starting with the state-of-the-art NFA C9-12 (BTP-eC9), we systematically tune the molecular structural symmetry and alkyl chain length. We find that unsymmetrizing the end groups and/or extending the alkyl chains of NFAs leads to swollen intermolecular packing in solid state, effectively suppressing microscopic shunting paths. Additionally, increasing alkyl chain length promotes more oriented intermolecular packing in the out-of-plane direction, reducing energetic disorder and consequently suppressing the thermal generation of dark charges. These combined benefits lead to a simultaneous suppression of both thermally activated diode current and shunt current in OPDs based on unsymmetrical non-fullerene acceptors with long alkyl chains.

As an exitonic photovoltaic device, organic solar cells (OSCs) consist of electron donating and accepting components in their photoactive layer, in which the molecular interactions between donor and acceptor can significantly affect the nanoscale morphology as well as the photovoltaic performance of OSCs. In this work, by diluting electron donor with electron acceptor having opposite electrostatic potentials to promote the structural order via strengthened intermolecular interactions, this study shows that polymeric diluent is more effective due to its long-ranged conjugated backbone compared with small molecular diluent. The ternary heterojunction made of C5-16:L8-BO binary acceptors diluted with D18 shows the strongest structural order, benefiting from the strong interactions between L8-BO and C5-16. The enhanced structural order within the photoactive layer prepared by layer-by-layer deposition of the diluted p-type and n-type heterojunctions contributes to enhanced light absorption, improved charge transport, and inhibited charge recombination. As the result, OSC based on D18 (PY-IT diluted)/L8-BO:C5-16 (D18 diluted) having donor and acceptor dual fibrils obtains an unprecedented power conversion efficiency of 21.0% (certified value of 20.25%), which is one of the highest certified PCE up to date.

Doctor-blading is a promising alternative for the large-area printing of organic solar cells (OSCs). However, the power conversion efficiencies (PCEs) of doctor-bladed OSCs are still lower than those of their spin-cast counterparts. This is mainly caused by the prolonged molecular organization time during which excessive aggregation can be encouraged. In this work, a post-treatment using nitrogen gas to blow the backside of the photoactive layer, i.e., the ITO glass side, was utilized to modulate the aggregation growth after blade-coating from a nonhalogenated solvent. A range of morphological measurements reveal that gas-blowing suppresses excessive aggregation of nonfullerene acceptors. As a result, gas-blowing treated PM6:BTP-eC9 OSCs obtained a maximum PCE of 19.0%, which is among the highest values of blade-coated OSCs. Moreover, this morphology transformation also drives the photoactive layer toward the thermodynamic equilibrium state, reducing free volume in the photoactive layer and contributing to better device stabilities.

Defects at the bulk and grain boundaries of perovskites, along with weak n-type surface characteristics, remain critical obstacles to enhance the power conversion efficiency (PCE) of the perovskite solar cells (PSCs). Herein, an acceptor-donor-acceptor (A-D-A) type organic passivator structured with two C60 cages sandwiching a nonfullerene acceptor fragment indacenodithieno[3,2-b]thiophene (IT), namely C60-IT-C60, is designed. Morphological and spectroscopic measurements demonstrate that the S element in the IT unit and the fullerene cages of C60-IT-C60 act as a Lewis base and acid to passivate the uncoordinated Pb2+ cation and anion defects. This interaction not only aligns the energy diagram and work functions of perovskite, but also encourages the crystallization of perovskite and suppresses the deep- and shallow-level defects, leading to a maximum PCE of 24.16% (fill factor of 84.75%) with improved storage and thermal stability in the corresponding PSCs. This work provides a new design paradigm of fullerene derivatives in PSCs.

Fullerene derivatives [6], [6]-phenyl-C61-butyric acid methyl ester (PC61BM) has been routinely used as the electron transport layer (ETL) in perovskite solar cells due to its suitable energy levels and good solution processability. However, its electron mobility and conductivity still need to be further enhanced for constructing high performance perovskite solar cells (PSCs). Herein, by doping the PC61BM with a p-type polymer PM6 and n-type molecule ITIC, efficient wide-bandgap perovskite solar cells with improved efficiency and operational/storage stability are obtained. Further spectroscopy and electric measurements indicate PM6 and ITIC can both passivate defects at the perovskite/ETL interface, meanwhile ITIC can elevate the Fermi level of PC61BM to enhance conductivity and PM6 can improve the photo-induced electron mobility of the ETL, facilitating charge extraction and reducing charge recombination. As the results, Cs0.17FA0.83Pb(I0.83Br0.17)3 wide-bandgap PSCs with PM6:PC61BM:ITIC as the ETL demonstrates a superior efficiency of 22.95%, compared to 20.89% of the PC61BM assisted device.

Organic semiconductors promise highly-flexible, solution-processible electronics, and have attracted great attention in applications for photovoltaics and photodetectors. However, they also suffer from large exciton binding energy and poor charge transport ability, meaning they cannot compare with traditional inorganic alternatives. In this work, CsPbI2Br inorganic perovskite quantum dots (PQDs) were integrated into cutting-edge polymer:non-fullerene photoactive films to improve the performance of both photovoltaic (PV) and photodetecting (PD) devices. We find there is strong energy transfer from these PQDs to the donor component PM6, which results in an improved short-circuit current and photoresponsivity in PV and PD devices, whilst strong chemical interactions between PQDs and fullerene acceptor L8-BO are revealed, passivating the defects of PQDs. Mott-Schottky measurements, in conjunction with electrochemical impedance spectroscopy, further elucidate that a wider depletion region is established with the assistance of PQDs, attributed to the above interaction and larger dielectric constant enabled by PQDs, which could be the key to the accelerated charge transport and reduced charge recombination. With the integration of PQDs, an improvement in power conversion efficiency from 18.8% to 19.4% (maximum 20.2% for D18:L8-BO) is observed in PM6:L8-BO PV devices, whilst a decrease in dark current from 1.5 x 10-5 to 9.6 x 10-7 mA cm-2 at -0.1 V is obtanied in PD devices, translating to a superior detectivity of 6.5 x 1012 Jones at 770 nm.

[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) is a routinely used electron transport layer (ETL) material in perovskite solar cells (PSCs) due to its strong electron-accepting ability. However, its ball-like geometry also limits the optoelectronic property design and restricts the further efficiency elevation in PSCs. In this work, two non-fullerene acceptors (NFAs) namely BTP-C9OD and BTPV-C9OD are utilized to dope PC61BM, and we find NFAs exhibit strong interfacial orbital hybridization effect with PC61BM. This not only allows the energetics modulation of PC61BM, but also improves the conductivity and electron transport mobility of ETL. This effect is found to be more pronounced in the NFA possessing additional ethylene double bonds between the backbone and end group of NFA, attributed to the enhanced molecular planarity and extended it-electron delocalization space. These extra ethylene double bonds are found to provide stronger chemical interaction with the Pb2 + ions on the perovskite surface, suppressing the defect density and trap-assisted recombination in PSCs. Using a Cs0.17FA0.83Pb(I0.8Br0.2)3 perovskite as the active layer, the BTPV-C9OD based PSCs achieved superior open circuit voltage (VOC) of 1.281 V and a champion PCE of 24.26 %, associated with reduced non-radiative energy loss and more efficient charge extraction.

Organic photodetectors (OPDs) show promising application in environmental monitoring and wearable sensors, however, their detectivity in the near‐infrared (NIR) regime is limited. This is linked with the high energetic disorder of organic semiconductors. In this work, non‐fullerene acceptors (NFAs) with different conjugation frameworks are assembled into OPDs, and their dark current density ( J d ) and specific detectivity ( D * ) are correlated with structure. It is found that the expansion of conjugation backbone can enhance the intermolecular interactions of NFAs toward ordered molecular packing, nevertheless it also induce the formation of multi‐crystalline structure that leads to increased energetic disorder. As the results, dual‐extended NFA C5Qx‐B6F with rigid backbone and torsional end group forms a preferential face‐on molecular packing with decreased lattice mismatches, resulting in reduced energetic disorder and density of state. C5Qx‐B6F based OPD not only enables an ultra‐low J d of 4.3 × 10 −11 A cm− 2 A cm −2 at –0.1 V with remarkable specific detectivity of 6.9 × 10 13 Jones at 800 nm, but also can be utilized as the third component to suppress the energetic disorder of a near‐infrared PTB7‐Th:BTPV‐C9OD system, achieving an unprecedented D * over 10 13 Jones at 1000 nm, which is among the highest value for solution processed NIR‐OPDs.

The intermolecular interactions and aggregation behaviors of NFAs are manipulated via extending their conjugated framework, towards suppressed excitonic static disorder, fibrillar morphology and reduced energy loss in their organic photovoltaics.

Polymeric acceptors are prone to over-aggregate in photovoltaic thin films due to the entanglement of their long macromolecular chains, which hampers the exciton dissociation during the power conversion process. Although high boiling point solvent can retard the over-aggregation of polymeric acceptors, the structural order is often suppressed which will limit the charge transport in all-polymer solar cells (all-PSCs). In this work, the solvent additive 1-CN and solid additive INMB-F are combined to overcome the above issue, realizing enhanced structural order with refined phase separation in a cutting-edge PM6:PY-IT all-PSC, with a remarkable power conversion efficiency of 19.1%, which is one of the highest efficiency reported for binary PY-IT based all-PSCs. Molecular dynamics simulations and X-ray diffraction indicate that 1-CN can facilitate the disentanglement of PY-IT chains, while INMB-F can interact with these disentangled chains to promote ordered molecular stacking, thereby enhancing exciton dissociation and charge transport simultaneously. (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic) (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic) (sic)(sic)(sic)(sic)(all-PSCs)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)1-CN(sic)(sic) (sic)(sic)(sic)(sic)INMB-F(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic) (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)PM6:PY-IT(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)19.1% (sic)(sic)(sic)(sic)(sic)(sic)(sic)(PCE), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)PY-IT(sic)(sic)(sic) (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)X(sic)(sic)(sic)(sic)(sic) (sic)(sic)(sic), 1-CN(sic)(sic)(sic)(sic)PY-IT(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)INMB-F(sic)(sic)(sic)(sic)(sic) (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic) (sic)(sic)(sic)(sic)(sic)(sic).

Polymeric semiconducting materials struggle to achieve fast charge mobility due to low structural order. In this work, five 1H-indene-1,3(2H)dione-benzene structured halogenated solid additives namely INB-5F, INB-3F, INB-1F, INB-1Cl, and INB-1Br with gradually varied electrostatic potential are designed and utilized to regulate the structural order of polymer donor PM6. Molecular dynamics simulations demonstrate that although the dione unit of these additives tends to adsorb on the backbone of PM6, the reduced electrostatic potential of the halogen-substituted benzene can shift the benzene interacting site from alkyl side chains to the conjugated backbone of PM6, not only leading to enhanced π-π stacking in out-of-plane but also arising new π-π stacking in in-plane together with the appearance of multiple backbone stacking in out-of-plane, consequent to the co-existence of face-on and edge-on molecular orientations. This molecular packing transformation further translates to enhanced charge transport and suppressed carrier recombination in their photovoltaics, with a maximum power conversion efficiency of 19.4% received in PM6/L8-BO layer-by-layer deposited organic solar cells.

The bandgap tunability of halide perovskites makes perovskite solar cells excellent building blocks for multijunction architectures that can overcome the fundamental efficiency limits of single-junction devices. Meanwhile, the introduction of non-fullerene acceptors has led to tremendous advances in the field of organic solar cells. Organic and perovskite semiconductors share similar processing technologies, making them attractive partners for multijunction architectures. This Perspective article outlines the prospects and challenges of perovskite–organic tandem solar cells by highlighting the key aspects of the individual building blocks and how they interact with one another. The discussion includes the role of non-fullerene acceptors in narrow-gap organic solar cells with high operational stability, the need for long-term stability in wide-gap perovskite solar cells and the impact of the design and functionality of high-quality interconnects on the characteristics of the tandem device. Finally, the prospects of perovskite–organic tandem solar cells are benchmarked against other emerging tandem solar cell technologies.

All polymer solar cells (all-PSCs) promise mechanically-flexible and morphologically-stable organic photovoltaics and have aroused increased interests very recently. However, due to their disorderly conformation structures within the photoactive film, inefficient charge generation and carrier transport are observed which lead to inferior photovoltaic performance compared to smaller molecular acceptor-based photovoltaics. Here, by diluting PM6 with a cutting-edge polymeric acceptor PY-IT and diluting PY-IT with PM6 or D18, donor-dominating or acceptor-dominating heterojunctions were prepared. Synchrotron X-ray and multiple spectrometer techniques reveal that the diluted heterojunctions receive increased structural order, translating to enhanced carrier mobility, improved exciton diffusion length, and suppressed non-radiative recombination loss during the power conversion. As the results, the corresponding PM6+1%PY-IT/PY-IT+1%D18 and PM6+1%PY-IT/PY-IT+1%PM6 devices fabricated by layer-by-layer deposition received superior power conversion efficiency (PCE) of 19.4% and 18.8% respectively, along with enhanced operational lifetimes in air, outperforming the PCE of 17.5% in the PM6/PY-IT reference device.

Organic photovoltaics (OPVs) suffer from a trade-off between efficient charge transport and suppressed nonradiative recombination due to the aggregation-induced luminance quenching of organic semiconductors. To resolve this grand challenge, a pi-extended nonfullerene acceptor (NFA) B6Cl with large voids among the honeycomb network is designed and introduced into photovoltaic systems. We find that the presence of a small amount of (i.e., 0.5 or 1 wt %) B6Cl can compress the molecular packing of the host acceptor L8-BO, leading to shortened pi-pi stacking distance from 3.59 to 3.50 & Aring; (that will improve charge transport) together with ordered alkyl chain packing (that will inhibit nonradiative energy loss due to the suppressed C-C and C-H bonds vibrations), as validated by high-energy X-ray scattering measurements. This morphology transformation ultimately results in simultaneously improved J(SC), FF, and V-OC of OPVs(.) As a result, the maximum PCEs of PM6:L8-BO and D18:L8-BO are increased from 19.1 and 19.3% to 19.8 and 20.2%, respectively, which are among the highest values for single-junction OPVs. The university of B6Cl to increase the performance of OPVs is further evidenced in a range of polymer:NFA OPVs.

UV-light illumination converts the aromatic conformation of polymer donors into a rigid quinone structure, resulting in compact fibrillar aggregation of the active layer to achieve a maximum efficiency of 19.9% of single-junction organic solar cells.

The nanoscale fibrillar morphology, featuring long-range structural order, provides abundant interfaces for efficient exciton dissociation and high-quality pathways for effective charge transport, is a promising morphology for high performance organic solar cells. Here, we synthesize a thiophene terminated non-fullerene acceptor, L8-ThCl, to induce the fibrillization of both polymer donor and host acceptor, that surpasses the 20% efficiency milestone of organic solar cells. After adding L8-ThCl, the original weak and less continuous nanofibrils of polymer donors, i.e. PM6 or D18, are well enlarged and refined, whilst the host acceptor L8-BO also assembles into nanofibrils with enhanced structural order. By adapting the layer-by-layer deposition method, the enhanced structural order can be retained to significantly boost the power conversion efficiency, with specific values of 19.4% and 20.1% for the PM6:L8-ThCl/L8-BO:L8-ThCl and D18:L8-ThCl/L8-BO:L8-ThCl devices, with the latter being certified 20.0%, which is the highest certified efficiency reported so far for single-junction organic solar cells. The nanoscale fibrillar morphology of the photoactive layer is critical to improve performance of organic solar cells. Here, the authors incorporate thiophene terminal groups in the non-fullerene acceptor, realizing nanofibrils with enhanced structural order and certified device efficiency of 20%.

Constructing fibril morphology has been believed to be an effective method of achieving efficient exciton dissociation and charge transport in organic solar cells (OSCs). Despite emerging endeavors on the fibrillization of organic semiconductors via chemical structural design or physical manipulation, tuning of the fibril geometry, i.e., width and length, for tailored optoelectronic properties remains to be studied in depth. In this work, a series of alkoxythiophene additives featuring varied alkyl side chains connected to thiophene are designed to modulate the growth of fibril aggregates in cutting-edge polymer donors PM6 and D18. Molecular dynamics simulations and morphological characterizations reveal that these additives preferentially locate near and entangle with the side chains of polymer donors, which enhance the conjugated backbone stacking of polymer donors to form nanofibrils with the width expanding from 12.6 to 21.8 nm and the length increasing from 98.3 to 232.7 nm. This nanofibril structure is feasible to acquire efficient exciton dissociation and charge transport simultaneously. By integrating the fibril PM6 and L8-BO as the donor and acceptor layers in pseudo-bulk heterojunction (p-BHJ) OSCs via layer-by-layer deposition, an improvement of power conversion efficiency (PCE) from 18.7% to 19.8% is observed, contributed by enhanced light absorption, charge transport, and reduced charge recombination. The versatility of these additives is also verified in D18:L8-BO OSCs, with enhanced PCE from 19.3% to 20.1%, which is among the highest values reported for OSCs.

Organic semiconductors usually exhibit low structural-order owing to their weak intermolecular interactions, which leads to inferior charge transport and strong carrier recombination in photovoltaics. In this work, three thiophene structured solid additives namely thieno[3,2-b]thiophene (TT), 3,6-dibromothieno[3,2-b]thiophene (TTBB) and 3-bromo-6-iodio-thieno[3,2-b]thiophene (TTBI) are utilized to enhance the molecular interactions in a range of electron donors and acceptors. X-ray technique and molecular dynamics simulations reveal that by adjusting their electrostatic potential and dipole moment, their interacting site and interaction energy with donor (PM6 and D18) or acceptor (L8-BO) can be finely tuned. We find the most electropositive TTBB shows the strongest interaction with PM6, leading to enhanced crystallization; whilst the asymmetric TTBI brings the strongest molecular packing of L8-BO, consequent to more compact pi-pi stacking and ordered alkyl chain packing. As the results, the bulk heterojunction PM6:L8-BO photovoltaics upon the assistance of TTBI or TTBB obtain improved charge transport and reduced non-radiative energy loss, translating to power conversion efficiency (PCE) values of 18.7 % and 19.1 %. When further taking the synergetic effect of TTBB and TTBI on PM6(D18) and L8-BO respectively, the layer-by-layer deposited PM6(TTBB)/L8-BO(TTBI) and D18(TTBB)/L8-BO(TTBI) allowed superior PCEs of 19.4 % and 19.9 %, which are among the highest values of single-junction organic solar cells.

The photoactive layer of organic solar cells consists of p-type electron donors and n-type electron acceptors, which phase separate to form fine and continuous networks for charge transport. The impact of the donor–acceptor interaction on the microstructure and optoelectronics of the photoactive layer remains unclear. In this work, a tiny amount (1 wt%) of donor PM6 is added into the non-fullerene acceptor (NFA) C8- R or L8-BO (or vice versa) to form a donor (or acceptor) diluted heterojunction. The structural order is improved through dipole–dipole interaction between the donor and the acceptor owing to their opposite electronegativity. We fabricate a pseudo-bilayer heterojunction solar cell based on NFA-diluted donor (that is, donor + 1% NFA) and donor-diluted NFA (that is, NFA + 1% donor) layers: the device exhibits superior power conversion efficiencies compared with their bulk heterojunction and conventional pseudo-bilayer counterparts. We demonstrate an efficiency of 19.4% (certified 19.1%) and 17.6% for 100 and 300 nm-thick PM6 + 1% L8-BO/L8-BO + 1% PM6 solar cells, respectively.