Exciton Dissociation Research Articles

The Influence of Electrochemical Bias on the Exciton Dynamics of MoS2 thin Films

2D transition metal dichalcogenides are an attractive family of materials in the field of electronics and optoelectronics. They are excellent candidates for sensitive photodetectors, light harvesting devices (photovoltaics, photocatalysts or photoelectrodes), lasers or non-linear optical devices. All these applications rely on light-matter interactions, which processes will ultimately decide the efficiency of the derived devices. Understanding carrier dynamics and the interaction of various exotic quasi-particles (excitons, trions) in these materials is of paramount importance to design better performing devices.Pump-probe transient absorption/reflection spectroscopy (TAS/TRS) is a powerful technique to study photophysical processes involved in charge carrier generation and recombination on the ultrafast timescale. In MoS2 photoelectrodes after light excitation different types of excitons are generated, and their decay can be monitored with these techniques. Coupling electrochemical techniques with these ultrafast methods, allows to probe the decay of the excited state in these materials under working conditions. In this manner the effect of trap state filling [1] or the effect of charge extraction [2] on the charge carrier dynamics of photoelectrochemical systems can be revealed.In my presentation I will show ultrafast spectroelectrochemical measurements on ITO/MoS2 photoelectrodes and reveal how the decay of excitons are influenced by the applied electrochemical bias. By comparing results from TAS/TRS spectroscopy the separation of carrier dynamics on the surface and bulk of these systems can be performed. These measurements reveal that the dissociation of excitons occurs at the ITO/MoS2 interface, resulting in a long living exciton population on the surface of these samples. Charging/discharging studies carried out in these systems reveal that the trap states involved in the dissociation of excitons in these systems can be permanently filled. The electrochemical filling of these trap states allows the tuning of the excited state lifetime of these systems, which can aid the better design of photoelectrochemical devices based on MoS2.

Theoretical Study on Functionalizing A–D–A Type Non‐Fullerene Acceptor by Fused Rings and Side Chains for Organic Solar Cells

AbstractThe modification of fused rings in the central backbone, side chains, and end groups of the non‐fullerene acceptor (NFA) for organic solar cells (OSCs) can modulate properties and photovoltaic performance. In order to investigate the effect of fused rings and side chains on photovoltaic performance, PBDB‐T is selected as electron donor and IDTIC, IDIC, IDIC‐PhC6, IDIC‐C4Ph, 4TIC, ITIC‐OE, IDTTIC, ITC6‐IC, ITIC, and C8‐ITIC are selected as NFAs. Based on quantum chemistry calculations, the geometries, electronic structures, excitation properties, excited‐state lifetimes, and electrostatic potentials (ESPs) of the monomer and the PBDB‐T:NFA complexes are studied, and the rate constants of charge transfer (CT), exciton dissociation (ED) and charge recombination (CR) processes are analyzed. The results show that the increase of fused‐ring in NFA's backbone by substituting phenyl or thienyl with bithiophene can elevate the highest occupied molecular orbital energies, reduce the gap of frontier molecular orbital energies, induce red‐shift of absorption spectrum, increase CT energy, improve CT and ED rates. This work provides a detailed understanding of tuning optoelectronic properties and photovoltaic performance by modifying NFA's side chains and extending backbones.

Solid Additive‐Assisted Selective Optimization Strategy for Sequential Deposited Active Layers to Construct 19.16% Efficiency Binary Organic Solar Cells

AbstractVolatile solid (VS)‐additives are regarded as an effective tool to manipulate morphology of sequential deposited (SD) active layers for improving power conversion efficiencies (PCEs) of organic solar cells (OSCs), while the independent effect of VS‐additives on donor and acceptor layers is often overlooked. Herein, a new VS‐additive named 2‐(2‐methoxyphenyl)benzo[b]thiophene (BTO) is synthesized and applied in SD binary PM6/L8‐BO active layers. Introducing it into bottom PM6 layer (PM6+), BTO has a low volatility and longer volatilization distance, which prolongs the interaction time between BTO and L8‐BO in PM6+/L8‐BO film, leading to an over‐aggregated L8‐BO. While inserting it into top L8‐BO layer (L8‐BO+), the fast evaporation of BTO and excellent dipole interaction between BTO and L8‐BO help to enhance molecular absorption, crystallinity, and ordered packing of PM6/L8‐BO+ system. Therefore, an optimized morphology with proper phase separation is achieved to increase exciton dissociation and charge transfer properties, restrain charge recombination and energy loss of OSCs, yielding an impressive PCE of over 19%. Furtherly, using D18 instead of PM6, binary SD‐systems offer a record‐high PCE of 19.16%. The developed selective optimization strategy for SD active layers provides a deep insight into the working mechanism of VS‐additives for boosting PCE of OSCs.

Photoenzymatic CO2 Reduction Dominated by Collaborative Matching of Linkage and Linker in Covalent Organic Frameworks.

Artificial photoenzymatic systems based on covalent organic frameworks (COFs) provide an interesting platform for converting CO2 to value-added fuels. However, the dual roles of COFs as photocatalysts and enzyme hosts showcase contradictory preferences for structures, which poses a great challenge for their rational design. Herein, we report the collaborative matching of linkages and linkers in COFs on their ability to exert both photocatalytic activity and enzyme loading, which has been neglected until now. The linkage-dependent linker regulation pattern was elucidated, and the optimal match showed a record-breaking apparent quantum efficiency at 420 nm for photocatalytic cofactor regeneration of 13.95% with a high turnover frequency of 5.3 mmol g-1 h-1, outperforming other reported crystalline framework photocatalysts. Moreover, theoretical calculations and experiments revealed the mechanism underlying the effects of matching the linkage and linker on exciton dissociation and charge migration in photocatalysis. This newfound understanding enabled the construction of COFs with both high photoactivity and large pores closer in size to the formate dehydrogenase, achieving high loading capacity and a suitable confinement effect. Remarkably, the artificial photoenzymatic system constructed according to optimal linkage-linker matching exhibited highly efficient CO2 reduction, yielding formic acid with a specific activity as high as 1.46 mmol g-1 catalyst h-1 and good reusability, paving the way for sustainable CO2 conversion driven by visible light.

Semitransparent Organic Photovoltaics Utilizing Intrinsic Charge Generation in Non-Fullerene Acceptors.

In organic semiconductors, a donor/acceptor heterojunction is typically required for efficient dissociation of excitons. Using transient absorption spectroscopy to study the dynamics of excited states in non-fullerene acceptors (NFAs), it is shown that NFAs can generate charges without a donor/acceptor interface. This is due to the fact that dielectric solvation provides a driving force sufficient to dissociate the excited state and form the charge-transfer (CT) state. The CT state is further dissociated into free charges at interfaces between polycrystalline regions in neat NFAs. For IEICO-4F, incorporating just 9 wt% donor polymer PTB7-Th in neat films greatly boosts charge generation, enhancing efficient exciton separation into free charges. This property is utilized to fabricate donor-dilute organic photovoltaics (OPV) delivering a power conversion efficiency of 8.3% in the case of opaque devices with a metal top-electrode and an active layer average visible transmittance (AVT) of 75%. It is shown that the intrinsic charge generation in low-bandgap NFAs contributes to the overall photocurrent generation. IEICO-4F-based OPVs with limited PTB7-Th content have high thermal resilience demonstrating little drop in performance over 700h. PTB7-Th:IEICO-4F semitransparent OPVs are leveraged to fabricate an 8-series connected semitransparent module, demonstrating light-utilization efficiency of 2.2% alongside an AVT of 63%.

Asymmetric Π-Bridge Engineering Enables High-Permittivity Benzo[1,2-B:4,5-b']Difuran-Conjugated Polymer for Efficient Organic Solar Cells.

Organic solar cells (OSCs) exhibit complex charge dynamics, which are closely correlated with the dielectric constant (ɛr ) of photovoltaic materials. In this work, a series of novel conjugated copolymers based on benzo[1,2-b:4,5-b']difuran (BDF) and benzotriazole (BTz) is designed and synthesized, which differ by the nature of π-bridge from one another. The PBDF-TF-BTz with asymmetric furan and thiophene π-bridge demonstrates a larger ɛr of 4.22 than PBDF-dT-BTz with symmetric thiophene π-bridge (3.15) and PBDF-dF-BTz with symmetric furan π-bridge (3.90). The PBDF-TF-BTz also offers more favorable molecular packing and appropriate miscibility with non-fullerene acceptor Y6 than its counterparts. The corresponding PBDF-TF-BTz:Y6 OSCs display efficient exciton dissociation, fast charge transport and collection, and reduced charge recombination, eventually leading to a power conversion efficiency of 17.01%. When introducing a fullerene derivative (PCBO-12) as a third component, the PBDF-TF-BTz:Y6:PCBO-12 OSCs yield a remarkable FF of 80.11% with a high efficiency of 18.10%, the highest value among all reported BDF-polymer-based OSCs. This work provides an effective approach to developing high-permittivity photovoltaic materials, showcasing PBDF-TF-BTz as a promising polymer donor for constructing high-performance OSCs.

Highly-Efficient 2D Nonfullerene Acceptors Enabled by Subtle Molecular Tailoring Engineering.

The conjugate expansion of nonfullerene acceptors is considered to be a promising approach for improving organic photovoltaic performance because of its function in tuning morphological structure and molecular stacking behavior. In this work, two nonfullerene acceptors are designed and synthesized using a 2D π-conjugate expansion strategy, thus enabling the construction of highly-efficient organic solar cells (OSCs). Compared with YB2B (incorporating dibromophenanthrene on the quinoxaline-fused core), YB2T (incorporating dibromobenzodithiophene on the quinoxaline-fused core) has red-shifted spectral absorption and better charge transport properties. Moreover, the more orderly and tightly intermolecular stacking of YB2T provides the possibility of forming a more suitable phase separation morphology in blend films. Through characterization and analysis, the YB2T-based blend film is found to have higher exciton dissociation efficiency and less charge recombination. Consequently, the power conversion efficiency (PCE) of 17.05% is achieved in YB2T-based binary OSCs, while YB2B-based devices only reached 10.94%. This study demonstrates the significance of the aromatic-ring substitution strategy for regulating the electronic structure and aggregation behavior of 2D nonfullerene acceptors, facilitating the development of devices with superior photovoltaic performance.

Revealing the Effect of Halogenation Strategy on the Regulation of Crystallization Kinetics and Molecular Packing for High‐Performance Organic Solar Cells

AbstractHalogenation of non‐fused ring electron acceptors (NFREAs) plays an important role in regulating their optoelectronic properties. However, the underlying mechanisms and their impact on the performance of organic solar cells (OSCs) have remained unclear. Herein, a series of halogenated NFREAs incorporating F, Cl, and Br, are prepared to study their effect on crystallization kinetics, phase separation, molecular packing, and charge transport. Among various halogenation strategies, chlorination minimizes the Coulomb attractive energy between donor and acceptor, thereby facilitating exciton dissociation. In situ UV–vis absorption tests reveal that chlorinated acceptors exhibit a longer crystallization time, effectively suppressing excessive molecular aggregation and enhancing overall crystallinity. Additionally, chlorinated acceptors exhibit a longer exciton diffusion length, which promotes exciton dissociation while mitigating charge recombination in the devices. Consequently, two chlorinated NFREAs, TCN‐Cl, and PCN‐Cl, yield an impressive power conversion efficiency (PCE) of 14.85% and 15.30%, respectively, when blended with PM6 and J52 donors. These values represent the highest reported PCEs to date for NFREAs with A‐π‐A’‐π‐A and A‐π‐D‐π‐A structures. The study elucidates the crucial role of chlorination in extending exciton diffusion length and crystallization time. These effects significantly benefit phase separation within the active layers, enhance charge separation, and suppress recombination for achieving high‐efficiency OSCs.

High‐Performance Near‐Infrared Organic Photodetectors Enabled by Fabricating an Interdigital Heterojunction

AbstractNear‐infrared organic photodetectors (NIR‐OPDs) are of significant applications in optical communication, medical monitoring, and bioimaging, and have become a centerpiece of organic photodetector (OPD) research. To overcome the well‐known challenge of high dark current in NIR‐OPDs, researchers have investigated and introduced the sequential deposition method to prepare photosensitive layers of gradient heterojunction structure. However, this photosensitive layer suffers from the issue of insufficient exciton diffusion length, which in turn limits the photoresponse performance of devices. To address this issue, an interdigital heterojunction (IHJ) structure is designed, forming the adjustable large‐area bicontinuous phase, and constructing rich donor/acceptor interfaces and straightforward carrier transport channels. In this structure, the film shows enhanced crystallinity, which effectively reduces the trap density and suppresses the dark current. In addition, efficient exciton dissociation and charge extraction along with suppressed charge complexation promote the enhanced photoresponse of IHJ devices. Consequently, the IHJ NIR‐OPD achieves a high detectivity of 7.35 × 1013 Jones at 805 nm at −0.2 V, which is one of the highest values at 800–900 nm among reported NIR‐OPDs. Further, the IHJ devices are successfully applied to arterial pulse monitoring and transmission‐based bioimaging. This study provides new insights for realizing high‐performance NIP‐OPDs.

Crystal structures and photoluminescence characteristics of cesium lead bromide perovskite nanoplatelets depending on the antisolvent and ligand used in their syntheses

Cesium lead bromide (CsPbBr3) nanocrystals (NCs) with nanoplatelet shapes and different crystal structures were synthesized via the ligand-assisted reprecipitation (LARP) method using different pairs of ligands and antisolvents, namely oleic acid (OA) or linoleic acid (LA) as the ligand and toluene or chloroform as the antisolvent. The XRD data revealed that the obtained CsPbBr3 NCs have different crystal structures, namely orthorhombic, tetragonal, and cubic, depending on the ligand and antisolvent pair, which exhibited significantly different photoluminescence (PL) characteristics. From the XPS data, these CsPbBr3 nanoplatelets showed two doublet peaks of the Br-3d orbital at different binding energies, representing two different chemical environments of the Br bonds. The doublet peak apparent at a higher binding energy was associated with the Br chemical states at the crystal surface, which appeared because of the distorted crystal structure resulting from the interaction of the solvent and ligand with Br ions. The PL emission consists of three luminescence centers: a PL band peaked at 520 nm (A band), a PL band peaked at 540 nm (B band), and a PL band tail, which can be discussed in terms of exciton models. Stable and intense luminescence was observed in CsPbBr3 nanoplatelets synthesized using a pair of toluene antisolvent and LA ligand, namely CsPbBr3#(Tl/LA). The orthorhombic crystal structure and distorted crystal surface in this sample may lead to confinement of the photogenerated small exciton-polaron and weak phonon interactions, which effectively hinder exciton dissociation, particularly at the crystal surface, resulting in intense PL. The results of this study may provide additional important insights into the role of the antisolvent and ligand in the formation of CsPbBr3 NCs and the exciton behavior in their PL characteristics, which may also be found in other types of halide perovskites.

Low bandgap fused-ring electron acceptors based on π-expended asymmetric benzotrithiophene core: Regulating aggregation and photovoltaic performance by side chain isomerization

Asymmetric molecular design strategy has received increasing attention in the development of fused-ring electron acceptors (FREAs). Benzo [2,1-b: 3,4-b’: 5,6-b”] trithiophene (asym-BTT) with intrinsically asymmetric and electron-rich π-plane is an ideal unit to construct asymmetric FREAs, whereas asym-BTT-based FREAs are still very limited. Herein, two asymmetric FREAs based on the π-expended asym-BTT fused-core with para-hexylphenyl and meta-hexylphenyl side chains (p-FABTT and m-FABTT) have been developed. Owing to strong electron-donating ability and planar configuration of π-expended asym-BTT fused-core, two acceptors exhibit effective intramolecular charge transfer and intermolecular interaction, leading to near infrared absorption above 900 nm with narrow bandgaps of around 1.34 eV. Although the same π-conjugated backbones of two acceptors afford the nearly identical energy levels and solution absorptions, side chain isomerization leads to significant differences in film absorption, molecular stacking orientation and crystallinity. In neat film, the m-FABTT with meta-hexylphenyl side chains exhibits slightly redshifted absorption with stronger 0-0 absorption peak from J-aggregation compared to p-FABTT with para-hexylphenyl side chains. More orderly molecular stacking and stronger π-π interactions with shorter π-π stacking distance in both the neat film and active layer can be observed for m-FABTT. When blended with donor polymer D18, m-FABTT exhibits broadened spectral region and proper phase separation morphology for effective exciton dissociation and charge transport. Therefore, the OSCs device based on m-FABTT achieves an optimal PCE of 7.14 % with a higher JSC of 15.39 mA cm−2 and an improved FF of 57.96 % as comparing with p-FABTT-based device (a PCE of 4.81 % with a JSC of 11.67 mA cm−2 and a FF of 48.51 %).

Manipulating Vertical Phase Separation Enables Pseudoplanar Heterojunction Organic Solar Cells Over 19% Efficiency via Ternary Polymerization.

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.

Single-atomic Co-N site modulated exciton dissociation and charge transfer on covalent organic frameworks for efficient antibiotics degradation via peroxymonosulfate activation

Covalent organic framework (COF) materials have received extensive attention in the field of photocatalysis in recent years, but the strong exciton effect in COF has seriously affected the separation of electron-hole pairs so that limiting the enhancement of the photocatalytic performance. It is of great significance to explore suitable ways to regulate the exciton behavior in COF materials and enhance their electron-hole's separation efficiency. By anchoring Co single-atoms within a silver birch leaf-like COF framework (COF-Cox), the exciton in COF is effectively dissociated by forming Co-N sites, producing massive free electrons and holes. Co-N sites also facilitate photogenerated holes aggregation toward Co single-atoms, which effectively drives the carriers' separation in COF framework. The carrier concentration of COF-Co10 is 2.81 times higher compared with the original COF. The reduced exciton binding energy (Eb) further proves that the the formation of Co-N sites promote the exciton dissociation. Consequently, COF-Cox can well activate peroxymonosulfate (PMS) to degrade tetracycline (TC) pollutants, the reaction rate constant of COF-Co10 (3.65 × 10-2 min−1) is 5.27 times higher than COF (6.93 × 10-3 min−1). The possible activation routes and degradation products of TC are also discussed. This study provides a more comprehensive understanding of the exciton behavior for the design of more efficient COF-based catalysts.

Oxygen vacancy in CoO/reduced graphene oxide composite for enhancing long-term effectiveness of photocatalytic CO2 reduction via mediating exciton

Photocatalytic reduction of carbon dioxide (CO2) has been expected to be an effective way to reduce carbon emissions. Designing photocatalytic materials with long-term effectiveness is the key of photocatalytic technology. In this work, CoO nanoparticles loaded on the surface of reduced graphene oxide (rGO) membranes on silicon substrate were in-situ fabricated by one-step method. The resulting materials can convert CO2 into carbon monoxide (CO) up to 70 h at a steady rate of ∼185 ± 30 µmol g−1 h−1 with a selectivity of nearly 100%. This material system contained rich oxygen vacancies and generated new oxygen vacancies during the photocatalytic process. Oxygen vacancies mediate the interactions with excitons: (i) promoting the dissociation of free excitons; (ii) leading to form bound excitons under the coupling effect with phonons, inhibiting the recombination of photogenerated electrons and holes as well as enhancing the long-term effectiveness of photocatalytic CO2 reduction. We hope this work can provide valuable insights for the design and optimization of photocatalytic materials.

18.6% Efficiency All-Polymer Solar Cells Enabled by a Wide Bandgap Polymer Donor Based on Benzo[1,2-d:4,5-d']bisthiazole.

The limited selection of wide bandgap polymer donors for all-polymer solar cells (all-PSCs) is a bottleneck problem restricting their further development and remains poorly studied. Herein, a new wide bandgap polymer, namely PBBTz-Cl, is designed and synthesized by bridging the benzobisthiazole acceptor block and chlorinated benzodithiophene donor block with thiophene units for application as an electron donor in all-PSCs. PBBTz-Cl not only possesses wide bandgap and deep energy levels but also displays strong absorption, high-planar structure, and good crystallinity, making it a promising candidate for application as a polymer donor in organic solar cells. When paired with the narrow bandgap polymer acceptor PY-IT, a fibril-like morphology forms, which facilitates exciton dissociation and charge transport, contributing to a power conversion efficiency (PCE) of 17.15% of the corresponding all-PSCs. Moreover, when introducing another crystalline polymer acceptor BTP-2T2F into the PBBTz-Cl:PY-IT host blend, the absorption ditch in the range of 600-750nm is filled, and the blend morphology is further optimized with the trap density reducing. As a result, the ternary blend all-PSCs achieve a significantly improved PCE of 18.60%, which is among the highest values for all-PSCs to date.

A TiO2-based hybrid solar cell device fabricated by employing interfacial modification and morphology control strategies

Heterojunction interface properties are important in organic-inorganic hybrid solar cells. To improve the cell performance, it was regulated by introducing two triphenylamine-based modifiers and adjusting the morphology of TiO2. It showed that these strategies are beneficial to improving the chemical compatibility between inorganic and organic materials, inhibiting charge recombination and accelerating excitons dissociation efficiency. The power conversion efficiency of the device was improved from 0.17 % to 2.10 %. It was further optimized to 4.90 % by adjusting the morphology of TiO2 nanorods. The interfacial charge transfer/recombination dynamic mechanisms and the intrinsic factors were analyzed in detail by diverse electrochemical measurements.

Achieving Desired Pseudo-Planar Heterojunction Organic Solar Cells via Binary-Dilution Strategy.

The sequential deposition process has demonstrated the great possibility to achieve a photolayer architecture with an ideal gradient phase separation morphology, which has a vital influence on the physical processes that determine the performance of organic solar cells (OSCs). However, the controllable preparation of pseudo-planar heterojunction (P-PHJ) with gradient distribution has not been effectively elucidated. Herein, a binary-dilution strategy is proposed, the PM6 solution with micro acceptor BO-4Cl and the L8-BO solution with micro donor PM6 respectively, to form P-PHJ film. This architecture exists good donor (D) and acceptor (A) vertical gradient distribution and larger D/A interpenetrating regions, which promotes exciton generation and dissociation, shortens charge transport distance and optimizes carrier dynamics. Moreover, the dilution of PM6 by BO-4Cl promotes the regulation of active layer aggregation size and phase purity, thus alleviating energy disorder and voltage loss. As a result, the P-PHJ device exhibits an outstanding power conversion efficiency of 19.32% with an excellent short-circuit current density of 26.92mA cm-2 , much higher than planar binary heterojunction (17.67%) and ternary bulk heterojunction (18.49%) devices. This research proves a simple but effective method to provide an avenue for constructing desirable active layer morphology and high-performance OSCs.

Precise synthesis and photovoltaic properties of giant molecule acceptors

Series of giant molecule acceptors DY, TY and QY with two, three and four small molecule acceptor subunits are synthesized by a stepwise synthetic method and used for systematically investigating the influence of subunit numbers on the structure-property relationship from small molecule acceptor YDT to giant molecule acceptors and to polymerized small molecule acceptor PY-IT. Among these acceptors-based devices, the TY-based film shows proper donor/acceptor phase separation, higher charge transfer state yield and longer charge transfer state lifetime. Combining with the highest electron mobility, more efficient exciton dissociation and lower charge carrier recombination properties, the TY-based device exhibits the highest power conversion efficiency of 16.32%. These results indicate that the subunit number in these acceptors has significant influence on their photovoltaic properties. This stepwise synthetic method of giant molecule acceptors will be beneficial to diversify their structures and promote their applications in high-efficiency and stable organic solar cells.

A review on smart strategies for active layer phase separation regulation of organic solar cells

Exciton dissociation and charge transport are important processes in the photoelectric conversion of organic solar cells (OSCs), directly affecting the performance of OSCs. In order to facilitate exciton dissociation, phase separation size should be as small as possible. However, for the sake of continuous charge transport, a large phase separation size is also necessary. To balance these two conflicting needs, it is of utmost importance to regulate the phase separation of the active layer. This Review mainly elaborated the smart tactics commonly adopted to phase separation optimization, aiming to understand how these treatments affect both the active layer phase separation and the performance of OSCs. Furthermore, we present an outlook on the new opportunities of phase separation regulation of the active layer. Finally, this Review may provide some reference for the researchers engaged in the research of OSCs.

Empirical Model of the Charge Carriers’ Photogeneration in Organic Solar Cells

A model of the photocurrent generation of charge carriers in blends of donor (D) and acceptor (A)materials structured on the nanoscale is considered. The absorption of a quantum of light in one of thesematerials creates a molecular exciton, which can reach the interface between the D and A phases and form aninterfacial charge transfer (CT) exciton on this interface, which dissociates into an electron-hole pair. Theprobabilities of the dissociation of CT excitons into free current carriers are calculated as a function of theelectric field and the thermalization length of the electron-hole pair.