Planar Heterojunction Devices Research Articles

Bulk Heterojunction Antimony Selenosulfide Thin‐Film Solar Cells with Efficient Charge Extraction and Suppressed Recombination

AbstractAs an emerging earth‐abundant light harvesting material, antimony selenosulfide (Sb2(S,Se)3) has received tremendous attention for photovoltaics. Manipulating the carrier separation and recombination processes is critical to achieve high device efficiency. Compared to the conventional planar heterojunction (PHJ), the bulk heterojunction (BHJ) configuration affords great potential to enable efficient charge extraction. In this work, BHJ Sb2(S,Se)3 solar cells are constructed based on CdS nanorod arrays (NRAs). Highly ordered CdS NRAs with appropriate nanorod lengths and diameters are obtained by regulating the growth environment and screening different substrates for CdS deposition. A low‐temperature oxygen doping strategy implemented on CdS NRAs is further developed to improve the optoelectronic and defect properties as well as form a favorable cascade band structure for CdS NRAs, so as to realize more efficient charge extraction and suppressed recombination at the heterointerface. As a result, the CdS NRAs‐based superstrated BHJ Sb2(S,Se)3 solar cell yields a considerable power conversion efficiency of 8.04%, outperforming that of the PHJ device. A careful comparative study of PHJ and BHJ based on electrostatic field simulations indicates that the BHJ allows more efficient charge extraction and transport. This work highlights the great potential of BHJ configuration for constructing high‐performance antimony chalcogenide solar cells.

P-n Homojunction perovskite solar cells: effects of ionic density and thickness of the doped layers

The p-n homojunction perovskite solar cells are promising in comparison to planar heterojunction perovskite solar cells. It is observed that the p-n homojunction provides an efficient built-in electric field for the photo-generated electron-hole pairs to dissociate into free charge-carriers and orient them to transport to the respective electrodes, thereby reducing the overall losses due to recombination processes. However, the existence of p-n homojunction, while in operation, is currently undergoing experimental tests. In this study, we simulated the current-voltage characteristics of both planar heterojunction and p-n homojunction perovskite solar cells. For simulation, we utilised a one-dimensional drift-diffusion equation. The current-voltage characteristics show a high fill factor for the p-n homojunction devices indicating better power conversion efficiency as compared to that of planar heterojunction devices. In addition, we report the spatial distribution of electron- and hole-density with variations in (i) the mobile ionic density, inherently present in the perovskite material and (ii) the thickness of p- and n-type perovskite layers. It is observed that the role of p-n homojunction ceases when the ionic density is higher than 1017 cm−3 or when one of the doped layers is substantially thicker as compared to the other. We correlate the cease of p-n homojunction to (i) the ionic effect which screens the built-in field, and (ii) the predominance of the effect of one doped layer over the other. The study provides impetus to the development of the p-n homojunction perovskite solar cells.

Spontaneously spreading film process to improve the photovoltaic performance of organic solar cells with PHJ structure.

Efficient charge transport and extraction within the active layer plays a major role in the photovoltaic performance of organic solar cells (OSCs). In this work, the spontaneously spreading (SS) process was utilized to achieve sequential deposition of the active layer with a planar heterojunction (PHJ) structure. The SS process avoids the damage of the upper layer solution to the lower layer film by the spin coating process. The film with PHJ structure exhibits notable vertical phase separation compared to the bulk heterojunction (BHJ). Moreover, the power conversion efficiency (PCE) of the PHJ device (12.00%) is significantly higher than that of the BHJ (10.84%) due to the efficient charge transport. This work offers a novel fabrication method and device structure to enhance the photovoltaic performance of OSCs.

Panchromatic photomultiplication-type organic photodetectors with planar/bulk heterojunction structure

Broadband organic photodetectors (OPDs) can be integrated into various wearable devices and show great application potential in health monitoring and other fields. Here, we demonstrated high-performance broadband photomultiplication-type OPDs (PM-OPDs) based on MoO3 trapping electron-assisted hole tunneling injection mechanism with small-molecule lead (II) phthalocyanine (PbPc) and C70 fullerene as the donor and acceptor, respectively. In order to control the crystal phase structure formed by PbPc molecules, we prepared PbPc:C70 bulk heterojunction (BHJ) and PbPc/C70 planar heterojunction (PHJ) devices. It can be seen that the PHJ device exhibits stronger near-infrared (NIR) absorption characteristics, which is more conducive to the formation of the triclinic phase structure of the PbPc molecule. We further prepared flat panchromatic PM-OPDs in the range of 300–1000 nm by using materials (PbPc and SubPc) with absorption complementary characteristic as the active layers and PHJ/BHJ hybrid heterojunction structure. The external quantum efficiency of the resulting panchromatic PM-OPDs exceeds 1000% in the whole spectral response range under −8 V reverse bias. Finally, we prepared flexible panchromatic PM-OPDs on polyethylene terephthalate substrate and successfully realized the detection of the human pulse signal. This work provides a new strategy for obtaining high-performance panchromatic PM-OPDs by designing device structures and selecting appropriate materials.

Enhancement of the photoconversion efficiency of Sb2S3 based solar cell by overall optimization of electron transport, light harvesting and hole transport layers

In thin-film photovoltaic, Sb2S3 is a leading absorber material due to its broad-band optical response and excellent electrical properties, with the highest reported efficiency in the planar Sb2S3 configuration being 8 %. By simulations, optimized parameters for each component of the n-i-p FTO/ETL/Sb2S3/HTL/Au planar heterojunction device, as well as a photoconversion efficiency (PCE-η) of 28.64 % under an AM 1.5G spectral irradiance, have been predicted. In this report, we systematically optimized the electron transport layer (ETL), light harvesting layer (Sb2S3), and hole transport layer (HTL) separately based on theoretically predicted values in order to understand the effect of each component and optimize solar cell performance. The optimized results showed that simply optimizing the ETL, Sb2S3 layer, and HTL resulted in achieving the efficiency ∼4.11 % and to achieve the theoretically predicted device performance, a precise control of intrinsically formed traps, the presence of surface defect states, and lattice dislocations in Sb2S3, are important as these factors are found to be the main factors that enhance charge carrier recombination, slow charge transfer across the interface, and charge carrier mobility.

Device Modelling and Optimization of Nanomaterial-Based Planar Heterojunction Solar Cell (by Varying the Device Dimensions and Material Parameters).

The objective of this work is to model a multi-disciplinary (multi-physics) organic photovoltaic (OPV) using mathematical modeling and analyzing the behavior of a standard planar heterojunction (PHJ) or bi-layer thin-film photovoltaic device, supporting the optimization of an efficient device for future production and assisting in evaluating and choosing the materials required for the efficient device. In order to increase photodiode performance, the device structure and geometrical properties have also been optimized and evaluated. In this work, the effects of varying the device size and transport parameters on the performance parameters of a PHJ OPV structure comprised of Indium Tin Oxide as the anode (ITO), semiconducting single-wall carbon nanotube (s-SWCNT) as the donor, fullerene C70 as the acceptor, and Aluminium (Al) as the cathode have been analyzed. The conclusion suggests that a highly effective ITO/s-SWCNT/C70/Al PHJ solar cell may be fabricated if the suggested device is appropriately built with a thin layer and a high exciton diffusion length, bi-molecular recombination coefficient, and improved mobility charge carriers, in particular hole mobility in the cell’s donor layer. In addition, the displayed current–voltage (I–V) characteristics of the proposed PHJ device are clearly indicated, with the ITO/s-SWCNT/C70/Al combination having the greatest short-circuit current density (Jsc) value of 5.61 mA/cm2, open-circuit voltage (Voc) of 0.7 V, fill factor (FF) of 79% and efficiency (ɳ) of 3.1%. Results show that the electrical performance of organic solar cells is sensitive to the thickness of the photoactive substance. These results open the path for developing inexpensive and highly efficient solar cells.

Double-Side Selective Spectral Response Organic Photodetectors for Demultiplexing Optical Signals.

Selective spectral response photodetectors (PDs) capable of accurately capturing the color of images have broad applications in industry and academia. Here, we demonstrate filter-free, wavelength-selective detection organic photodetectors (OPDs) with two distinct response ranges and having the planar bilayer heterojunction device structure by employing either a (semi-)transparent anode or a cathode as the incident light window. The resultant OPDs exhibit a responsivity of 51 mA W-1 in the range 300-650 nm and 11 mA W-1 in the range 650-850 nm under top illumination condition. Similarly, the devices show a responsivity of 2 mA W-1 for the short-wavelength region and 131 mA W-1 for the long-wavelength region when under bottom illumination condition, indicating a high responsivity ratio that meets the requirements for selective detection. Hence, our individual device not only works in either visible or NIR range but also provides narrowband detection with spectral widths down to 100 nm in the NIR range. The working mechanism of spectral selectivity is identified through quantitative analysis of the external quantum efficiency (EQE) spectra using optical modeling when compared to the OPDs with bulk heterojunction structure, thus clarifying the general validity of the device design concept. Finally, our OPDs can demultiplex intermixed optical signals from the light-communication system successfully. Our results should inspire new studies on the device design concept and new applications of OPDs.

Overcome energy loss of exciplex-sensitized fluorescence OLEDs with separating exciton generation and fluorescence emission zone

TADF-sensitizing-fluorescence (TSF) strategy suffered a disturbing energy loss causing by the T1 states of fluorescence dopant (FD) due to its low T1-state energy and forbidden of radiative transition. In this manuscript, we used TCTA/PO-T2T planar heterojunction (PHJ) interface as exciton generation zone and adjacent PO-T2T layer doped with rubrene as fluorescence emission zone, achieved the maximum EQE and CE of 8.3% and 26.1 cd A−1, respectively for rubrene-based device. Our experiments show the necessary PO-T2T thickness doped with rubrene is 15 nm and thicker doping layer over 15 nm would destroy device efficiency. It was further found that the exciplex exciton begin to decay within the time of 4 nm diffusion distance in PO-T2T layer and most of exciplex excitons were restrained in TCTA/PO-T2T heterojunction interface in PHJ device. The about 1.1 eV barrier for hole injection from TCTA to PO-T2T and bad hole-transporting capability of PO-T2T made exciple exciton only generate on this interface. Thus, even if the rubrene doped PO-T2T layer is right after the TCTA layer, FD in PO-T2T layer are well separated to the exciplex excitons in TCTA/PO-T2T interface, overcoming T1 energy loss caused by FD. Our approach provides a beneficial path towards overcome energy loss causing by the T1 states of FD in TSF-OLEDs based on exciplex as TADF sensitizer.

Low-Temperature Solution-Processed Cu2AgBiI6 Films for High Performance Photovoltaics and Photodetectors

Recently, Cu2AgBiI6 semiconductor has been investigated due to the high absorption coefficient, direct bandgap, and low exciton binding energy, which are promising for eco-friendly photoelectric devices. Herein, pyridine is introduced as solvent additive to completely dissolve the solutes and form clear Cu2AgBiI6 precursor solution, which results in high-quality films and may provide a general approach for high-quality film growth of other bismuth-based metal halide semiconductors. In addition, the electronic structure of Cu2AgBiI6 has been demonstrated for the first time and shows an intrinsically weak n-type semiconductor. Furthermore, phenethylammonium iodide for surface passivation significantly improves the film quality, slightly n-dopes the material, and shifts up the band level. Finally, the photovoltaics and photodetector performance for n-i-p planar heterojunction devices have been investigated. The efficiency is up to 1%, highest for Cu2AgBiI6 solar cells and comparable with other lead-free bismuth based metal halide solar cells. Moreover, photodetectors with fast speed of rising and decaying time, especially the excellent specific photodetectivity of ∼1012 Jones within the wavelength of ∼350-600 nm, are achieved, which paves an alternative and promising strategy for the design of future commercial photodetectors that are self-powered, stable, nontoxic, etc.

Enhanced proton irradiation resistance in Cs-doped CH3NH3PbI3 films and solar cells

Mixed-cation perovskite solar cells have attracted tremendous attention in space applications due to their excellent power conversion efficiency (PCE) and stability to light and heat. Although the evolution of photovoltaic performance in different space environments has been investigated, the role of inorganic cesium ions (Cs+) in the enhancement of irradiation resistance needs to be further clarified. Herein, the structure and performance evolution of Cs-doped CH3NH3PbI3 (MAPbI3) films and planar heterojunction devices under proton irradiation up to 1 × 1016 p cm−2 were studied. 5% of Cs+ doping can increase the cohesive energy of MAPbI3 and effectively alleviate the lattice strain induced by proton irradiation, thereby enhancing the crystallinity and stability of films. The bandgap changes of irradiated Cs0.05MA0.95PbI3 films under the identical fluence were only one third of that of MAPbI3 films. Upon irradiation under the fluence of 1 × 1014 p cm−2, the density of trap states in the undoped and 5%Cs-doped films increased by 71% and 9%, respectively, and the average PCE of 20 corresponding devices decreased only by 12% and 9%, respectively. This proves that the replacement of organic methylamine ion with inorganic cesium ion contributes to the improvement of MAPbI3 resistance to proton irradiation, thus confirming the application prospects of mixed-cation or all-inorganic perovskite solar cells in spacecraft.

ZrSnO4: A Solution-Processed Robust Electron Transport Layer of Efficient Planar-Heterojunction Perovskite Solar Cells

A robust electron transport layer (ETL) is an essential component in planar-heterojunction perovskite solar cells (PSCs). Herein, a sol-gel-driven ZrSnO4 thin film is synthesized and its optoelectronic properties are systematically investigated. The optimized processing conditions for sol-gel synthesis produce a ZrSnO4 thin film that exhibits high optical transmittance in the UV-Vis-NIR range, a suitable conduction band maximum, and good electrical conductivity, revealing its potential for application in the ETL of planar-heterojunction PSCs. Consequently, the ZrSnO4 ETL-based devices deliver promising power conversion efficiency (PCE) up to 19.05% from CH3NH3PbI3-based planar-heterojunction devices. Furthermore, the optimal ZrSnO4 ETL also contributes to decent long-term stability of the non-encapsulated device for 360 h in an ambient atmosphere (T~25 °C, RH~55%,), suggesting great potential of the sol-gel-driven ZrSnO4 thin film for a robust solution-processed ETL material in high-performance PSCs.

Strongly Reduced Non-Radiative Voltage Losses in Organic Solar Cells Prepared with Sequential Film Deposition.

With nearly 100% yields for mobile charge carriers in organic solar cells (OSCs), the relatively large photovoltage loss (ΔVoc) is a critical barrier limiting the power conversion efficiency of OSCs. Herein, we aim to improve the open-circuit voltage (Voc) in OSCs with non-fullerene acceptors via sequential film deposition (SD). We show that ΔVoc in planar heterojunction (PHJ) devices prepared by the SD method can be appreciably mitigated, leading increases in Voc to 80 mV with regard to the Voc of bulk heterojunction devices. In PHJ OSCs, the energy level of intermolecular charge-transfer states is found to increase with a decrease in the level of aggregation in the solid state. These properties explain the enhanced electroluminescent quantum efficiency and resultant suppression of the voltage losses induced by nonradiative charge recombination and interfacial charge transfer. This work provides a promising strategy for tackling the heavily discussed photovoltage loss in OSCs.

All‐Green Solvent‐Processed Planar Heterojunction Organic Solar Cells with Outstanding Power Conversion Efficiency of 16%

AbstractDevice engineering is an effective way to improve the photovoltaic performance of organic solar cells (OSCs). Currently, the widely used bulk heterojunction (BHJ) structure has problems such as material solubility limitations and the emerging pseudoplanar heterojunction (PPHJ) structure is also troubled by printing technology requirements. However, these issues can be solved by the reasonable application of traditional planar heterojunction (PHJ) structure. Herein, PM6:BO‐4F system is selected to prepare PHJ devices by combining sequential spin‐coating and orthogonal solvent strategy. In view of the good solubility of PM6 and BO‐4F in commonly used high‐boiling solvent chlorobenzene (CB) and green solvent tetrahydrofuran (THF), respectively, the PHJ devices are successfully prepared by using these two orthogonal solvents, achieving a power conversion efficiency (PCE) of 15.6%. On this basis, green nonhalogen reagent o‐xylene (O‐XY) is further used to process PM6. Due to the large polarity difference between O‐XY and THF, all‐green solvent‐processed PHJ devices are successfully fabricated and obtain an astonishing PCE of 16%. As far as it is known, it is the highest efficiency for PHJ OSCs. The results prove the huge research potential of PHJ structure and point out new direction for solving OSC materials compatibility, long‐term stability, and future commercial applications.

Solution processed AgSbS2 film for efficient planar heterojunction solar cells

AgSbS2 is a promising absorber material for photovoltaic cells because of its optimum bandgap, strong optical absorption, and excellent stability. Here, we report a spin-coating and annealing approach for the fabrication of AgSbS2 solar cells, where Ag-Sb-thiourea complex solution was prepared as the precursor solution. We identified that the annealing temperature crucially affected the phase composition, crystallinity, and surface morphology of the AgSbS2 film. We also probed the electronic structures and established a FTO/TiO2/AgSbS2/Spiro-OMeTAD/Au device structure. This device finally achieved an encouraging power conversion efficiency of 2.25%, which is highest efficiency in AgSbS2 solar cells. Our research opens up another prospect for pursuing high performance AgSbS2 thin film solar cells by adopting a solution processing method and planar heterojunction device structure.

The optoelectronic behavior of reduce graphene oxide-carbon nanotube nanocomposites

Graphene-carbon nanotubes (CNTs) nanocomposites hold tremendous potential to offer more innovative and cost-effective electronic technologies. In this study, type of CNTs employed to form composites with reduced graphene oxide (rGO) were single walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), and mixed CNTs (blends of SWCNTs and MWCNTs). The composites were further utilized to fabricate the planar heterojunction devices. Field emission scanning electron microscopy, UV-Vis and Raman spectroscopy of the synthesized nanocomposites were performed to investigate the surface morphology, absorption behavior and structure, respectively. On comparing the optoelectronic performance of devices, we found that mixed CNTs-rGO nanocomposite-based devices exhibited greater responsivity and detectivity compared to those of SWCNTs and MWCNTs based devices. The superior performance is mainly ascribed to the better immunity of the mixed CNTs-rGO nanocomposite-based devices against the charge recombination due to the better interface quality and lesser interface defects, as inferred from the dark current analysis and impedance spectroscopy analysis. This work demonstrates the great potential of mixed CNTs-rGO composites as an active layer material for optoelectronic applications.

Innovative Implementation of an Alternative Tetrathiafulvene Derivative for Flexible Indium Phthalocyanine Chloride-Based Solar Cells.

Herein, we present the photovoltaic properties of an indium phthalocyanine chloride (InClPc)-based flexible planar heterojunction device, introducing the tetrathiafulvene derivative 4,4′-Dimethyl-5,5′-diphenyltetrathiafulvalene (DMDP-TTF) as the electron donor layer. UV-vis spectroscopy is widely used to characterize the electronic behavior of the InClPc/DMDP-TTF active layer. The interactions between the DMDP-TTF and phthalocyanine are predominantly intermolecular and the result of the aggregation of InClPc. Tauc bands were obtained at 1.41 and 2.8 eV; these energy peaks can result in a charge transfer ascribed to the transition from the DMDP-TTF to π-orbitals that are associated with the phthalocyanine ring or even with the same indium metal center. Conductive carbon (CC) was used for the cathode. Finally, an indium tin oxide (ITO)/InClPc/DMDP-TTF/CC device was fabricated by high-vacuum thermal evaporation onto a flexible substrate and the photovoltaic properties were evaluated. A diode type I-V curve behavior was observed with a photovoltaic response under illumination. A generated photocurrent of 2.25 × 10−2 A/cm2 was measured. A conductivity reduction with the incident photon energy from 1.61 × 10−7 S/cm to 1.43 × 10−7 S/cm is observed. The diode resistance presents two different behaviors with the applied voltage. A VTFL of 5.39 V, trap concentration of 7.74 × 1016 cm−3, and carrier mobility values of ~10−6 cm2/V s were calculated, showing improved characteristics via the innovative implementation of an alternative TTF-derivative, indicating that the DMDP-TTF has a strong interaction at the junction where free available states are increased, thus inducing higher mobilities due to the large number of π-orbitals, which indicates the feasibility of its use in solar cells technology.

Overcoming incompatibility of donors and acceptors by constructing planar heterojunction organic solar cells

Nanoscale phase separation plays a critical role in achieving high photovoltaic performance in bulk-heterojunction organic solar cells, which is limited by solubility, crystallinity, and the compatibility of the donors and acceptors. However, these limits can be overcome by new applications of the traditional planar heterojunction structure. Herein, we demonstrate quasi-orthogonal solvents for a wide-band-gap donor (P2F-EHp) and a highly crystalline non-fullerene acceptor (M4–4F) to overcome the over-agglomeration and enabled the fabrication of a planar heterojunction device with a favorable power conversion efficiency of 14.2% (compared with 12.7% in bulk-heterojunction device), which is among one of the highest efficiencies of planar heterojunction devices to date. Detailed studies based on cross-sectional transmittance electron microscopy, grazing incidence wide-angle X-ray scattering at various incident angles, and resonance soft X-ray scattering measurements confirmed the formation of optimal nanoscale morphology. Further transient absorption measurements also proved that the exciton dissociation and free-carrier generation efficiency are not limited by the small mixed-phase area and large pure domains. These findings show insights into the intrinsic morphological changes and charge transfer process in bulk-heterojunction and planar heterojunction structures, providing a novel method for matching donors and acceptors with relatively poor compatibility. • Comparing absorption, morphology, and charge carrier dynamics of BHJ and PHJ devices. • Introducing an effective approach to construct OSCs using poorly compatible donors and acceptors. • Demonstrating the possibility of obviating the need for bulk-heterojunction structure.

Efficient coaxial n-i-p heterojunction Sb2S3 solar cells

Sb2S3 is a kind of emerging light harvesting material for solar cell applications, where both planar and nanostructured configurations are of great interests in the device investigations. This work conducts a comparative study on heterojunction configuration of Sb2S3 solar cells with regard to different CdS substrates. By controlling the hydrothermal durations of Sb2S3 film, the CdS nanorod enables the fabrication of coaxial n-i-p heterojunction Sb2S3 solar cells. It is demonstrated that coaxial heterojunction can effectively improve carrier transport compared with planar heterojunction, leading to the fill factor increasing from 51.3% to 62.7% with regard to different degree of pore filling. Mechanism investigations suggest that both deep-level defect type and defect density in coaxial heterojunction device are significantly reduced, which further reduces carrier recombination in Sb2S3 film, clearly manifesting that the coaxial heterojunction configuration reduces the series resistance and enables efficient carrier transport. In addition, the coaxial heterojunction device presents a remarkably improved stability compared with planar heterojunction device. The research offers a fundamental guideline for the fabrication of efficient antimony chalcogenide solar cells.

Boosting the performance of planar inverted perovskite solar cells employing graphene oxide as HTL

The numerical simulation tool SCAPS-1D was used to analyze perovskite solar cell having the architecture ITO/ PEDOT:PSS or GO /CH3NH3PbI3-xClx/ PCBM /Au contains inverted planar hetero-junction device. In this work, we investigated the effect of inserting the Graphene Oxide (GO) as Hole Transport layer (HTL) on the performance of perovskite solar cells. Simulation results show that the use of GO as a hole transport layer is efficient. The efficiency of PSCs based on GO HTL was increased by about 1.6 % compared to the conventional PEDOT:PSS HTL device. The obtained results of optimizing the thickness of GO HTL exhibited an optimum value around 10 nm with an efficiency of 12.35 %, Voc of 1.19 V and FF of 54.8 %. We have also shown that the performance of device for high GO carrier density is a better than with low ones. In addition, increasing the temperature beyond the optimum value obtained around 320 K for both HTL materials (GO and PEDOT:PSS) has detrimental effect on the performance of the perovskite solar cells however the device is more sensitive to the temperature with PEDOT:PSS than the GO ones. The effect of band gap of GO on the performance of device is also studied. The obtained results underline the determining role playedby this parameter with an optimum value around 3.25 eV.

Photomultiplication type near‐infrared organic photodetectors with a mixed active layer

AbstractPhotomultiplication type near‐infrared (NIR) organic photodetectors (OPDs) are constructed with lead phthalocyanine (PbPc) and C60 acted as the donor and acceptor, respectively. Compared with the PbPc/C60 planar heterojunction device, the PbPc:C60 mixed active layer devices show enhanced NIR responses. The optimized mixed active layer device displays an external quantum efficiency (EQE) of 22.8% at 870 nm under zero bias, which is about 45% higher than that of planar heterojunction device. Moreover, it also presents a detectivity in the order of 1012 Jones and an EQE of 400% under applied bias of −8 V, indicating a photocurrent gain obtained in the device. Although the mixed active layer devices have a lower absorption in the NIR region, the donor: acceptor mixed structure increases the donor/acceptor contact area and forms continuous carrier transport paths, which increases the excitons dissociation efficiency and the photogenerated carriers collection efficiency and hence the response of the devices.