Hybrid Planar-mixed Heterojunction Research Articles

Improved performance of perovskite photodetectors with a hybrid planar-mixed heterojunction

Improved performance of lateral perovskite photodetectors is demonstrated based on a hybrid planar-mixed heterojunction structure, which comprises a CH3NH3PbI3:PC61BM ([6,6]-phenyl-C61-butyric acid methyl ester) bulk heterojunction on a planar SnO2 layer. The photodetector with an optimized PC61BM doping concentration shows a photocurrent more than three times to that device without a PC61BM doping or without a planar SnO2 layer, confirming that the hybrid planar-mixed heterojunction structure plays an important role in improving the performance of the devices. The photodetector exhibits a responsivity higher than 2 A W−1 in a wide range from ultraviolet to near infrared with a maximum one of 9 A W−1 at 315 nm. The improved performance is not only attributed to the increased electron transporting ability and the dissociation probability of excitons and/or electron-hole pairs in perovskite, but also to the growth of compact perovskite films with decreased grain boundary and hence the increased charge carriers transporting efficiency due to the introduction of PC61BM.

Investigation of post-thermal annealing-induced enhancement in photovoltaic performance for squaraine-based organic solar cells

In this work, we have systematically investigated the post-thermal annealing-induced enhancement in photovoltaic performance of a 2,4-bis[4-(N, N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (DIBSQ)/C60 planar heterojunction (PHJ) organic solar cells (OSCs). An increased power conversion efficiency (PCE) of 3.28% has been realized from a DIBSQ/C60 device with thermal annealing at 100 °C for 4 min, which is about 33% enhancement compared with that of the as-cast device. The improvement of the device performance may be mainly ascribed to the crystallinity of the DIBSQ film with post-thermal annealing, which will change the DIBSQ donor and C60 acceptor interface from ^PHJ to hybrid planar-mixed heterojunction. This new donor-acceptor heterojunction structure will significantly improve the charge separation and charge collection efficiency, as well as the open circuit voltage (Voc) of the device, leading to an enhanced PCE. This work provides an effective strategy to improve the photovoltaic performance of SQ-based OSCs.

The effects of mixture ratios of CuPc:C60 in nanostructured organic hybrid planar–mixed heterojunction photovoltaic cells

Efficient organic hybrid planar–mixed heterojunction photovoltaic cells based on copper phthalocyanine (CuPc) and fullerene (C60) were fabricated. This structure, in addition to the high efficiency in exciton diffusion of a mixed heterojunction, has low resistance in charge transporting of a planar heterojunction. The effects of different CuPc:C60 mixing ratios in two stages and by varying the CuPc and C60 thicknesses, respectively, were investigated. Also, we illustrate the charge transport mechanisms and specify the charge injection models for the cells. For the optimized cell, trap-charge-limited current (TCLC) model was dominant. MoO3 is one of the common materials as anodic buffer layer which is used for modifying the ITO electrode and improving the charge extraction. According to the AFM results, after depositing MoO3 layer on ITO, the surface root mean square (RMS) roughness decreases from 8.31 to 4.14 nm. Optimal thickness for both CuPc and C60 layers was obtained 20 nm. Finally, the greatest value in power conversion efficiency was achieved 3.81% using the 1:1 CuPc:C60 mixing ratio. Moreover, short-circuit current density (Jsc), fill factor (FF), and open-circuit voltage (Voc) for this optimized cell were found 10.21 (mA/cm2), 0.64 (V), and 0.58, respectively.

Inverted, semitransparent small molecule photovoltaic cells

We demonstrate semitransparent small molecule organic photovoltaic (OPV) cells based on inverted mixed and hybrid planar-mixed heterojunction (PM-HJ) structures comprised of a neat acceptor layer located beneath the donor/acceptor mixed region. The fill factor increases from 0.53 ± 0.01 for the mixed HJ to 0.58 ± 0.01 for the PM-HJ due to reduced series resistance, whereas the internal quantum efficiency increases from an average of 75% to 85% between the wavelengths of λ = 450 nm and 550 nm. The inverted, semitransparent PM-HJ cell achieves a power conversion efficiency of PCE = 3.9% ± 0.2% under simulated AM1.5G illumination at one sun intensity with an average optical transmission of T¯ = 51% ± 2% across the visible spectrum, corresponding to > 10% improvement compared with the mixed HJ cell. We also demonstrate an inverted semitransparent tandem cell incorporating two PM-HJ sub-cells with different absorption spectra. The tandem cell achieves a PCE = 5.3% ± 0.3% under simulated AM1.5G at one sun intensity with T¯ = 31% ± 1% across the visible. Almost identical efficiencies are obtained for tandem cells illuminated via either the cathode or anode surfaces.

Small-Molecule Planar-Mixed Heterojunction Photovoltaic Cells with Fullerene-Based Electron Filtering Buffers

An electron filtering buffer with high electron mobility and efficient exciton-blocking is employed in a hybrid planar-mixed heterojunction solar cell. The novel buffer can significantly reduce bimolecular recombination and exciton-polaron quenching, leading to a small-molecule photovoltaic cell with a power conversion efficiency of 8.1% ± 0.4% under 1 sun illumination.

A hybrid planar-mixed tetraphenyldibenzoperiflanthene/C70 photovoltaic cell

We describe a hybrid planar-mixed heterojunction (PM-HJ) organic photovoltaic cell based on tetraphenyldibenzoperiflanthene (DBP) and C70 with a power conversion efficiency of up to 6.4% ± 0.3%. Optimized cells consist of a DBP:C70 mixed layer at a volume ratio of 1:8 and a 9-nm thick C70 cap layer. The external quantum efficiency (EQE) in the visible of the PM-HJ cell is up to 10% larger than the mixed-HJ cell that lacks a C70 acceptor cap layer. The improvement in EQE is attributed to reduced exciton quenching at the MoO3 anode buffer layer surface. This leads to an internal quantum efficiency >90% between the wavelengths of λ = 450 nm and 550 nm, suggesting efficient exciton dissociation and carrier extraction in the PM-HJ cell. The power conversion efficiency under simulated AM 1.5G, 1 sun irradiation increases from 5.7% ± 0.2% for the mixed-HJ cell to 6.4% ± 0.3% for the PM-HJ cell, with a short-current density of 12.3 ± 0.3 mA/cm2, open circuit voltage of 0.91 ± 0.01 V, and fill factor of 0.56 ± 0.01.

Donor-acceptor small molecule with coplanar and rigid π-bridge for efficient organic solar cells

A novel donor–acceptor (D–A) donor molecule, 1, comprising of two di-p-tolylamino donors and a dicyanovinylene acceptor bridged by a planar and rigid fluorene moiety has been synthesized and characterized. The molecular structure and crystal packing of 1 was characterized by single-crystal X-ray crystallography. Such molecular configuration endowed 1 with an efficient D–A interaction, rendering an intense ICT absorption band for efficiently light-harvesting and retain low-lying HOMO for generating sufficient open-circuit voltage (Voc). The vacuum-deposited hybrid planar-mixed heterojunction (PMHJ) photovoltaic devices utilizing 1 as donor and C70 as acceptor to achieve power conversion efficiencies (PCEs) of 4.04 and 5.31% for the single- and tandem-cell photovoltaic devices under simulated AM 1.5 illumination (100mWcm−2).

Fabrication and Characteristics of Fullerene–Perylene Dyad Based Organic Photovoltaic Cell

Fullerene is an acceptor material which is used most usually in organic photovoltaic cell. By the way, the reduction of electron mobility and the phase separation of conducting polymer and fullerene in the actual bulk heterojunction photovoltaic cell limit further improvement of device performance. In order to overcome the problems, fabrication of hybrid planar mixed heterojunction cells and synthesis of donor-acceptor dyad have been studied. In the present work, we have synthesized fullerene-perylene dyad to improve the fullerene based photovoltaic cell. In order to explore the properties of the synthesized material, the measurements of absorption spectrum and energy level were carried out. We have investigated the energy conversion efficiency of organic photovoltaic cell consisting of ITO/PEDOT-PSS/MEH-PPV:fullerene-perylene dyad/Al.

High speed responsive near infrared photodetector focusing on 808 nm radiation using hexadecafluoro–copper–phthalocyanine as the acceptor

We have demonstrated an organic photodetector (PD) which can detect 808 nm radiation in near infrared (NIR) region. The photodiode has a hybrid planar-mixed heterojunction structure: ITO/CuPc (10 nm)/CuPc:F16CuPc (1:2, 30 nm)/F16CuPc (20 nm)/LiF (1 nm)/Al. Here, CuPc and F16CuPc denote copper–phthalocyanine and hexadecafluoro–copper–phthalo-cyanine complexes, respectively. The photodiode behaves a response time of 80 ns and a bandwidth of 14 MHz, which are higher than those of recent reports. At the same time, the response waveband of the photodiode covers longer wavelength in NIR comparing to the PD reported. It is conjectured that the high detection performance is due to high electron-mobility of F16CuPc, the large band edge offset between D/A molecules as well reasonable design of the diode structure. The detail working mechanism is also augured.

Mixed donor-acceptor molecular heterojunctions for photovoltaic applications. II. Device performance

We demonstrate efficient organic photovoltaic cells employing a photoactive region composed of a mixed donor-acceptor molecular layer, the properties of which were introduced in the preceding paper (Part I) [Rand et al., J. Appl. Phys. 98, 124902 (2005)]. The hybrid planar-mixed heterojunction (PM-HJ) device architecture consists of a film mixture of donor and acceptor molecules inserted between layers of pure donor and acceptor composition. Using the donor, copper phthalocyanine, and the acceptor, C60, we demonstrate a hybrid PM-HJ cell with a maximum power conversion efficiency of (5.0±0.3)% under 1–4suns simulated AM1.5 solar illumination. The current-voltage characteristics of the PM-HJ cell are described using a model based on the field-dependent charge collection length.

Mixed donor-acceptor molecular heterojunctions for photovoltaic applications. I. Material properties

In this and the following paper (Parts I and II, respectively), we discuss the properties of mixed donor-acceptor organic thin films and their application to organic solar cells. In Part I, we present a study of the material properties of mixed donor-acceptor thin films. Through optical absorption, x-ray diffraction, microscopy, and charge transport measurements, we determine the relationships among film microstructure, mixing ratio, and charge conduction in mixtures of two organic molecular species. We find that mixed layers of the molecular pair of 1:1 (by weight) copper phthalocyanine in C60 have electron and hole mobilities reduced by more than one order of magnitude compared to corresponding films of pure composition. In Part II, we demonstrate that the performance of organic hybrid planar-mixed heterojunction photovoltaic cells based on a mixed donor-acceptor molecular layer sandwiched between the donor and acceptor layers of homogeneous composition can have improved performance over conventional planar heterojunction cells containing no mixed composition layers.