Space Charge Limited Current Research Articles

Enhancing photovoltaic performance of perovskite solar cells utilizing germanium nanoparticles

Morphological and crystalline control over hybrid organic-inorganic perovskite films is pivotal for efficient photovoltaic (PV) performance devices. Yet, this remains very challenging for solution processed perovskite solar cells (PVSCs), especially mesoscopic PVSCs, due to the complicated crystallization kinetics of hybrid semiconductor materials within dynamic spin-coating and post annealing. In this work, colloidal Ge nanoparticles (NPs) were added onto a mesoporous TiO2 (m-TiO2) electron transporting layer (ETL) to regulate perovskite crystal growth. Systematic investigation and optimization disclose that incorporation of an appropriate ratio of Ge NPs onto the m-TiO2 ETL can simultaneously increase the size of the CH3NH3PbI3 crystals, decrease the number of the grain boundaries and promote the interfacial properties of perovskite/m-TiO2. The related mechanisms are clarified through detailed morphology and crystal structure analyses. The electron mobility of the perovskite absorber, determined using the space charge limited current (SCLC) method, was increased by over 5 times when an optimized amount of Ge NPs were employed. Average power conversion efficiency (PCE) of 18.59% was achieved from 16 cells and the best PCE of 19.6% was attained via the addition of the optimized amount of Ge NPs. We study the fundamentals of optics and physics behind the PVSC device based on the high refractive index Ge NPs. This work offers an innovative scenario to enhance the performance of perovskite based optoelectronics by employing optically stable, chemically inert, low-cost and green semiconductor NPs.

Low-temperature in-situ preparation of ZnO electron extraction layer for efficient inverted polymer solar cells

Abstract The facile in-situ fabricated interfacial layers for highly efficient and stable polymer solar cells (PSCs) have garnered extensive attention. Herein, low-temperature in-situ prepared ZnO derived from zinc acetylacetonate (Zn(acac) 2 ) is used as electron extraction cathode interfacial layer (CIL) in inverted PSCs. The chemical component, optical features, electron mobility and charge transfer properties of the low-temperature in-situ obtained ZnO CIL are detailedly studied by X-ray photoelectron spectroscopy (XPS), ultraviolet visible (Uv–vis) spectra, space charge limited current (SCLC) and time-resolved photoluminescence (TRPL) measurements, respectively. The obtained ZnO layer demonstrates outstanding optical and electrical properties. Via fine-tuning the parameters of film processing, a record high power conversion efficiency (PCE) up to 11.65% is obtained for PBDB-T:IT-M-based PSCs, indicating ZnO significantly facilitates carrier transportation and induces fast charge transfer to electrode. The low-temperature in-situ prepared ZnO CIL can be further applied into the large-area and flexible PSCs.

The Effect of Surface on Conductivity of PbSnTe:In/BaF2 Topological Crystalline Insulator in Space Charge Limited Current Regimes

The effect of surface chemical treatment on current-voltage (IV) characteristics of high-resistance MBE-grown PbSnTe:In films in space charge limited current (SCLC) regimes has been studied. At T=4.2 K depending on surface chemical treatment the current in films in SCLC regimes under no illumination could rise up to 104 times and even more. The surface chemical treatment also affected both the value and behavior of the photocurrent. The qualitative model for the observed phenomena has been discussed.

Dielectric and ferroelectric properties of CoCr2O4 nanoceramics

CoCr2O4 nanoceramics are prepared by sol–gel auto combustion method. Synchrotron X-ray diffraction analysis affirms the single-phase pristine cubic structure with space group [Formula: see text]. Debye–Scherrer method estimates the crystallite size of main intense peak to be [Formula: see text][Formula: see text]nm. Prominent bands obtained in infrared spectra at 448 and 599[Formula: see text]cm[Formula: see text] are due to metal–oxygen stretching bond present at tetrahedral and octahedral sites. Dielectric parameters decrease as frequency increases from [Formula: see text] to [Formula: see text][Formula: see text]Hz that can be interpreted by Maxwell–Wagner-type interfacial polarization. Complex impedance spectra (Nyquist plot) reveal arc like behavior, which is mainly due to intergrain (grain boundary) resistance that also exhibits conducting nature of the nanoceramics. Weak ferroelectricity is mainly associated with the partial reversal of the polarization. Leakage current behavior follows the Ohmic and Child square law. Electron conduction process was interpreted by space-charge limited current (SCLC) mechanism. Leakage current behavior observed in cobalt chromite nanoceramics is mainly attributed to the oxygen vacancies.

Effects of (0.01Ni-PVA) interlayer, interface traps (Dit), and series resistance (Rs) on the conduction mechanisms(CMs) in the Au/n-Si (MS) structures at room temperature

In order to determine effects of interlayer, Dit, and Rs on the CMs, both Au/n-Si and Au/(0.01Ni-PVA)/n-Si (MPS) structures were fabricated on the n-Si wafer and their electrical parameters were extracted from the current-voltage (I-V) and capacitance-voltage (C-V) measurements. The ideality factor (n), zero-bias barrier height (ΦBo), rectifying rate (RR at ±5V), Rs, shunt resistances (Rsh), and density of Dit (at 0.40eV) values were found from the I-V data as 1.944, 0.733 eV, 3.50×103, 64.8 , 0.23 M, 1.62x1013 eV-1cm-2 for MS and 1.533, 0.818 eV, 1.15×107, 5.0 , 57.5 M, 8.82x1012 eV-1cm-2 for MPS. Fermi energy (EF), barrier height (ΦB(C-V)), depletion-layer width (WD) values were obtained from the C-V data as 0.239 eV, 0.812 eV, 1.14x10-4 cm for MS and 0.233 eV, 0.888 eV, 9.31x10-5 cm for MPS. These results indicated that the MPS structure has lower Rs, Dit, leakage current and higher RR, Rsh, BH compared with MS and so this interlayer can be successfully used instead of conventional insulator interlayer. The Ln(I)-Ln(V) plot at forward-bias region has three linear parts corresponding to the low, intermediate, and higher voltages. In these regions; conduction mechanism (CM) is governed by ohmic, trap charge-limited current (TCLC) and space charge-limited current (SCLC), respectively.

Low Temperature‐Processed Stable and Efficient Carbon‐Based CsPbI2Br Planar Perovskite Solar Cells by In Situ Passivating Grain Boundary and Trap Density

Improvement in stability and an economical processing technique are the main aspects of the commercialization of perovskite solar cells (PSCs). In this study, a 425 nm‐thick CsPbI2Br film with a high crystalline, smooth, and uniform surface morphology is obtained by Pb(SCN)2 passivating the grain boundaries under low temperature (150 °C). The results of a series of electrochemical analyses, including space‐charge‐limited‐current (SCLC), open‐circuit voltage decay (OCVD), electrical impedance spectroscopy (EIS), intensity‐modulated photocurrent spectroscopy (IMPS), and intensity‐modulated photovoltage spectroscopy (IMVS), demonstrate that the trap density of the CsPbI2Br film is greatly reduced with Pb(SCN)2, which effectively inhibits the interface recombination and promotes charge transport in CsPbI2Br PSC. Efficiencies of 12.22% and 10.44% are achieved for low‐temperature‐processed CsPbI2Br planar‐architecture PSCs with ITO/SnO2/CsPbI2Br/ poly(3‐hexylthiophene) (P3HT)/Ag and ITO/SnO2/CsPbI2Br/carbon, respectively. This low‐cost, high‐efficiency carbon‐based inorganic PSC shows potential industrial application, especially for tandem solar cells.

Relativistic Charged-Particle Beam Space-Charge Limited Current in Finite Length Coaxial Drift Tube

In the strong axial (guide) magnetic field and uniform beam density approximations, we calculate scalar potential distribution induced by axisymmetric annular relativistic charged-particle beam in a finite-length coaxial drift tube. This scalar potential distribution allows us to find an approximate radial position at which the extremum of the scalar potential is attained in the coaxial drift tube inside the annular relativistic charged-particle beam. By knowing the approximate extremal radial position, we obtain the analytical estimate for the space-charge limited (SCL) current of axisymmetric annular (finite thickness) relativistic charged-particle beam propagating in strong axial magnetic field in a finite length coaxial drift tube and establish a simple correspondence of this result to that in a long coaxial drift tube. A comparison of numerical nonlinear calculations and the analytical estimate for the SCL current in the finite-length coaxial drift tube is also given.

Highly bright Li(Gd,Y)F4:Yb,Er upconverting nanocrystals incorporated hole transport layer for efficient perovskite solar cells

We report synthesis of highly bright Li(Gd,Y)F4:Yb,Er upconversion (UC) nanophosphors and integrate them into the hole transport layers (HTLs) to examine their optical and electrical effects in perovskite solar cells (PSCs). Mono-disperse, single tetragonal-phase Li(Gd,Y)F4:Yb,Er upconversion nanocrystals (UCNCs) were prepared by a thermal decomposition method. The grown Li(Gd,Y)F4:Yb,Er UCNCs displayed tetragonal bipyramidal morphologies and intense UC green luminescence. The octahedral UCNCs were blended into the Spiro-OMeTAD-based HTL with different weight ratios. At an optimal weight ratio of UCNCs, the PSCs based on the upconverting transport hole layer achieved an average power conversion efficiency of 18.34% under AM1.5G illumination, an increase over 25% compared with conventional HTL based PSCs (14.69%). We systematically explore the optical and electrical enhancement effects of Li(Gd,Y)F4:Yb,Er UCNCs via UV–visible absorption, diffused reflectance, external quantum efficiency (EQE), steady-state and time-resolved photoluminescence, photocurrent property and the space-charge-limited-current (SCLC) measurements. It was found that with the addition of the octahedral UCNCs in a proper proportion the composite HTL exhibits high charge carrier mobility and charge carrier transfer/collection capability. Besides, the embedded UCNCs boost the light harvesting of the PSCs over a large range of wavelengths from 400 nm to 800 nm. Furthermore, with a 980 nm near-infrared (NIR) laser irradiation, the embedded UCNCs acted as efficient upconverting centers to up-convert the NIR light for promisingly expanding the effective absorption spectrum for PSCs.

6,7-Di(thiophen-2-yl)naphtho[2,3-c][1,2,5]thiadiazole and 4,6,7,9-tetra (thiophen-2-yl)naphtho[2,3-c][1,2,5]thiadiazole as new acceptor units for D-A type co-polymer for polymer solar cells

This work emphasizes on the synthesis of two new acceptor units for donor (D)-acceptor (A)-based polymers used in photovoltaic devices, namely NT-Th and Th-NT-Th. Both the NT-based acceptors have been designed using 5,6-positions of benzothiadiazole (BT) and synthesized by Wittig coupling reaction. Newly synthesized acceptor units distinguishes itself from existing literature of naphtho[2,3-c][1,2,5]thiadiazole (NT) acceptor in having additional two Thiophene (Th) units attached at 6,7 position of NT, imparting into it a unique 2-dimensional (2D) type of conjugated structure. Alternate D-A co-polymer of new NT-based acceptors with commonly used BDT donor was synthesized via Stille coupling, resulting in new conjugated polymers (CPs) namely P(BDT-NTTh) and P(BDT-ThNTTh). Both the CPs were characterized by GPC, UV–vis, 1H-NMR, 13C-NMR, TGA and CV. Dihedral angle for optimized geometry and ICT of newly synthesized NT-based polymers have also been investigated using DFT. Theoretical calculations suggest that incorporating two Th-units, separates the donor and acceptor as in case of P(BDT-ThNTTh) leading to lowering of dihedral angle, with maximum value of 42.9˚ resulting in more planar geometry. PSC performance of synthesized CPs have been examined by fabricating BHJ solar cells with configuration ITO/PEDOT:PSS/Polymer-PC71BM/LiF/Al, which resulted in a PCE of 0.34% and 1.31% with P(BDT-NTTh) and P(BDT-ThNTTh) respectively. Hole-mobility for blend of P(BDT-NTTh) and P(BDT-ThNTTh) with PC71BM were calculated using SCLC (space charge limited current) method by fabricating hole only devices of configuration ITO/PEDOT:PSS/Polymer-PC71BM/Cu and mobility of 2.2 × 10−6 and 1.5 × 10-5 cm2 V-1 s-1 were established respectively. Morphology of active layer of fabricated PSC has been studied with atomic force microscopy (AFM) and is correlated with their performances.

Resistive switching behavior in memristors with TiO2 nanorod arrays of different dimensions

In this work, memristors based on TiO2 nanorod arrays (TNAs) were fabricated using a hydrothermal synthesis method. The memristors had a structure consisting of a TNA sandwiched between gold and fluorine doped tin oxide (FTO) coated glass. Devices were constructed using TNAs containing nanorods of different height, diameter and area ratio, with different oxygen vacancy concentrations. The devices exhibit resistance switching behavior and the current through the devices is related to the oxygen vacancy concentration and the area ratio of TNAs. When the height of nanorods is around 3 μm or less, the devices perform well with a current that is as low as 10−8 A in the high resistance state (HRS) and 10−4 A in the low resistance state (LRS). It is found that the space charge limited current (SCLC) mechanism associated with the oxygen vacancies explains the current-voltage behavior of these devices in this three layer structure. A schematic model is presented to illustrate the changes in oxygen vacancy concentration and switching processes, including the formation of new oxygen vacancies (triggered vacancies) to explain the large increase in current at the end of the setting process in these devices.

Graphene nanoflakes and carbon nanotubes on porous silicon layers by spin coating, for possible applications in optoelectronics

Structures of c-Si/PS/GNF/Au and c-Si/PS/CNT/Au have been developed through a simple and inexpensive fabrication method. Porous silicon (PS) layers with nanometer pore sizes have been created by the electrochemical anodization method, which is simple, low-cost, and efficient. Then, graphene nanoflakes (GNF) and carbon nanotubes (CNT) have been deposited by the spin coating method on the porous silicon. PS/GNF and PS/CNT structures showed a considerable reduction in the luminescence of porous silicon which could be attributed by an interaction between porous silicon and carbon nanotubes or graphene nanoflakes. Moreover, SEM images revealed the distribution of these carbon materials on the porous silicon, even different agglomerations could be appreciated both CNT and GNF. Electrical characterization showed rectifying and ohmic behavior with some anomalies that can be related to these carbon structures. Furthermore, it was possible to fit a transport mechanism that resulted to be Space charge Limit Current (SCLC), due to different simulations carried out in this study.

Mechanism and enhancement of the near-threshold low OFF-state breakdown voltage in gallium nitride high electron mobility transistors

We studied AlGaN/GaN high electron mobility transistors grown on a SiC substrate. They had a hard breakdown voltage VBR ≥ 70 V under a deep OFF-state with a much less and softer VBR ∼ 27 V for near-threshold OFF-state gate bias conditions. We established that the low, soft breakdown is due to space charge limited current (SCLC) from drain to source via the GaN buffer, which has deep traps. Previous works had established the presence of SCLC from bulk to gate and drain to gate. For the first time we establish drain to source SCLC. We achieved this by analyzing the IDS–VDS data extracted from the measured IS–VDS. We determined the following by numerical simulation: (a) the density and energy level of traps causing the observed SCLC; (b) the minimum trap density required to suppress the SCLC and raise the VBR up to the avalanche limit for the whole OFF-state regime for devices with a channel length down to 0.15 μm.

Conduction mechanisms of TaN/HfOx/Ni memristors

The conduction mechanisms of TaN/HfOx/Ni memristors are investigated in the wide temperature range from 4.2 to 400 K. The hafnium oxide layer was deposited by ion-beam sputtering deposition (IBSD) at different partial oxygen pressures for various samples, for which resistive switching was possible. This range of partial oxygen pressures corresponded to the x range from 1.78 to 1.81 The analysis and fitting of the current-voltage (I−V) curves of low- and high-resistance states (LRS and HRS, respectively) at different temperatures revealed that, at temperatures above ∼70 K, the conduction is governed by the thermal generation of free carriers and space-charge-limited current (SCLC). Specifically, it is shown that trap-free and trap-mediated SCLCs govern the conduction for the LRS and HRS, respectively. At lower temperatures, the conduction in both states was found to be practically temperature-independent. At the same time, the TaN/HfOx/Ni memristor functioned properly at temperatures as low as 4.2 K. The x value is shown to influence the slope of the HRS I−V curves, and it correlates with the change in the SCLC power-law exponent (m, I ∝ Vm). TaN/HfOx/Ni memristors with low values of x ≤ 1.79 demonstrated the current power-law dependence on voltage in the HRS with m > 2 (3.0–6.5) and for the memristors with higher x values in the HRS of m ≈ 2. Within the suggested model, a local trap-rich conducting region was presumed to be formed in the oxide layer between the metal electrodes after the memristor forming process. The I−V curves modeling indicates that the LRS and HRS differ from each other by the thickness of this active region and the trap distribution. The role of oxygen vacancies and polyvacancies in HfOx, which are considered to act as charge carrier traps, is discussed.

Improved charge transport in PANI:PSS by the uniform dispersion of silver nanoparticles

In the present work, polyaniline:poly (4-styrenesulfonic acid) (PANI:PSS) and silver (Ag) nanoparticle–incorporated PANI:PSS (4-styrenesulfonic acid) are synthesized through a chemical route. The synthesized materials are characterized via X-ray diffractogram (XRD), ultraviolet–visible (UV–Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). The thermal stability of the samples is realized via thermogravimetric analysis (TGA) study. To gain detailed information about the electrical charge transport properties of the synthesized samples, the temperature-dependent current density (J) and voltage (V) data of the samples within a vast temperature range (143 K–303 K) are recorded. The deep analysis of those data reveals that the electrical charge transport mechanism within PANI:PSS and its composites with Ag nanoparticles is governed by a trap-dependent space-charge-limited current (SCLC) mechanism. The evaluated field-dependent mobility data at different temperatures show that silver nanoparticle incorporation within the PANI:PSS matrices below the percolation threshold enhances charge carrier mobility by reducing the trap density. From the analysis of the electrical data, various parameters associated with the charge transport mechanism are estimated, including disorder parameters, the density of states, the optimal hopping distance, and localization lengths. All the parameters estimated from the detailed analysis indicate that a small amount of silver nanoparticle dispersion within a PANI:PSS matrix enhances the overall semiconducting nature of PANI:PSS.

Giant, Anomalous Piezoimpedance in Silicon-on-insulator

A giant, anomalous piezo-response of fully-depleted silicon-on-insulator (FD-SOI) devices under mechanical stress is demonstrated using impedance spectroscopy. This piezo-response strongly depends on the measurement frequency, $\omega$, and consists of both a piezoresistance (PZR) and piezocapacitance whose maximum values are $\pi_R = -1100 \times 10^{-11}$ Pa$^{-1}$ and $\pi_C = -900 \times 10^{-11}$ Pa$^{-1}$ respectively. These values should be compared with the usual bulk PZR in p-type silicon, $\pi_R= 70 \times 10^{-11}$ Pa$^{-1}$. The observations are well described using models of space charge limited electron and hole currents in the presence of fast electronic traps having stress-dependent capture ($\omega_c$) and emission rates. Under steady-state conditions (i.e. when $\omega \ll \omega_c$) where the impedance spectroscopy measurements yield results that are directly comparable with previously published reports of PZR in depleted, silicon nano-objects, the overall piezo-response is just the usual, bulk silicon PZR. Anomalous PZR is observed only under non-steady-state conditions when $\omega \approx \omega_c$, with a symmetry suggesting that the electro-mechanically active fast traps are native Pb$_0$ interface defects. The observations suggest new functionalities for FD-SOI, and shed light on the debate over the PZR of carrier depleted nano-silicon.

Influence of Low-Temperature Annealing on the Electrical Conductivity of SiOx Films

In this paper, the results on the conductivity of silicon enriched SiOx films and the influence of low temperature annealing at 450 °C in the H2 and vacuum are presented. SiOx films were prepared on Si substrate by low pressure chemical vapor deposition (LP CVD) with using SiH4, N2O as the precursor gases and H2 as a carrier gas. The measurements of current-voltage characteristics were carried out in the wide temperature range 95-334 K. It was revealed that the influence of atmosphere of the low temperature annealing is significant. In general case it was established that after the annealing of the initial film in the hydrogen the conductivity increases and after annealing in the vacuum decreases. Characteristic feature of all films (without and with annealing) is the conductivity according to the Mott’s law at low voltages (U < 1 V) in temperature range 295 < T < 345 K. The calculated densities of electron states (traps) in bandgap near the Fermi level from slope of curves in Mott’s coordinate are equal to N = 2.12 × 1017 eV−1 × cm−3 (initial film), N = 4.14 × 1019 eV−1 × cm−3, (H2), N = 6.62 × 1016 eV−1 × cm−3 (vacuum). At higher voltages and lower temperature another transport mechanisms have been revealed. Among them are space-charge limited current (SCLC), Poole-Frenkel mechanism and Fowler-Nordheim tunneling.

One-dimensional π-d conjugated coordination polymers: synthesis and their improved memory performance

Multilevel resistance random access memories (RRAMs) are intensively studied due to their potential applications in high density information storage. However, the low ternary device yields and high threshold voltages based on current materials cannot meet the requirement for applications. Improvement via material innovation remains desirable and challenging. Herein, five one-dimensional conjugated coordination polymers were synthesized via the reaction between metal ions (Zn2+, Cu2+, Ni2+, Pt2+ and Pd2+) and 2,5-diaminobenzene-1,4-dithiol (DABDT) and fabricated into RRAM devices. The as-fabricated ternary memories have relatively low threshold voltages ( V th1: −1 to −1.4 V, V th2: −1.8 to −2.2 V). Their ternary device yields were improved from 24% to 56%. The first and the second resistance switches are interpreted by the space charge limited current (SCLC) and grain boundary depletion limited current (GBLC) modes, respectively. The Pd-DABDT, which is of planar structure, smaller band gap and better crystallinity than others, shows the best performance among these five polymers. Our work paves a simple and efficient way to optimize the performance of ternary RRAM devices employing one-dimensional hybrid materials.

Photoelectric response of localized states in silica glass

The photoelectric response of pure silica glasses excited by excimer lasers has been studied. The samples were made under various conditions. Photoelectric polarization of samples due to the Dember effect has been registered. The signal was recorded under the conditions of a space charge limited current. The space charge resulting from the capture of electrons and holes creates a static electric field that prevents diffusion of released charge carriers. The current registration in the external circuit stops, despite the continuation of photoexcitation. This effect was used as a fact of measuring the photocurrent in the sample volume instead of the parasitic current that is not associated with the sample. The screen has been chosen to prevent the influence of a spurious signal. It has been found that charge carriers are released when excited in the spectral absorption range of localized states of silica. Based on the Dember effect, the sign of the photoelectric response shows the type of charge carriers - an electron or a hole is mobile. Thus, a sample containing aluminum without alkali ions gives a negative signal, which indicates the diffusion of electrons at 290 K, since aluminum is an effective hole trap. An oxygen-deficient sample at 290 K provides a positive signal indicating the diffusion of holes, because the center of oxygen deficiency is an effective electron trap. This sample at 100 K provides a negative signal due to the effective self-trapping of holes.

Fabrication and characterization of La doped PbI2 nanostructured thin films for opto-electronic applications

Herein, we report a facile, cost-effective, solution processed fabrication method for pure and lanthanum (La3+) doped lead iodide (PbI2) thin films and investigated structural, optical, dielectric and electrical properties. Synthesis of PbI2 was confirmed by X-ray diffraction (XRD) and FT-Raman spectroscopy analyses. The fabricated films were grown along (001) plane, with crystallite size in the range of 12–14 nm and observed that crystallinity increases and defects decreases with the increase of La doping concentration. The morphology of fabricated films was observed to be spherical nanoparticles assembled nanosheets, distributed uniformly throughout the films. Moreover, homogeneous La doping in PbI2 was seen via EDX elemental mapping image. Optical band gap was calculated from Ultra violet–visible–near infrared (UV–Vis–NIR) spectra. The band gap of pure PbI2 film was noticed ∼2.44 eV which increase to 2.63 eV for 3% La3+ doped film. Absorption index, refractive index and dielectric constant values were calculated from optical data and found to be strongly dependent on incident photon energy and all parameters show higher values for La doped PbI2 films. I-V characteristics of pure and La-doped PbI2 thin films were carried out in the device configuration viz. FTO/PbI2 (or La-doped PbI2)/Au at room temperature. I-V curve for the pure PbI2 films shows the ohmic behavior while La doped PbI2 films shows non ohmic behavior attributed to space charge limited current. The electrical resistivity values for pure PbI2 film is found to be very high about 1.8 × 1011 Ω-cm.

A conjugated polymer based on alkylthio-substituted benzo[1,2-c:4,5-c’]dithiophene-4,8-dione acceptor for polymer solar cells

In this work, the 2,5-di(alkyl)thiophene unit was replaced with a 2,5-di(alkylthio)thiophene moiety on benzo [1,2-c:4,5-c’]dithiophene-4,8-dione (BDD) unit. The di(alkylthio) substituted BDD was used to obtain a novel copolymer PSBDB-T via Stille polymerization. PSBDB-T shows good solubility and excellent thermal stability. The opto-electronic properties of PSBDB-T were investigated. PSBDB-T has a broad absorption range from 300 nm to 700 nm and deep highest occupied molecular orbital (HOMO) level due to the alkylthio units, which can improve the open-circuit voltage. A solar cell based on PSBDB-T as donor and a near infrared absorbing non-fullerene acceptor achieves a power conversion efficiency (PCE) of 5.0%, which is lower than its analogous polymer PBDB-T with a PCE of 8.8%. The studies of organic field-effect transistors and space charge limited current (SCLC) measurement indicate that PSBDB-T shows a significantly low hole mobility, which is responsible for the low photocurrent and fill factor in solar cells.