Poor Photovoltaic Performance Research Articles

Revealing the full potential of CsPbIBr2 perovskite solar cells: advancements towards enhanced performance.

Cesium lead iodide bromide (CsPbIBr2) perovskite solar cells (PSCs) have improved stability compared to other perovskite compositions. However, they still face significant challenges due to their poor photovoltaic performance parameters, which limit the devices' power conversion efficiencies (PCEs). This study proposes a novel device design to tailor the potential of CsPbIBr2 PSCs by improving their optoelectronic properties. An advanced 3D multiphysics approach was rigorously used to investigate the optics and electrical properties of the proposed CsPbIBr2 PSCs. This approach combines finite-difference time-domain (FDTD) and finite element method (FEM) techniques with the particle swarm optimization (PSO) algorithm. The outcome from the adapted numerical approach is in good agreement with the experimental results. The optimized CsPbIBr2 PSC demonstrates a promising power conversion efficiency (PCE) of over 16.4%, associated VOC of 1.53 V, FF of 80.6%, and JSC of 13.4 mA cm-2. Therefore, the potential of CsPbIBr2 perovskites could be further explored with continued research and development in material science and device physics.

Phenoxy Group-Containing Asymmetric Non-Fullerene Acceptors Achieved Higher VOC over 1.0 V through Alkoxy Side-Chain Engineering for Organic Solar Cells.

Alkoxy side chain engineering on the β-position of the thienothiophene units of Y6 derivatives plays a vital role in improving photovoltaic performances with simultaneously increasing open-circuit voltage (Voc) and fill factor (FF). In this work, we prepared a series of asymmetric non-fullerene acceptors (NFAs) by introducing alkoxy side chains and phenoxy groups on the state-of-the-art Y6-derivative BTP-BO-4F. For the comparison, 2O-BO-4F with a symmetric alkoxy side chain on the outer thiophene units and BTP-PBO-4F with an asymmetric N-attached phenoxy alkyl chain on the pyrrole ring are synthesized from BTP-BO-4F. Thereafter, we construct four asymmetric NFAs by introducing different lengths of linear/branched alkoxy chains on the β-position of the thienothiophene units of BTP-PBO-4F. The resulting NFAs, named L10-PBO, L12-PBO, B12-PBO, and B16-PBO (L = linear and B = branched alkoxy side chains), are collectively called OR-PBO-series. Unexpectedly, all OR-PBO NFAs exhibit strong edge-on molecular packing and weaker π-π interactions in the film state, which diminish the charge transfer in organic solar cell (OSC) devices. As a consequence, the optimal devices of OR-PBO-based binary blends show poor photovoltaic performances [power conversion efficiency (PCE) = 6.52-9.62%] in comparison with 2O-BO-4F (PCE = 12.42%) and BTP-PBO-4F (PCE = 15.30%) reference blends. Nevertheless, the OR-PBO-based binary devices show a higher Voc and smaller Vloss. Especially, B12-PBO- and B16-PBO-based devices achieve Voc over 1.00 V, which is the highest value of Y-series OSC devices to the best of our knowledge. Therefore, by utilizing higher Voc of OR-PBO binary blends, B12-PBO and B16-PBO are incorporated into the PM6:BTP-PBO-4F-based binary blend and fabricated ternary devices. As a result, the PM6:BTP-PBO-4F:B12-PBO ternary device delivers the best PCE of 15.60% with an increasing Voc and FF concurrently.

Sol-Gel Prepared Spinel HTLs for Assembling 20% Efficiency Perovskite Solar Cell in Air Without Using Anti-Solvent and Toxic Solvent.

Low-temperature sol-gel prepared ZnCo2 O4 spinel-based thin films are developed as high-performance hole transporting layer (HTL) for coating perovskite film (NA-Psk) from the basic MAPbI3 /ACN/CH3 NH2 solution in air without using anti-solvent. Inverted PSC based on 2mole% (vs Zn) Cu2+ doped ZnCo2 O4 (2%Cu@ZnCo2 O4 ) HTL and NA-Psk absorber exhibit the maximum power conversion efficiency (PCE) of 20.0% with no current hysteresis while the cell based on ZnCo2 O4 and PEDOT:PSS HTL (using NA-Psk absorber) achieves the PCE of 15.79% and 12.3% with a current hysteresis index of 9.8% and 32.4%, respectively. Without encapsulation, PSCs based on 2%Cu@ZnCo2 O4 , ZnCo2 O4 , and PEDOT:PSS HTLs maintain 90%, 77%, and 12%, respectively of the original efficiency by standing in ambient atmosphere (temperature: 20-25°C, RH:30%-40%) for 1800h. Large area (10cm× 10cm substrate) perovskite mini-module (PSM) with PCE over 15% is also demonstrated by using sol-gel prepared 2%Cu@ZnCo2 O4 HTL. The poor photovoltaic performance of PEDOT:PSS HTL is due to the basic MAPbI3 /ACN/CH3 NH2 solution will deprotonate the acidic PEDOT:PSS to reduce its conductivity whereas ZnCo2 O4 HTL are not affected by basic perovskite precursor solution.

Novel Squaraine dyes for high-performance in dye-sensitized solar cells: Photophysical properties and adsorption behavior on TiO2 with different anchoring groups

The utilization of near-infrared (NIR) photons holds paramount importance in the realm of electricity conversion, as it offers a promising avenue to enhance the capabilities of dye-sensitized solar cells (DSSCs). In light of this, a pioneering effort was made to synthesize two novel Squaraine (SQI-5 and SQI-6) dyes that comprise two functional groups (-SO3H and -COOH) with the aim of producing efficient far-red sensitizers that could be applied in DSSCs. The efficacy of the recently developed dyes was extensively evaluated using diverse analytical techniques, which confirmed their exceptional solubility in multiple organic solvents. Investigation into the adsorption behavior of the SQI-5 and SQI-6 sensitizers on mesoporous TiO2 showed that the -COOH anchoring group demonstrated a higher rate of adsorption compared to the -SO3H group, whereas the stability of the adsorbed dyes was superior for -COOH as opposed to -SO3H following dye desorption tests. Both theoretical and experimental methods were employed to evaluate the impact of the anchoring groups on the energy levels of the HOMO- LUMO. Despite having a high binding strength, favorable energy cascade, and decreased dye loading, the SQI-5 sensitizers featuring a sulfonic acid anchoring group demonstrated poor photovoltaic performance in comparison to SQI-6, which featured -COOH anchoring group and recorded the best photovoltaic performance compared to SQI-5 sensitizer investigated. SQI-6 achieved a power conversion efficiency (PCE) of 4.21% after simulating solar irradiation, as evidenced by its short-circuit current density (Jsc), open circuit voltage (Voc), and fill factor(FF) of 14.2 mA/cm2, 0.69 V, and 0.45, respectively. This advancement represents a significant step forward for DSSCs and paves the way for a more efficient future of DSSCs in the near-infrared (NIR) region.

A direct correlation between structural and morphological defects of TiO2 thin films on FTO substrates and photovoltaic performance of planar perovskite solar cells

Titanium oxide (TiO2) precursor is often deposited on conductive fluorine doped tin oxide (FTO) to convert into crystalline anatase phase after a thermal annealing at 400–550 °C. A higher annealing temperature can increase the crystallinity of TiO2, but it may also induce morphological changes in both TiO2 and FTO. In this work, structural and morphological changes in thermally annealed FTO and TiO2/FTO are identified and semi-quantified by X-ray diffraction, scanning electron and atomic force microscopies. 400 °C annealed TiO2 shows the lowest crystallinity and the highest dislocation density, giving a poor photovoltaic performance of planar perovskite solar cells (p-PSCs). 550 °C annealed TiO2 exhibits the highest crystallinity and lowest dislocation density, but at such temperature the FTO films undergo an increase of surface roughness by more than 25%. As a result, 550 °C annealed TiO2 coatings on FTO substrates show the highest concentration of surface fracture and a larger exposed area of FTO, permitting a direct contact of upcoming perovskite with the FTO substrate. TiO2 thin films annealed at 450 or 500 °C show a compromising between the crystalline structure and defect density, giving a better energy conversion efficiency of 16.3% of p-PSCs prepared under ambient conditions.

Fast Recombination of Charge-Transfer State in Organic Photovoltaic Composite of P3HT and Semiconducting Carbon Nanotubes Is the Reason for Its Poor Photovoltaic Performance

Although the photovoltaic performance of the composite of poly-3-hexylthiophene (P3HT) with semiconducting single-walled carbon nanotubes (s-SWCNT) is promising, the short-circuit current density jSC is much lower than that for typical polymer/fullerene composites. Out-of-phase electron spin echo (ESE) technique with laser excitation of the P3HT/s-SWCNT composite was used to clarify the origin of the poor photogeneration of free charges. The appearance of out-of-phase ESE signal is a solid proof that the charge-transfer state of P3HT+/s-SWCNT- is formed upon photoexcitation and the electron spins of P3HT+ and s-SWCNT- are correlated. No out-of-phase ESE signal was detected in the same experiment with pristine P3HT film. The out-of-phase ESE envelope modulation trace for P3HT/s-SWCNT composite was close to that for the polymer/fullerene photovoltaic composite PCDTBT/PC70BM, which implies a similar distance of initial charge separation in the range 2-4 nm. However, out-of-phase ESE signal decay with delay after laser flash increase for P3HT/s-SWCNT composite was much faster, with a characteristic time of 10 µs at 30 K. This points to the higher geminate recombination rate for the P3HT/s-SWCNT composite, which may be one of the reasons for the relatively poor photovoltaic performance of this system.

Advances in the research of carbon electrodes for perovskite solar cells.

Perovskite solar cells (PSCs) were first proposed in 2009. They have the advantages of low cost, a simple manufacturing process and excellent photoelectric performance. PSC electrodes are mainly made from precious metals such as gold and silver. Still, the cost of precious metals is high and they react with the other components of the PSCs, resulting in the poor stability of the photovoltaic device. Using carbon as an electrode material can both reduce the cost and significantly improve the stability of the photovoltaic device. However, the poor interface contact between the carbon electrode and perovskite and carbon electrode resistance results in poor photovoltaic device photoelectric performance. Finding a way to successfully utilize carbon as an alternative electrode material is a key step toward moving PSCs from the laboratory to industrialization. This paper reviews the application of carbon black, graphite, graphene, carbon nanotubes (CNTs) and composite carbon electrode in PSCs, focusing on progress in the research of doping, structure, interface modification and the production process.

Hierarchically Assembled Counter Electrode for Fiber Solar Cell Showing Record Power Conversion Efficiency

AbstractFiber solar cells have attracted significant interest as a promising wearable power supply solution for their merits of high flexibility, lightweight, and good compatibility with textile configuration and weaving process. However, because of the limited ion diffusion and charge transfer in the fiber counter electrode, the poor photovoltaic performances have long been one obstacle to hinder their real applications. Herein, in mimicking the efficient mass transport and exchange through the vascular tissue of plants like pine needle, a hierarchically assembled carbon nanotube (HCNT) fiber counter electrode is fabricated by a scalable process. The designed hierarchically aligned channels with large sizes of micrometers and small sizes of tens of nanometers in the HCNT fiber offers high‐flux pathways for rapid ion diffusion and abundant active area for charge transport, thus endowing the fiber dye‐sensitized solar cell with a record power conversion efficiency of 11.94%. By weaving such fiber solar cells in a scalable way, a flexible and breathable large photovoltaic textile (17 cm × 22 cm) is made to present a power output of 22.7 mW. These fiber solar cells are further integrated with fiber lithium‐ion batteries to efficiently power wearable electronics.

PBDB-T-Based Binary-OSCs Achieving over 15.83% Efficiency via End-Group Functionalization and Alkyl-Chain Engineering of Quinoxaline-Containing Non-Fullerene Acceptors.

Molecular backbone modification, alkyl-chain engineering, and end-group functionalization are promising strategies for developing efficient high-performance non-fullerene acceptors (NFAs). Herein, two new NFAs, named TPQ-eC7-4F and TPQ-eC7-4Cl, are designed and synthesized. Both molecules have linear octyl chains on fused quinoxaline-containing heterocyclics as the central backbone and difluorinated (2F)/dichlorinated (2Cl) 1,1-dicyanomethylene-3-indanone (IC) as the end-group units. The influences of alkyl-chains on fused quinoxaline backbone and different halogenated end-groups on optical, electrochemical, and photovoltaic performances of organic solar cells (OSCs) are studied. In comparison with TPQ-eC7-4Cl, TPQ-eC7-4F exhibits blue-shifted absorptions with higher molar extinction coefficients in the film state as well as in the donor/acceptor (D/A) blend film state and up-shifting lowest unoccupied molecular orbital (LUMO) energy level. As a result, the OSC devices based on the PBDB-T:TPQ-eC7-4F display an outstanding power conversion efficiency (PCE) of 15.83% with a simultaneously increased open-circuit voltage (Voc) of 0.85 V, a short-circuit current-density (Jsc) of 25.89 mA cm-2, and a fill factor (FF) of 72.20%, whereas the PBDB-T:TPQ-eC7-4Cl-based OSC device shows a decent PCE of 14.48% with a Voc of 0.84 V, a Jsc of 24.56 mA/cm2, and an FF of 69.77%. To the best of our knowledge, this is the highest photovoltaic performance of PBDB-T-based single-junction binary-OSCs. In comparison, ascribed to the high crystallinity and low solubility of BTP-eC7-4Cl, the corresponding PBDB-T:BTP-eC7-4Cl-based OSC device shows poor photovoltaic performance (PCE of 11.87%). The experimental results demonstrate that fine-tuning the fused quinoxaline backbone with alkyl-chain and end-group functionalization are promising strategies to construct high-performance NFAs for PBDB-T-based single-junction binary-OSCs.

Overcoming the poor performance of n-CdS/p-SnS solar cells by plasmonic effect of gold and silver nanoparticles

It is known that one of the biggest problems in CdS/SnS solar cells is the efficiency deterioration, which hinders their wider use in application fields. Consequently, in this research, we manipulated the poor photovoltaic performance of CdS/SnS solar cells by the plasmonic effect of silver and gold nanoparticles of particle size of about 7.1 ± 1.4 nm, and 10.01 ± 2.2 nm, respectively. The structural and morphological properties of each layer of the CdS/SnS heterojunction are inspected individually and in a bilayer form with and without nanoparticles (NPs) decoration. The EDAX analysis and surface roughness analysis are evaluated in detail. Furthermore, the measured optical absorption and reflection profile witnessed significant enhancements where the absorption is increased by 235.9% and 835.6% at 550 nm by Au-NPs and Ag-NPs decoration, respectively. The electrical characteristics of the engineered CdS/SnS heterojunction are tested under dark and different irradiances (20−100) mW/cm2. The decoration by the plasmonic nanoparticles induced marvelous improvements in the Voc and Jsc values. Excitingly, the Au-NPs improved the poor efficiency of the virgin CdS/SnS solar cell from (0.022–0.066) % by one order of magnitude to be in the range (0.436–0.51) %, while Ag-NPs decorated cell achieved efficiency in the range (2.507–4.363) %. This new record in CdS/SnS efficiencies is explained in terms of the heterojunction type transformation using the calculated band offsets depending on the resulted values of valance band maximum of CdS and SnS and the energy difference of core levels in the heterojunction form using the photoelectron spectroscopy results.

Theoretical investigation on two‐dimensional monofluorinated phenylethylammonium perovskite

AbstractMore and more two‐dimensional (2D) perovskites are synthesized and used in solar cells. Theoretical investigations on their structural and electronic properties can explore the origin of crystal structural and optoelectronic differences caused by organic spacers. Here, formation energy, non‐covalent interaction, band structure, exciton binding energy, carrier mobility, and optical absorption spectra of 2D monofluorinated phenylethylammonium lead iodide perovskite were calculated using density functional theory. Results show that steric effect leads to the orientational disorder of spacers in ortho‐fluorinating phenylethylammonium perovskite, which further lead to a poor photovoltaic performance and weak interaction leads to the herringbone configuration of spacers in meta‐fluorinating phenylethylammonium perovskite. Exciton binding energy significantly influences the short circuit current density (JSC) which can well explain the experimental trends of JSC. This research shows that para‐fluorinating is the best choice and the important of weak interactions and inductive effect, providing a guideline for new spacer designing.

Growth of MoS2 and metal back electrode-dependent performance of MoS2/Si heterojunction solar cells

In this work, MoS2 thin films were successfully synthesized by chemical vapor deposition (CVD) using MoO3 and sulfur powders as precursor sources. The effect of the MoO3 dosage and heating temperature on the quality of the synthesized MoS2 films are investigated and a detailed reaction mechanism is proposed to interpret the obtained experimental result. Furthermore, we have studied the influence of different metal back electrodes (including Ag and Au) on the photovoltaic performance of the fabricated MoS2/Si heterojunction solar cell. It is shown that, in comparison with the solar cell using Au as a metal back electrode, the solar cell using Ag as a metal back electrode has poor photovoltaic performance with the appearance of the S-type shape in the measured current density-voltage curve. Finally, numerical simulation based on AFORS-HET software has been carried out to investigate the photovoltaic performance of the [Formula: see text]-MoS2/[Formula: see text]-Si heterojunction solar cell under different work functions of the metal back electrode. The result of numerical simulation is consistent with our experiential result in the trend. This work is highly relevant to the development of transition metal dichalcogenides in the application of solar cells.

Evaluation of the potential of nanofluids containing different Ag nanoparticle size distributions for enhanced solar energy conversion in hybrid photovoltaic-thermal (PVT) applications

Hybridising photovoltaic and photothermal technologies into a single system that can simultaneously deliver heat and power represents one of the leading strategies for generating clean energy at more affordable prices. In a hybrid photovoltaic-thermal (PVT) system, the capability to modulate the thermal and electrical power output is significantly influenced by the spectral properties of the heat transfer fluid utilised. In this study, we report on one of the first experimental evaluations of the capability of a multimodal silver nanofluid containing various particle shapes and particle sizes to selectively modulate the solar energy for PVT applications. The diverse set of particle properties led up to a 50.4% enhancement in the solar energy absorbed by the nanofluid over the 300 nm—550 nm spectral region, where silicon is known to exhibit poor photovoltaic conversion performances. This improved substantially the absorption of solar energy, with an additional 18–129 W m−2 of thermal power being generated by the PVT system. Along with the advancements made in the thermal power output of the PVT system, a decrease of 4.7–36.6 W m−2 in the electrical power generated by the photovoltaic element was noted. Thus, for every ∼11 W m−2 increase of thermal power achieved through the addition of the nanoparticles, a reduction of ∼3 W m−2 in the ability to generate clean electricity was sustained by the PVT. Despite the energy trade-offs involved under the conditions of the nanofluid, the PVT system cumulatively harvested 405 W m−2 of solar energy, which amounts to a total conversion efficiency of 45%. Furthermore, the economics of the additional energy harvested through merging of the two systems was found to reach an enhancement of 77% under certain European conditions.

Numerical analysis and design of high performance HTL-free antimony sulfide solar cells by SCAPS-1D

Among the various absorbers encountered in thin film solar cells (TFSCs), antimony sulfide (Sb2S3) is considered a suitable candidate as it is a non-toxic and earth-abundant besides its high absorption coefficient. However, some critical issues cause its poor photovoltaic performance. These include unoptimized Sb2S3 layer, interface recombination and cell properties like the ineffective carrier collection and transport. To enhance the power conversion efficiency (PCE) of Sb2S3 solar cell, we suggest some design guidelines by employing device simulation. First, a calibration step is performed vs an experimental arrangement consists of FTO/TiO2/Sb2S3/Spiro-OMeTAD/Au to validate the simulation model. Next, as the organic hole transport material (HTM) often has poor long-term operation stability and demands high-cost fabrication processes, an HTL-free cell is proposed and designed by investigating the impact of the main technological and physical parameters. In the first step in the design of the HTL-free cell, we provide an affinity engineering methodology to tune the conduction band offset between the electron transport layer (ETL) and the absorber. Based on this approach, the most appropriate electron transport material (ETM) is chosen that fulfills the maximum efficiency. Then, an optimization routine is performed to select the most appropriate design parameters and the PCE of the optimized case is found to be about 22%. All simulations, carried out in this work, are performed by SCAPS-1D device simulator under AM1.5G illumination and 300 K temperature.

Enhancing efficiency and stability of inverted structure perovskite solar cells with fullerene C60 doped PC61BM electron transport layer

[6, 6]-phenyl C61butyric acid methyl ester (PC61BM) is a common fullerene derivative widely employed as an electron transport layer in inverted perovskite solar cells. However, major challenges such as interfacial recombination, current leakage and low mobility results in poor photovoltaic performance and stability for PC61BM-based devices. To overcome these issues, we demonstrated, for the first time, doping of the PC61BM with fullerene C60 to tailor the properties of the PC61BM. This doping approach helped to realize superior power conversion efficiency of perovskite solar cell with 17.46% versus pristine device with 14.20%. The C60 doped PC61BM reinforced the surface morphology of the PC61BM layer with reduced roughness and better coverage, up-shift of Fermi Level, higher electrical conductivity, higher maximum charge carrier generation rate, and higher charge collection probability. All these improvements contributed to reduced charge leakage at the interface, reduced charge recombination and promoted efficient charge transfer, transport, and collection. Furthermore, the enhanced hydrophobicity of the C60 doped PC61BM enabled superior ambient device stability compared to the pristine device. This work facilitates a simple and effective route to tailor perovskite solar cell performance towards higher efficiency and better stability.

Surface modification of CuS counter electrodes by hydrohalic acid treatment for improving interfacial charge transfer in quantum-dot-sensitized solar cells

High charge transfer resistance and low electrocatalytic activity of counter electrodes (CEs) are mainly responsible for the poor photovoltaic performance of quantum-dot-sensitized solar cells (QDSSCs). Herein, a novel strategy has been successfully introduced for the first time to improve the electrocatalytic activity and charge transfer properties of a copper sulfide (CuS) CE by modifying it with the addition of hydrohalic acids (HHA). Through the suitable surface modification of HHA-incorporated CuS CE, the charge transfer from the external circuit to the CE surface was effectively facilitated. The electrochemical analyses suggest that charge transfer resistance is sufficiently reduced at the CE/electrolyte interface by using the HHA-treated CuS CEs. This improvement is mainly attributed to the high electrocatalytic activity of the modified CEs for the reduction of the polysulfide redox couple electrolyte in QDSSCs. The device constructed with TiO2/CdS/CdSe/ZnS photoanodes and the hydrogen-fluoride-treated CuS (HFCuS) CE exhibits a power conversion efficiency of 4.25%, which is considerably higher than that of the device with the bare CuS CE (3.11%). These findings can facilitate the fabrication of highly efficient CEs for next-generation solar cells.

Ionic Liquid-Induced Ostwald Ripening Effect for Efficient and Stable Tin-Based Perovskite Solar Cells.

Tin-based perovskite solar cells (PVSCs) are regarded as the most promising alternative among lead-free PVSCs. However, the rapid crystallization for tin-based perovskite tends to cause inferior film morphology and abundant defect states, which make poor photovoltaic performance. Here, 1-butyl-3-methylimidazolium bromide (BMIBr) ionic liquids (ILs) with strong polarity and a low melting point are first employed to produce the Ostwald ripening effect and obtain high-quality tin-based perovskite films with a large grain size. Meanwhile, the non-radiative recombination ascribed from defect states can also be effectively reduced for BMIBr-treated perovskite films. Consequently, a photoelectric conversion efficiency (PCE) of 10.09% for inverted tin-based PVSCs is attained by the Ostwald ripening effect. Moreover, the unencapsulated devices with BMIBr retain near 85% of the original PCE in a N2 glovebox beyond 1200 h and about 40% of the original PCE after exposure to air for 48 h.

Side-chain engineering of copolymers based on benzotriazole (BTA) and dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophenes (DTBDT) enables a high PCE of 14.6%

Dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophenes (DTBDT) is a kind of prospective candidate for constructing donor-π-acceptor (D-π-A) copolymer donors applied in organic solar cells but is restricted due to its relatively poor photovoltaic performance compared with benzo[1,2-b;4,5-b′]dithiophenes (BDT)-based analog. Herein, three conjugated polymers (PE51, PE52 and PE53)-based DTBDT and benzo[d][1,2,3]triazole (BTA) bearing different lengths of alkyl side chain were designed and synthesized. The change in alkyl chain length can obviously affect the energy level distribution, molecular stacking, miscibility and morphology with the non-fullerene acceptor of Y6. Polymer PE52 with a moderate alkyl chain realized the highest short-current density (J SC) and fill factor (FF) of 25.36 mA cm−2 and 71.94%, respectively. Compared with BDT-based analog J52-Cl, the significantly enhanced crystallinity and intermolecular interaction of PE52 had effectively boosted the charge transport characteristic and optimized the surface morphology, thereby increasing the power conversion efficiency from 12.3% to an impressive 14.6%, which is the highest value among DTBDT-based and BTA-based polymers. Our results show that not only could high efficiency be achieved via using DTBDT as a D unit, but the length of the alkyl chain on BTA has a significant impact on the photovoltaic performance.

Origin of poor photovoltaic performance of bis(tetracyanoantrathiophene) non-fullerene acceptor

Abstract Light-induced EPR and out-of-phase electron spin echo techniques were applied to identify the origin of low photovoltaic performance of novel non-fullerene antrathiophene-based acceptor 2,2′-[2,2′-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(anthra[2,3-b]thiophene-5,10-diylidene)]tetrapropanedinitrile (AT1), compared to conventional fullerene acceptors. These techniques revealed that average trapping energy of electrons in PCDTBT/AT1 blend is higher than that in the blends of PCDTBT with fullerene acceptors, while the distance of the initial photo-induced electron transfer is decreased. These two effects are suggested to enhance the efficiency of geminate recombination in PCDTBT/AT1 blend and reduce the yield of free charges, which is supposed to be the main reason for poor OPV performance of AT1-containing blends. Low electron mobility μe = 3.5 *10-6 cm2V-1s−1 is estimated for AT1 from photo-CELIV experiment. Strong localization of the electrons on terminal acceptor units of AT1 consistently explains both efficient geminate recombination in blends of antrathiophene-based acceptor with polymer donors and low electron mobility in AT1.

Investigation of Cu2ZnSnS4 solar cell buffer layer fabricated via spray pyrolysis

Copper zinc tin sulfide solar cells were fabricated by using spray pyrolysis from a window layer to an absorber layer. ZnS and In2S3 buffer layers were deposited on the TiO2 layer, and the photovoltaic characteristics were investigated. The ZnS buffer demonstrated a poor photovoltaic performance because of its poor surface coverage and micro-cracks at fluorine-doped tin oxide/TiO2 layers. The In2S3 buffer layer sprayed at low temperature (<360 °C) showed a large difference between photo and dark currents beyond the open-circuit voltage (VOC). When the spraying temperature exceeded 390 °C, the devices showed high dark leakage currents at reverse biases because of the high conductivity of the buffer layer, resulting in decreased VOC and short-circuit current density (JSC). The optimum temperature for spraying In2S3 is 360 °C, and the best performing device showed 410 mV, 30.4 mA/cm2, 35.3%, and 4.4% of VOC, JSC, fill factor, and efficiency, respectively.