Decrease In Fill Factor Research Articles

Microstructural Passivation of Patterned Al2O3 Back Contacts on CdS/CdTe Solar Cells

AbstractPatterned aluminum oxide (Al2O3) back contact on cadmium telluride (CdTe) solar cells can effectively mitigate the loss of the majority carriers while retaining the passivation benefits for minority carriers. This study investigates the impact of the point‐contact geometry on cell performance, where the spacing of the microholes is systematically varied at a constant microhole diameter (≈16 µm). Microhole arrays are created on an evaporated Al2O3 layer (≈30 nm) on CdTe using laser‐beam lithography and selective wet etching processes. Comparative analysis indicates a significant decrease in fill factor (FF) and short‐circuit current (ISC) when the contact fraction falls below 30%, likely due to the Al2O3 barrier impeding majority carriers. Above this fraction, FF and ISC are comparable to those of baseline CdTe cells without Al2O3. Open‐circuit voltage (VOC) shows a gradual decrease as Al2O3 coverage is reduced but exhibits a slight increase (<15 mV) when the contact fraction exceeds 30%. Cathodoluminescence (CL) characterization reveals that significantly improved radiative recombination occurs within the CdTe grain bulk with Al2O3, whereas this effect on grain boundaries is minimal. The findings imply complex local carrier dynamics in the patterned back‐contact region, closely tied to the microstructural properties of CdTe‐based solar cells.

Comparative study of cadmium telluride solar cell performance on different TCO‐coated substrates under concentrated light intensities

AbstractConcentrating photovoltaics is an attractive route for achieving high power output with thin film solar cells, using low‐cost optics. In this work, the performance of CdTe:As thin film solar cells on two different transparent conducting oxide (TCO)‐coated substrates is investigated and compared under varying concentrated light intensities (1–6.3 Suns). Samples tested had CdZnS/CdTe:As devices deposited atop of either a soda‐lime glass with a fluorine‐doped tin oxide TCO or an ultra‐thin glass (UTG) with an aluminium zinc oxide TCO and ZnO high‐resistive transparent (HRT) layer. Device current density was found to increase linearly with increased light intensities, for both sample configurations. Power conversion efficiencies of both device samples decreased with increased light intensity, due to a decrease in fill factor. The fill factor, for both sample configurations, was affected by reducing shunt resistance with increasing illumination intensity. The two device types performed differently at the high illumination intensities due to their series resistance. Light‐soaking devices under 6.3 Suns illumination intensity for 90 min showed no significant performance degradation, indicative of relatively stable devices under the highest illumination intensity tested. Efficiency limiting factors are assessed, evaluated and discussed.

Improved performance of kesterite Cu2ZnSn(S,Se)4 thin film solar cells by Ag/Ge co-doping

Cation doping is an important approach to improve the performance of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells. Since different cation dopant has different effects on the defects and crystallization of CZTSSe absorber, it is expected to achieve better device performance via the synergistic effects of double cation co-doping compared with the single cation doping. Herein, we investigated the effects of Ag/Ge co-doping on CZTSSe solar cells by doping Ge in an already optimized Ag-alloyed CZTSSe (ACZTSSe). It is found that incorporating a small amount of Ge can further improve the crystallinity and minority carrier lifetime of ACZTSSe. The low-temperature photoluminescence results reveal that the Ge doping primarily suppressed the SnZn defects in ACZTSSe, thereby further boosting the device performance. However, higher Ge doping concentration can lead to a discontinuous surface morphology, which is believed to be related with the relatively low melting temperature and double-layered structure of ACZTSSe absorber. The deteriorated surface morphology results in photocurrent loss in the near-infrared region and decreased fill factor. As the Ge doping ratio increases, there is a balance between the defects and morphology. A champion power conversion efficiency (PCE), 11.4%, was achieved for the Ag/Ge co-doped CZTSSe solar cells at Ge substitution rate of 3%. Compared with the single Ag doping, the average PCE was further promoted by 0.5% due to Ag/Ge co-doping.

Innovative photovoltaic approach: Cd1-xBexTe mixed semiconductor crystals for novel dye-sensitized solar cells

This paper deals with the synthesis and properties of new ternary mixed Cd1-xBexTe (cadmium beryllium telluride) crystal-based electrodes for photovoltaic cells which is a modified version of dye- sensitized solar cells. We determined the thermal stability and photovoltaic performance of the obtained devices. Cd1-xBexTe crystals are grown using the Bridgman technique at high temperatures and pressure for different compositions. Using the modified doctor blade method, we fabricated dye-sensitized solar cells (DSSC) using Cd1-xBexTe-based film as working electrodes. The mixed crystals with the highest beryllium content (10 %) and the lowest (1 %) are used. At the same time, the counter electrode and polymer electrolytes are common. Comparative studies with standard DSSC are also undertaken to compare the stability and charge mechanism. As prepared, DSSC using ternary Cd1-xBexTe showed efficiency as high as 3.11 % at 1 sun condition. The life span measurement indicated promising results, and DSSC is stable up to 720 h with a reasonable decrease in fill factor from 84 to 55.

Modulation of Charge Transport from Two-Dimensional Perovskites to Industrial Charge Transport Layers by the Organic Spacer-Dependent Exciton-Phonon Interactions.

In the past decade, two-dimensional (2D) perovskite surface treatment has emerged as a promising strategy to improve the performance of three-dimensional (3D) perovskite solar cells (PSCs). However, systematic studies on the impact of organic spacers of 2D perovskites on charge transport in 2D/3D PSCs are still lacking. Here, using 2D perovskite film/C60 heterostructures with different organic spacers [butylamine (BA), phenylethylamine (PEA), and 3-fluorophenethylamine (m-F-PEA)], we systematically investigated the carrier diffusion and interfacial transfer process. Using a 2D perovskite film with a thickness of ∼7 nm, we observed subtle differences in electron transfer time between 2D perovskites and C60 layers, which can be attributed to limited thickness and similar electron coupling strength. However, with the thickness of 2D perovskite increasing, electron transfer efficiency in the (BA)2PbI4/C60 heterostructure exhibits the most rapid decrease due to poor carrier diffusion of (BA)2PbI4 caused by stronger exciton-phonon interactions compared to (PEA)2PbI4 and (m-F-PEA)2PbI4 in thickness-dependent charge transfer research. Meanwhile, the fill factor of 2D/3D PSC treated with BAI exhibits the most rapid decrease compared to PEAI- and m-F-PEAI-treated 2D/3D PSCs with the concentration increase of passivators. This study indicates that it is easier to enhance open-circuit voltages and minimize the decrease of fill factor by increasing the concentration of passivators in 2D/3D PSCs when using passivators with a rigid molecular structure.

Addressing sodium ion-related degradation in SHJ cells by the application of nano-scale barrier layers

Silicon heterojunction (SHJ) solar cells are renowned for their high efficiency. However, SHJ solar cells are susceptible to various contaminants, leading to significant performance degradation when exposed to damp-heat conditions (e.g., 85 °C and 85% relative humidity). Sodium (Na) has been identified as one of the main contributors to degradation in silicon solar modules subjected to damp-heat conditions. This work investigates the role of an ultra-thin AlOx capping layer (∼10 nm) in preventing the failure in SHJ cells caused by Na-related contaminants. NaCl is applied directly to the solar cell, and the unencapsulated cell undergoes a damp heat test at 85 °C and 85% relative humidity (DH85). It is found that without the AlOx barrier layer, the SHJ cells experience a relative reduction in power of ∼30%rel after only 20 h at DH85. Both the front and rear sides of the cell degrade when exposed to NaCl. This is primarily due to a deterioration of the Ag contact resulting in increased series resistance (Rs), and decrease in fill factor (FF), and an increase in recombination, leading to a significant drop in open-circuit voltage (Voc), particularly when NaCl is applied on the rear side. However, when an AlOx barrier layer is applied to the SHJ cells, the performance losses caused by NaCl are significantly reduced to only ∼3.3%rel. The loss in Voc on the rear side is completely suppressed, and there is only a slight increase in Rs of ∼50%rel compared to ∼300%rel increase in Rs for cells without the AlOx barrier layer. These findings indicate that the ultra-thin AlOx barrier layer provides effective protection for SHJ cells against Na ions, mitigating both Rs and recombination losses. This AlOx barrier layer depositing method is compatible with existing industrial mass-production ALD tools and thus presents a viable solution at the cell level for SHJ cells.

Corrosion effects in bifacial crystalline silicon PV modules; interactions between metallization and encapsulation

This study addresses the influence of different encapsulation materials on performance losses in bifacial PV modules after extended damp heat testing. The widely used ethylene vinyl acetate (EVA) is compared to polyolefin elastomers (POE) and thermoplastic polyolefins (TPO). We show that modules based on n-type bifacial solar cells (tunnel oxide passivated contact, TOPCON) are more prone to degradation than p-type (Passivated emitter rear cell, PERC) based laminates. More specifically, the front side metallization of these n-type cells corrodes under extended damp heat testing, yielding a decreased fill factor in the I–V characteristics and the appearance of dark spots and dark areas in electroluminescence imaging. The newer generation of encapsulant materials (POE and TPO), slowly replacing EVA in the modules commercialized today, demonstrate an improved protection of the metallization. Apart from the nature of the encapsulant, the cell type and the presence or absence of glass cover plates are also shown to influence the metal grid corrosion. To better understand the mechanisms at play, post-mortem analysis was carried out on small sized degraded PV laminates, by drilling out circular samples (“coring”) that could be analyzed in depth. The analyses revealed a weakened bond between the metallization and the silicon emitter, ultimately causing metal grid delamination. The proposed mechanism behind this delamination starts with the degradation of lead glass, which is part of the cell metallization grid and contains lead oxide (PbO). This compound is susceptible to dissolution in acidic environment.

Neutron irradiated perovskite films and solar cells on PET substrates

Flexible perovskite solar cells feature high power-per-weight ratio and low cost manufacturing, which make them very attractive for space and avionic applications. It is thus paramount to assess their response to the harsh space environment. Although an increasing number of studies have been investigating the effect of electron and proton radiation on perovskite solar cells, very few have dealt with neutron irradiation and even less with flexible devices. In this paper, the stability of unencapsulated flexible perovskite solar cells against fast neutron irradiation at two different fluence levels is evaluated, comparing commercially available spiro-OMeTAD and an in-house modified P3HT as the hole transport materials. We observed degradation for both materials and at both fluences. Modified-P3HT cells experienced remarkable smaller voltage and current losses compared to spiro-OMeTAD; still, their overall performance degraded similarly to spiro-OMeTAD devices at higher fluence, whilst it suffered a much higher drop than spiro-OMeTAD at lower fluence, as a consequence of a larger decrease in fill factor, ascribable to a sub-optimal perovskite/polymer interface. Spectral response and behavior at different light intensities of modified-P3HT cells suggest the polymer to be potentially more resilient than spiro-OMeTAD under fast neutron irradiation, once the perovskite/polymer is improved, although further investigations are needed to gain more insights and push the development and adoption of flexible PSCs for space and avionic applications.

Nanoscale Phase Separation in Ternary Organic Solar Cells Based on PTB7:PC70BM:IC70BA.

As a fullerene derivative, IC70BA is widely used in the ternary organic solar cells (TOSCs) to increase the open circuit voltage (Voc) of the devices. Unfortunately, most of the literature shows that IC70BA will lead to a reduction in the short-circuit current density (Jsc) and fill factor (FF). In this work, IC70BA is added to the PTB7:PC70BM binary system to form the ternary system, which is composed of one donor and two fullerene acceptors. Surprisingly, the addition of IC70BA does not immediately lead to a decrease in Jsc and FF. In fact, the appropriate weight ratio of IC70BA in fullerenes can simultaneously increase the Voc, Jsc, and FF of the TOSCs. The synergistic optimization of the surface and bulk morphology of the ternary active layer suppresses the attenuation of Jsc and FF. The smooth surface and suitable phase separation size effectively guarantee the separation, transport and extraction of the charge. Moreover, the addition of IC70BA can significantly improve the hole transport capacity of the active layer, and the optimal hole mobility is 5.13 - 10"4 cm²V-1S-1. Finally, the TOSCs with 10% weight ratio of IC70BA gives the optimal PCE of 9.24% and ideality factor of 2.3.

Effect of a silicon nitride film on the potential-induced degradation of n-type front-emitter crystalline silicon photovoltaic modules

We investigate the effect of silicon nitride (SiNx) films in n-type front-emitter (n-FE) crystalline Si (c-Si) solar cells on the potential-induced degradation (PID) of n-FE photovoltaic (PV) modules. A negative-bias PID test for a few min does not degrade the performance of PV modules with n-FE cells without SiNx/Si dioxide (SiO2) stacks, unlike in the case of PV modules with cells with SiNx/SiO2. This is because of the absence of polarization-type PID. After a longer PID test, the PV modules with n-FE cells without SiNx/SiO2 show a slower decrease in fill factor (FF), originating from Na introduction into the depletion layer of a p–n junction, than the modules with cells with SiNx/SiO2. The mitigation of PID by eliminating SiNx is partly consistent with the results of PV modules with p-type conventional cells without SiNx in which no PID occurs. SiNx thus has a function of enhancing Na introduction into c-Si.

Achieving Efficient Thick Film All-polymer Solar Cells Using a Green Solvent Additive

Advances in organic photovoltaic technologies have been geared toward industrial high-throughput printing manufacturing, which requires insensitivity of photovoltaic performance regarding to the light-harvesting layer thickness. However, the thickness of light-harvesting layer for all polymer solar cells (all-PSCs) is often limited to about 100 nm due to the dramatically decreased fill factor upon increasing film thickness, which hampers the light harvesting capability to increase the power conversion efficiency, and is unfavorable for fabricating large-area devices. Here we demonstrate that by tuning the bulk heterojunction morphology using a non-halogenated solvent, cyclopentyl methyl ether, in the presence of a green solvent additive of dibenzyl ether, the power conversion efficiency of all-PSCs with photoactive layer thicknesses of over 500 nm reached an impressively high value of 9%. The generic applicability of this green solvent additive to boost the power conversion efficiency of thick-film devices is also validated in various bulk heterojunction active layer systems, thus representing a promising approach for the fabrication of all-PSCs toward industrial production, as well as further commercialization.

Potential of very thin and high‐efficiency silicon heterojunction solar cells

AbstractThin crystalline silicon (c‐Si) solar cells are highly attractive for realizing light‐weight and flexible wafer‐based solar cells as well as for reducing the material cost. Silicon heterojunction (SHJ) architecture using hydrogenated amorphous silicon (a‐Si:H) is suitable for realizing very thin c‐Si cells, because of its capability of excellent surface passivation. In this work, the potential of very thin c‐Si solar cells is examined by characterizing SHJ solar cells with a wide range of thicknesses from 50 to 400 μm. A trade‐off between the open‐circuit voltage (VOC) and the short circuit current density (JSC) against wafer thickness is clearly observed in these SHJ cells, whereas a decrease in fill factor (FF) is found for thin SHJ cells below 80 μm. The loss analysis for the thin SHJ cells with numerical simulation clarifies that the infrared parasitic absorption loss due to the supporting layers is enhanced for thinner wafers, which limits the JSC in the thin SHJ cells. In addition, it is confirmed that the FF is more sensitive to surface recombination than the VOC, and this tendency becomes more pronounced with the decrease in the wafer thickness. A high efficiency of 22% is achieved in a SHJ solar cell with a thickness of only 46 μm, demonstrating a high potential for flexible high‐efficiency c‐Si solar cells.

Imaging performance of fractal structuresparse aperture arrays

The angular resolution of optical system is limited by the ratio of the wavelength to the aperture of the entrance pupil, indicating that the optical system with large aperture has a high spatial resolution. Sparse aperture imaging is one of the effective solutions to the problem that the telescope is bulky, heavy and difficult to manufacture. According to the self-similarity and multi-scale characteristics of fractal configuration, we propose a sparse aperture array and analyze its performance for synthetic aperture imaging system. In the array Golay-3 is used as a structural unit to expand a multi-layered fractal configuration in a self-similar manner. Given the analytical expression of the pupil function which is reduced by dimensionless parameters, we calculate the modulation transfer functions (MTFs), the practical cut-off frequencies and the middle spatial frequency characteristics of the fractal configuration under different fill factors and different outer layer rotational angles. We analyze both the MTF values and the performance parameters of the fractal structure for the cases of <i>N</i> = 3, 9, and 18, respectively. The results show that the decrease of fill factor does not significantly change the MTF curve nor the practical cutoff frequency in a range of fill factor between 0.0952 and 0.2246. The outer layer rotational angle has a periodicity, and the change in the angle has no large influence on the practical cutoff frequency. When the reduced aperture parameter is <inline-formula><tex-math id="M3">\begin{document}$ {d_0} = 1$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20190818_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20190818_M3.png"/></alternatives></inline-formula> and the fill factor is 22.46%, the middle spatial frequency of <i>N</i> = 18 array is more stable and the practical cut-off frequency is higher. Using the fractal self-similarity, the aperture of the system can be expanded effectively while maintaining the middle spatial frequency characteristics. The computing results are of scale invariance due to the adoption of the reduced aperture parameter.

Experimental investigation of charge transfer, charge extraction, and charge carrier concentration in P3HT:PBD-DT-DPP:PC70BM ternary blend photovoltaics

A sensitizer consisting of D-A structured polymer (PBD-DT-DPP) is assessed with P3HT:PC70BM solar cell. This polymer possesses a narrow energy band gap, which complements in absorption of P3HT:PC70BM binary blend. Use of PBD-DT-DPP as a sensitizer in the ternary blend OPV is reported earlier, which showed enhanced power conversion efficiency (PCE) in the conventional device structure. In this work, charge transfer and charge transport properties of the ternary blend (inverted device) for its improved performance are discussed in detail. Ternary blend system demonstrated an improved device performance (∼3.35%) as compared with the binary of P3HT:PC70BM devices (∼2.58%). Ternary blend devices showed enhanced short circuit current density (JSC) of ∼4 mA/cm2 relative to P3HT:PC70BM. To understand the reason for the decrease in fill factor (FF), mobility analysis using charge extraction with increasing linear voltage (CELIV) measurements were carried out. However, there is not much change in the open circuit voltage (VOC). Results indicate increased bimolecular recombination for the ternary blend, suggesting increased disorder in the morphology of ternary blend films. Time-resolved microwave conductivity (TRMC) measurement was utilized to understand the photoconductance properties of the ternary blend films. Interestingly, TRMC results showed binary PBD-DT-DPP:P3HT and PBD-DT-DPP:PC70BM mixtures possess similar transient photo-conductance to that of P3HT:PC70BM. Further, photoluminescence (PL) measurements were carried out to probe the charge transfer process in the blend systems. Capacitance-voltage results showed enhanced carrier concentration in ternary system. The detailed analysis showed that ternary system helps in improving the charge generation and charge transport and hence improved device performance.

Overcoming Fill Factor Reduction in Ternary Polymer Solar Cells by Matching the Highest Occupied Molecular Orbital Energy Levels of Donor Polymers

AbstractDespite the potential of ternary polymer solar cells (PSCs) to improve photocurrents, ternary architecture is not widely utilized for PSCs because its application has been shown to reduce fill factor (FF). In this paper, a novel technique is reported for achieving highly efficient ternary PSCs without this characteristic sharp decrease in FF by matching the highest occupied molecular orbital (HOMO) energy levels of two donor polymers. Our ternary device—made from a blend of wide‐bandgap poly[4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐2,5‐dioctyl‐4,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione) (PBDT‐DPPD) polymer, narrow‐bandgap poly[4,8‐bis[5‐(2‐ethylhexyl)‐2‐thienyl]benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐ 6‐diyl)] (PTB7‐Th) polymer, and [6,6]‐phenyl C70‐butyric acid methyl ester (PC70BM)—exhibits a maximum power conversion efficiency of 10.42% with an open‐circuit voltage of 0.80 V, a short‐circuit current of 17.61 mA cm−2, and an FF of 0.74. In addition, this concept is extended to quaternary PSCs made by using three different donor polymers with similar HOMO levels. Interestingly, the quaternary PSCs also yield a good FF (≈0.70)—similar to those of corresponding binary PSCs. This study confirms that the HOMO levels of the polymers used on the photoactive layer of PSCs are a crucial determinant of a high FF.

Theoretical study of c-GaN/GaAs single heterojunction solar cells

In this work a theoretical study of electrical behavior for a c-GaN/GaAs heterostructure as a photovoltaic device through a two-dimensional (2D) finite element numerical simulation is presented for a first time. I-V curves and electrical parameters like short circuit current (Isc), open circuit voltage (Voc), fill factor (FF) and efficiency (I·) were obtained for n-i-p and n-p heterostructures with different thicknesses and doping of the layers by modeling heterostructures with characteristics parameters of this materials previously reported. As a result, an increment on Isc was observed by extending the thickness of i-GaAs layer from 12 mA/cm 2 for thinner heterostructures to a maximum of ~32 mA/cm 2 for heterostructures with i-GaAs layer >3000 nm and a decrease in Voc and FF in the range from ~1.06 V and 0.89 for n-p heterostructures to 0.75 V and 0.7 respectively for thicker i-GaAs layers allowing estimate maximum efficiencies between 23 and 25% for n-i-p and n-p configurations, respectively. This study allows demonstrating the potential of this type of heterostructures for solar cells applications, considering the possibility of using p-doping GaAs substrates for photovoltaics based in GaN. Keywords: GaN/GaAs, heterostructures, TCAD modeling, I-V curves, solar cell.

Control of Cu doping and CdTe/Te interface modification for CdTe solar cells

Copper doping in polycrystalline CdTe thin films and optimal band alignment at the CdTe/back-contact interface are critical for obtaining high performance devices. A CuCl2 solution treatment was used in this work to enhance the p-doping of CdTe. The carrier density of CdTe was increased from 4.72 × 1013 to 1.11 × 1014cm−3 and the open circuit voltage of the device was obviously improved more than ~50mV from 728 to 783mV. In order to further improve device performance, Te/Cu bilayer using rapid thermal processing was implemented to reduce barrier at the back contact. The short time-high temperature process efficiently activated the Te/Cu bilayer back contact and precisely controlled the Cu diffusion. The proper dose of Cu diffusion can further increase the p-doping of CdTe (~2.22 × 1014cm−3), resulting in the apparent increase in response from the CdS spectral region. The chemical reaction occurred between Te and Cu after rapid thermal processing treatments causing the formation of the CuxTe phases, which can form a barrier in the conduction band to reflect electrons and reduce recombination at the back contact. With the increase of the temperature, the open circuit voltage of the device increased. However, the device with excessive Cu contacted at higher temperature showed the reduction in response in the long-wavelength region and decrease in fill factor due to the formation of much more Cu-related recombination states. Finally, open circuit voltage of > 820mV, and fill factor of > 72% for CdTe solar cells with an area of 0.24cm2 were achieved.

Cu(In,Ga)Se2 Solar Cells with Amorphous In2O3-Based Front Contact Layers.

Amorphous (a-) In2O3-based front contact layers composed of transparent conducting oxide (TCO) and transparent oxide semiconductor (TOS) layers were proved to be effective in enhancing the short-circuit current density (Jsc) of Cu(In,Ga)Se2 (CIGS) solar cells with a glass/Mo/CIGS/CdS/TOS/TCO structure, while maintaining high fill factor (FF) and open-circuit voltage (Voc). An n-type a-In-Ga-Zn-O layer was introduced between the CdS and TCO layers. Unlike unintentionally doped ZnO broadly used as TOS layers in CIGS solar cells, the grain-boundary(GB)-free amorphous structure of the a-In-Ga-Zn-O layers allowed high electron mobility with superior control over the carrier density (N). High FF and Voc values were achieved in solar cells containing a-In-Ga-Zn-O layers with N values broadly ranging from 2 × 1015 to 3 × 1018 cm-3. The decrease in FF and Voc produced by the electronic inhomogeneity of solar cells was mitigated by controlling the series resistance within the TOS layer of CIGS solar cells. In addition, a-In2O3:H and a-In-Zn-O layers exhibited higher electron mobilities than the ZnO:Al layers conventionally used as TCO layers in CIGS solar cells. The In2O3-based layers exhibited lower free carrier absorption while maintaining similar sheet resistance than ZnO:Al. The TCO and TOS materials and their combinations did not significantly change the Voc of the CIGS solar cells and the mini-modules.

Enhanced performance of SubPc planar heterojunction solar cells with a novel luminescent sensitizer of 4,4′-bis[(N-carbaz ole)styryl]biphenyl

Here, the conventional luminescent material 4,4′-bis[(N-carbazole) styryl] biphenyl (BSB-Cz) is used as luminescent sensitizer in boron subphthalocyanine chloride (SubPc)/C60 planar heterojunction (PHJ) solar cells for the first time. When inserting 3-nm BSB-Cz between the MoO3 and donor layer, the power conversion efficiency (PCE) of SubPc/C60 PHJ is improved from 1.21% to 1.72%. BSB-Cz at 3–8nm all enhances the short-circuit current (JSC) and open-circuit voltage. As BSB-Cz is capable of absorbing short-wavelength solar light and re-emitting long-wavelength light which is exactly located at the absorption wavelength range of SubPc and C60. The JSC increase is attributed to the electron-blocking effect of BSB-Cz together with matched photoluminescence spectrum of BSB-Cz and the absorption spectra of SubPc as well as C60, which enhances the incident photon number for SubPc and C60. AFM images indicate that the bumpy surface of 3-nm BSB-Cz is filled in by the subsequent SubPc layer, thus decreases the surface roughness. However, thicker BSB-Cz results in significantly increased RMS roughness with decreased fill factor. The thickness of BSB-Cz maybe decides the only donor or two competing donors at the donor/acceptor interface, which affects the exciton disociattion and recombination in the overall device.

Structural color-tunable mesoporous bragg stack layers based on graft copolymer self-assembly for high-efficiency solid-state dye-sensitized solar cells

We present a facile fabrication route for structural color-tunable mesoporous Bragg stack (BS) layers based on the self-assembly of a cost-effective graft copolymer. The mesoporous BS layers are prepared through the alternating deposition of organized mesoporous-TiO2 (OM-TiO2) and -SiO2 (OM-SiO2) films on the non-conducting side of the counter electrode in dye-sensitized solar cells (DSSCs). The OM layers with controlled porosity, pore size, and refractive index are templated with amphiphilic graft copolymers consisting of poly(vinyl chloride) backbones and poly(oxyethylene methacrylate) side chains, i.e., PVC-g-POEM. The morphology and properties of the structural color-tunable mesoporous BS-functionalized electrodes are characterized using energy filtered transmission electron microscopy (EF-TEM), field emission-scanning electron microscopy (FE-SEM), spectroscopic ellipsometry, and reflectance spectroscopy. The solid-state DSSCs (ssDSSCs) based on a structural color-tunable mesoporous BS counter electrode with a single-component solid electrolyte show an energy conversion efficiency (η) of 7.1%, which is much greater than that of conventional nanocrystalline TiO2-based cells and one of the highest values for N719 dye-based ssDSSCs. The enhancement of η is due to the enhancement of current density (Jsc), attributed to the improved light harvesting properties without considerable decrease in fill factor (FF) or open-circuit voltage (Voc), as confirmed by incident photon-to-electron conversion efficiency (IPCE) and electrochemical impedance spectroscopy (EIS).