Fill Factor Of Solar Cells Research Articles

Accuracy of Contact Resistivity Measurements for Electron-Selective Titanium Oxide Contacts in n-Type c-Si Solar Cell

Contact resistivity quantifies the charge transport barrier, which is one of the key parameters for choosing the carrier selective contact for silicon solar cells. Optically transparent and electrically selective contacts such as transition metal oxide (TMO)-based contacts are employed in solar cell applications. Therefore, the extraction of contact resistivity for such Schottky contacts requires apposite validation. In this article, we have extracted the contact resistivity of TiOx/LiFx/Al stack over n-type c-Si wafer using two conventional techniques: 1) Shockley's transfer length method (TLM) and 2) Cox and Strack method (CSM). The extracted contact resistivity is validated by comparing with the solar cell's contact resistivity ( true contact resistivity) and fill factor (FF). We found that TLM overestimates the contact resistivity for highly resistive TiOx films, due to the asymmetrical nature of the TMO barrier and correlated with the reported experimental data. In contrast, CSM extracts more accurate contact resistivity for TiOx contacts when total resistance is extracted closer to the J mpp (38 mA cm−2). Besides, we recommend including the passivating layer along with the contacts (in the case of passivating contacts) to extract the actual contact resistivity felt by the solar cell.

Nanoscale localized contacts for high fill factors in polymer-passivated perovskite solar cells.

Polymer passivation layers can improve the open-circuit voltage of perovskite solar cells when inserted at the perovskite-charge transport layer interfaces. Unfortunately, many such layers are poor conductors, leading to a trade-off between passivation quality (voltage) and series resistance (fill factor, FF). Here, we introduce a nanopatterned electron transport layer that overcomes this trade-off by modifying the spatial distribution of the passivation layer to form nanoscale localized charge transport pathways through an otherwise passivated interface, thereby providing both effective passivation and excellent charge extraction. By combining the nanopatterned electron transport layer with a dopant-free hole transport layer, we achieved a certified power conversion efficiency of 21.6% for a 1-square-centimeter cell with FF of 0.839, and demonstrate an encapsulated cell that retains ~91.7% of its initial efficiency after 1000 hours of damp heat exposure.

Binary non-fullerene-based polymer solar cells with a 430 nm thick active layer showing 15.39% efficiency and 73.38% fill factor

High hole mobility polymer and Y-series non-fullerene acceptor boost efficiency and fill factor of thick-film polymer solar cells.

Increasing Molecular Packing Density and Dielectric Constant in Non-Fullerene Acceptors Enables to Boost the Fill Factor Approaching 0.82 in Organic Solar Cells

SUMMARYThe fill factor (FF) of organic solar cells (OSC), a critically important photovoltaic parameter, is yet sub-optimal, often less than 0.8. To further reduce the FF gaps with regard to the Shockley-Queisser upper limit, we present a study unveiling the impacts of dielectric properties on obtaining high FFs and photovoltaic efficiencies in OSCs. With increasing the dielectric constant (e) of non-fullerene acceptors (NFAs) and bulk heterojunction (BHJ) films, afforded by the increase of molecular packing density (MPD) of NFAs in solid states, we show that the FF penalties related to non-geminate charge recombination in OSCs can be appreciably mitigated. This conceptual modulation on FFs is embodied by a series of NFA-based BHJs where the differentiated MPDs and resultant changes of e in BHJs are reflected by the difference in FFs. In particular, as exemplified by an NFA model system L8-BO tailored with branched side chains, the enlargements of MPD and e allow to achieve an impressive FF of 0.815 with efficiency of 18.23% in OSCs featuring an impressively low bimolecular recombination and reduced sensitivity of FF on the BHJ film thickness.

Crystallization driven boost in fill factor and stability in additive-free organic solar cells.

The control of morphology and microstructure during and after the active layer processing of bulk-heterojunction solar cells is critical to obtain elevated fill factors and overall good device performance. With the recent development of non-fullerene acceptors, wide attention has been paid to improve miscibility, solubility and nanoscale separation by laborious molecular design processes and by the use of additives. Nonetheless, several post-processing strategies can equally contribute to obtain an optimum phase separation and even to an enhanced crystallinity, but their effect on performance and device lifetime of polymer/non-fullerene acceptor solar cells is still unclear. Herein, we report a systematic comparison between different post-processing treatments including thermal annealing (TA), vacuum drying (VD) and solvent vapor annealing (SVA) on the TPD-3F polymer and IT-4F non-fullerene acceptor, comparing their effects on device performance as well as on the morphology and optical and electrical properties. The optimized SVA treated devices exhibited power conversion efficiencies close to 14% with a remarkable 76% fill factor and superior short-circuit currents compared to the one of untreated devices. Moreover, SVA demonstrated improvements in device stability both under illumination and under ambient conditions. The induced phase separation and the increased crystallinity of the acceptor molecules, as revealed by GIWAXS measurements, led to increased photogenerated currents, with a more effective exciton dissociation and charge collection. The open-circuit voltage losses in the SVA and TA devices were explained by a bandgap reduction and a higher trap-assisted recombination, respectively. Overall, our study points to the role of post-processing in organic solar cell fabrication, and contributes towards a new generation of efficient and stable additive-free organic solar cells.

Fabrication of bulk heterojunction organic photovoltaic and effect of buffer layer on the basic solar cell parameters

The poly(3-hexylthiophene-2,5-diyl):phenyl C61 butyric acid methyl ester (P3HT:PCBM) organic material is important for BHJ organic solar cells. In this study PEDOT:PSS layer was coated on ITO using spin coater and thereon coated P3HT:PCBM (1:1) as fotoactive layer. Finally, Al contacts have been evaporated for electrical measurements and device structure completed. In other example, 2 nm LiF evaporated on P3HT:PCBM before metal. Electrical characterization of the devices performed with current density–voltage (J–V) measurement at room temperature and a solar simulator under an 100 mW/cm2 irradiation intensity. Basic solar cells parameters as short circuit current density (JSC), open circuit voltage (VOC), fill factor (FF) and power conversion efficiency (PCE) of the organic solar cells were determined with the measurement. Efficiency of organic solar cells increased 0.85% to 1.87% using LiF as buffer layer. Similary, LiF layer was increased other parameters of device and obtained more stabil the device.

Effects of intensity of magnetic field generated by neodymium permanent magnet sheets on electrical characteristics of monocrystalline silicon solar cell

<span>In this research, the effects of magnetic field intensity on electrical characteristics of a monocrystalline silicon solar cell were investigated. The experimental test-rig under Standard Test Condition was set up and tested to observe the respective effects. The electrical characteristics in terms of current-voltage-power curves, critical solar cell parameters and fill factor were then examined and analyzed. The outcome of this study demonstrates that the external magnetic field has a positive impact on electrical parameters, the experimental results showed that applying magnetic intensity of 60-260mT significantly affected the electrical characteristics of the cell; i.e., maximized cell current, voltage and power by 12.20, 7.12 and 23.60%, respectively. In addition, this positive impact consequencely happened on the i-v and p-v electrical characteristics curves of the solar cell; reflected by 3.69% increasing in the fill factor. </span>

Effect of energetic distribution of trap states on fill factor in perovskite solar cells

Fill factor is a critical parameter for characterizing the performance of perovskite solar cells and is speculated to be closely related to the trap states, while the underlying correlation remains unclear. In this work, the effect of the energetic distribution of trap states in perovskite on the fill factor of the device is systemically investigated. Perovskite films with distinct trap states are prepared with/without the dimethyl sulfoxide additive, based on which the corresponding devices exhibit different power conversion efficiency and fill factors, but similar open-circuit voltages and short-circuit currents. Subsequently, the recombination dynamics process, trapping/detrapping efficiency and transport property of the photo-generated charge carrier are fully studied. Moreover, it is found that the difference in the energetic distribution of trap states leads to the variation of charge recombination/transport dynamics. The energetic distribution of trap states also determines the activation energy of thermal-assisted carrier detrapping and charge collection efficiency, which further affects the FF behavior. The passivation of trap state, especially deep trap states, could reduce the charge recombination loss, make the charge detrapping process more efficient, modify the charge transport property, improve the charge collection efficiency and eventually lead to the enhancement of FF.

Novel small oligothiophene molecules with phenylene and naphthalene cores as promising absorber materials for organic solar cells

New small molecules bearing either phenylene or naphthalene core in combination with thiophene and rhodanine periphery moieties were synthesized by the Stille cross-coupling reaction. Their evaluation for prototypes of organic solar cells showed that replacing phenylene moiety by the naphthalene one caused decrease in the HOMO energy, while the open-circuit voltage and fill factors of solar cells based on these materials were significantly improved to manifest maximum power conversion efficiencies to 5.3%.

Relationship between Fill Factor and Light Intensity in Solar Cells Based on Organic Disordered Semiconductors: The Role of Tail States

The origin of the relationship between fill factor (FF) and light intensity (I) in organic disordered-semiconductor-based solar cells is studied. An analytical model describing the balance between transport and recombination of charge carriers, parameterized with a factor, ${\mathrm{\ensuremath{\Gamma}}}_{m}$, is introduced to understand the FF-I relation, where higher values of ${\mathrm{\ensuremath{\Gamma}}}_{m}$ correlate to larger FFs. Comparing the effects of direct and tail-state-mediated recombination on the FF-I plot, we find that, for low-mobility systems, direct recombination with constant transport mobility can deliver only a negative dependence of ${\mathrm{\ensuremath{\Gamma}}}_{m,\mathrm{dir}}$ on light intensity. By contrast, tail-state-mediated recombination with trapping and detrapping processes can produce a positive ${\mathrm{\ensuremath{\Gamma}}}_{m,t}$ versus sun dependency. The analytical model is validated by numerical drift-diffusion simulations. To further validate our model, two material systems that show opposite FF-I behavior are studied: poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b;4,5-b\ensuremath{'}]dithiophene-2,6-diyl-alt-[4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2-carboxylate-2-6-diyl]} (PTB7-Th):[6,6]-phenyl-${\mathrm{C}}_{71}$-butyric acid methyl ester (${\mathrm{PC}}_{71}$BM) devices show a negative FF-I relation, while PTB7-Th:(5Z,5\ensuremath{'}Z)-5,5\ensuremath{'}-{[7,7\ensuremath{'} -(4,4,9,9-tetraoctyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b\ensuremath{'}]dithiophene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole-7,4-diyl)]bis(methanylylidene)}bis(3-ethyl-2-thioxothiazolidin-4-one) (O-IDTBR) devices show a positive correlation. Optoelectronic measurements show that the O-IDTBR device presents a higher ideality factor, stronger trapping and detrapping behavior, and a higher density of trap states, relative to the ${\mathrm{PC}}_{71}$BM device, supporting the theoretical model. This work provides a comprehensive understanding of the correlation between FF and light intensity for disordered-semiconductor-based solar cells.

Synergistic Effect through the Introduction of Inorganic Zinc Halides at the Interface of TiO2 and Sb2S3 for High-Performance Sb2S3 Planar Thin-Film Solar Cells.

The competition between charge recombination and extraction principally affects the fill factor (FF) and power conversion efficiency (PCE) of planar thin-film solar cells. In Sb2S3 thin-film solar cells, the electrocharge recombination and extraction n transport layer (ETL) plays a significant role in electron extraction and determination of Sb2S3 film absorber quality. Herein, a TiO2 ETL is strategically modified using an inorganic salt zinc halide (i.e., ZnCl2, ZnBr2, ZnI2), which simultaneously improves the electronic properties of TiO2 and promotes the growth of Sb2S3 films with larger grain size and higher crystallinity. The experimental results and theoretical calculations further reveal that the zinc halide can interact with TiO2 and simultaneously bond strongly with the upper Sb2S3 film, which creates a unique pathway for electron transfer, passivates the trap states, and alleviates the recombination losses effectively. As a result, an average PCE of 6.87 ± 0.11% and the highest PCE of 7.08% have been attained with an improved FF from 51.22 to 61.61% after ZnCl2 introduction. Additionally, introduction of ZnCl2 helps the unencapsulated devices to maintain 93% of their original performance after 2400 h of storage in a nitrogen-filled glovebox. This work develops an effective route for the optimization of ETLs and defect healing using simple and low-cost inorganic salts.

Effects of Bulk Heterojunction Morphology Control via Thermal Annealing on the Fill Factor of Anthracene-based Polymer Solar Cells

Here we report a polymeric semiconductor (ODATT) comprising alkoxy anthracene (ODA) and thienothiophene (TT) polymerized by stille coupling reaction with the Pd catalyst. The optical properties of the polymer: PC71BM blend films are used by the UV-Visible absorption spectroscopy. The ODATT blends with PC71BM exhibit a maximal power conversion efficiency of 2.2% via thermal annealing treatment. Morphological analysis of the polymer: PC71BM blend films demonstrate the influence of ODATT polymer segregation on device performance by atomic force microscopy and transmission electron microscopy. We confirmed that ODATT has enhanced fill factor after thermal annealing treatment from the reduced series and shunt resistance from morphological enhancement.

A Numerical Fitting-Based Compact Model: An Effective Way to Extract Solar Cell Parameters

We have developed an electrical circuit-based compact numerical fitting model to determine industry-related physical parameters of solar cells utilizing only 3–8 current–voltage coordinate points without any specific selection of an experimental coordinate axis. The proposed compact numerical fitting model was effectively tested to determine the peak power point, fill factor and efficiencies for organic and inorganic solar cells, as well as for solar panels. This research facilitates cost-effective energy management of solar modules and farms.

Large Conduction Band Energy Offset Is Critical for High Fill Factors in Inorganic Perovskite Solar Cells

Although SnO2 has been reported to give high efficiencies of over 20% for organic–inorganic perovskite solar cells and has been frequently used in perovskite tandem solar cells, very few contributi...

Dominant recombination mechanism in perovskite solar cells: A theoretical study

Different recombination losses have been shown to play a role in the photocurrent and photovoltage loss of lead halide perovskite solar cells. While it is believed that trap density is extremely small in high-efficiency perovskite cells, trap-assisted recombination cannot be ruled out due to the existence of tail states, for instance at the grain boundaries. In this study, the optical and electrical performance of a perovskite solar cell of the structure: ITO/PEDOT:PSS/CH3NH3PbI3/PC61BM/LiF/Al was modelled using numerical drift-diffusion simulations with embedded optical modelling via the transfer matrix method. The total recombination was calculated as the sum of bimolecular recombination and recombination via tail states. The influence of charge carrier mobility on photovoltaic parameters (short-circuit current, fill factor, open-circuit voltage, and power conversion efficiency) of perovskite solar cells was studied. Next, the impact of Urbach energy on the recombination process was investigated by simulation of bimolecular and tail state recombination rates as a function of voltage for various values of Urbach energy. It was shown that by increasing the Urbach energy, the bimolecular recombination rate decreases, but the tail state recombination rate increases at all voltages. Furthermore, the slope of the open-circuit voltage-light intensity curve, the light ideality factor, demonstrates the dominant recombination at different Urbach energy levels. It was found that the slope increases from 1.04 at EU = 25 meV to1.65 at EU = 150 meV. It can be concluded that the bimolecular recombination is the dominant recombination at low EU, while the tail state recombination overcomes the bimolecular recombination at high EU.

Edge effect in silicon solar cells with dopant-free interdigitated back-contacts

Dopant-free heterojunction opens new doors to highly efficient silicon solar cells with interdigitated back-contacts (IBC) via an easy hard-mask processing. However, the existence of inevitable overlap between the hole- and electron-transport layers may cause edge leakage and recombination, which will deteriorate the power conversion efficiency. Here we unambiguously determined the edge recombination and recombination losses quantitatively, in combination with detailed comparisons in photovoltaic parameters, dark and light current-voltage ( I–V ) curves, partially illuminated I–V curves, of the hard-mask processed and the lithography processed IBC devices. Without the interfacial passivation layer, the solar cells fabricated by the hard-mask method suffer severe edge recombination with loss of 3 × 10 −4 A and a quite poor fill factor ( FF ) of ~66%, suggesting that the edge recombination could be another important issue affecting the FF besides the series resistance. With the clear understanding of the edge effect, we finely control the edge overlap, and finally obtained silicon dopant-free solar cells (with of intrinsic amorphous silicon as passivation layer) with over 20% efficiency and 73% FF either by lithography or by hard-mask methods. • Figuring out the edge recombination is one of the important items affecting the Fill Factor in IBC-DFHJ solar cells. • A series of new methods are provided to quantitatively and positionally analyze this edge recombination. • By well suppressing the edge recombination, IBC-DFHJ solar cells with a promising PCE of 20.6% was realized.

Improving the performance of Cu2ZnSnS4 thin film solar cell by engineering the ITO film thickness

In this work, the effects of tin doped indium oxide (ITO) thin films with different thicknesses (50 nm–476 nm) on the optoelectronic performance were investigated. Meanwhile, the sputtered ITO layers were annealed at 180 °C for 60min under air atmosphere. The result indicated that the electro-optical properties of ITO films with the thickness (383 nm) were optimum, and the corresponding resistivity and average reflectance in the spectrum range (350–860 nm) were 4.73 × 10−4 Ω cm and lower than 20%, respectively. Finally, impacts of ITO layers with various thicknesses on the performance of CZTS solar cells were also studied. The open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and power conversion efficiency (PCE) of CZTS solar cells had been increased significantly from 576 mV to 636 mV, from 15.8 mA/cm2 to 20.2 mA/cm2, from 31.2% to 43.4% and from 3.04% to 5.56%, respectively, and eventually the highest PCE of CZTS solar cell based on 383 nm ITO window layer thickness was 5.56%.

Study on the improvement of p-type multi-crystalline silicon material for solar cells by the hydrogenation with electron injection

In this paper, we have found that the efficiency of p-type mono-crystalline silicon (mono-Si) passivated emitter and rear contact (PERC) solar cells can be increased by $$0.12{\%}_{\mathrm {{abs.}}}$$ with the process of hydrogenation with electron injection (HEI). However, the same scheme was not suitable for p-type multi-crystalline silicon (mc-Si) solar cells. To promote power conversion efficiency (PCE) for the mc-Si solar cells, we have explored a developed HEI process for the mc-Si solar cells to improve the device performance. Meanwhile, we also analysed the mechanization inside the solar cells after applying the HEI process. Through the design of experiment (DOE), the correlation among injection current, temperature, injection time and efficiency improvement was analysed in detail. It was proved that mc-Si solar cells require higher current injection and temperature to passivate the complex impurities in the bulk, when compared to mono-Si solar cells. With the optimal scheme explored by this paper, the open circuit voltage ( $$U_{\mathrm {{oc}}}$$ ), short circuit current density ( $$J_{\mathrm {{sc}}}$$ ) and fill factor (FF) of p-type mc-Si solar cells, respectively, increased by 1.2 mV, 0.11 mA $$\hbox {cm}^{-\mathrm {{2}}}$$ and $$0.05{\%}_{\mathrm {{abs.}}}$$ , respectively. The efficiency was improved about $$0.11 \pm 0.005{\%}_{\mathrm {{abs.}}}$$ . These results will provide a certain method and basis for further improving the efficiency of mc-Si PERC cells and overcoming the light-elevated temperature-induced degradation by HEI process.

Influence of Interfacial Oxides at TCO/Doped Si Thin Film Contacts on the Charge Carrier Transport of Passivating Contacts

Minimizing transport losses in novel solar cell concepts is often linked to improvements at the transparent conductive oxide (TCO)/doped silicon contact. A detailed understanding of the determining factors for an efficient transport at this heterojunction is essential, such as work function matching and efficient tunneling transport. In this article, we analyze the different TCO contact parameters experimentally and by numerical device simulations. We show that work function matching by using a proper interlayer [e.g., tungsten oxide (WO x )] can be an effective means to improve the fill factor of silicon heterojunction solar cells. However, we showcase that an improved work function matching achieved by changing the doping of a TCO interlayer can be superimposed by a less efficient tunneling transport, for e.g., due to an interfacial oxide. Furthermore, we show that for n-tunnel oxide passivating contacts, an unintentionally grown oxide at the TCO/poly-Si contact could be a possible explanation for recently observed transport losses.

Simulation of Thin-Film Solar Cells with a CuInSe2 Chalcopyrite Structure

By using numerical simulation, the operating temperatures of a thin-film solar cell based on CuInSe2 have been determined and the solar radiation density values, at which stabilization of the temperature operating conditions of the thin-film solar cell is not required, have been optimized. The maximum possible efficiency value of ~14.8 % is achieved under actual operating conditions, and is maintained by the incoming thermal energy as both emitted in this cell and infrared radiation of the sun and the environment. A model of the proposed thin-film solar cell was implemented in the COMSOL Multiphysics program environment with the use of the Heat Transfer Module. The operating temperatures of the solar cell without thermal stabilization under conditions of the diurnal and seasonal variations of both the ambient temperature and the power density of the AM1.5 solar spectrum have been determined. The maximum value of this power density was varied from 1.0 to 500 kW/m2 when using concentrators. The obtained values of operating temperatures of the thin-film solar cell were used to determine its main parameters in the SCAPS-1D program. The graphs of the operating temperature, efficiency and fill factor of the thin-film solar cell versus the solar radiation density are provided. It is shown that in order to obtain the highest possible efficiency of a solar cell, it is necessary to use concentrated solar radiation with a power density, the maximum value of which should be 8 kW/m2 in July and 10 kW/m2 in January. In the case of lower and higher values of power density, an appropriate thermal stabilization of the cell under consideration is necessary. The dependencies of efficiency, fill factor and open-circuit voltage versus the stabilization temperature of the solar cell, temperature gradients at the interfaces of the thermoelectric layer were also calculated. It is shown that by choosing optimal values of the thermal stabilization, the efficiency of the proposed solar cell may be about 15 % or more.