Performance Of Heterojunction Solar Cells Research Articles

Insights into the Heat‐Assisted Intensive Light‐Soaking Effect on Silicon Heterojunction Solar Cells

Heat‐assisted intensive light soaking has been proposed as an effective posttreatment to further enhance the performance of silicon heterojunction (SHJ) solar cells. In the current study, it is aimed to distinguish the effects of heat and illumination on different (doped and undoped) layers of the SHJ contact stack. It is discovered that both elevated temperature and illumination are necessary to significantly reduce interface recombination when working effectively together. The synergistic effect on passivation displays a thermal activation energy of approximately 0.5 eV. This is likely due to the photogenerated electron/hole pairs in the c–Si wafer, where nearly all of the incident light is absorbed. By distinguishing between the effects of light and heat effects on the conductivity of p‐ and n‐type doped hydrogenated amorphous silicon (a–Si:H) layers, it is demonstrated that only heat is accountable for the observed rise in conductivity. According to numerical device simulations, the significant contribution to the open‐circuit voltage enhancement arises from the reduced density of defect states at the c–Si/intrinsic a–Si:H interface. In addition, the evolution of the fill factor is highly dependent on changes in interface defect density and the band tail state density of p‐type a–Si:H.

Impact of Texture Height and Ozone-Based Rounding on Silicon Heterojunction Solar Cells Performance

In this study, the effect of ozone-based rounding was investigated for three random-pyramid texture height ranges for Silicon Heterojunction (SHJ) at the cell and module levels. In a first experiment, 5 ozone-based rounding process times (0, 2, 4, 6, 8 and 10 minutes) were applied to two texture-height ranges (Small and Medium) to observe variations in the reflection response of the wafers. In a second experiment, 3 ozone-based rounding treatment times (0, 2 and 6 minutes) were applied to three texture-height ranges (Small, Medium and Large) and to observe the results both on the cell and on the module levels. The first experiment has shown that ozone-based rounding increases reflection and has a more pronounced effect for smaller than larger sized texture-heights. An increase in the minimum wavelength of reflection is seen after the Transparent Conductive Oxide (TCO) deposition, indicating that shorter deposition times can be used. The results of the second experiment show that, even though the Short-Circuit Current (Jsc) decreases for the three textures with rounding time, it is compensated by an increase in the pseudo-Fill-Factor (pFF). A maximum is seen at the cell level for 2 minutes of rounding for the small and large texture sizes, but which is leveled at the module. In conclusion, these results indicate that 2 minutes of ozone-based rounding can be beneficial for the cell’s final efficiency as the improvement in passivation still compensates the optical losses resulting in a lower Jsc.

Role of Al doping in morphology and interface of Al-doped ZnO/CuO film for device performance of thin film-based heterojunction solar cells

Al-doped ZnO (AZO) at different doping concentrations are synthesized by the chemical bath deposition process. The X-ray diffraction results are confirmed the formation of hexagonal structure of ZnO. The doping concentration of Al in ZnO is varied the shape and size of AZO structures. These AZO structures are used for the fabrication of the heterojunction (ZnO/CuO) solar cell. The photoluminescence results are shown a smaller number of defects in AZO thin films. The potential barrier and ideality factor are obtained at 0.855 eV and 2.89 for 3 mol% doping of Al-doped thin-film solar cell diode. The interface of ZnO/CuO is analyzed by impedance spectra and Capacitance-frequency results. The maximum efficiency for device is recorded with a high fill factor at 3 mol% Al doped ZnO thin film based solar cell. This increased in the power conversion efficiency of device is originated from enhanced the optical properties, outstanding charge extraction efficiency, and suppressed the recombination of charge on the interface of CuO and AZO (3 mol%) layers, as revealed by the measurement of electrical, optical, and impedance spectroscopy.

Improved interface microstructure between crystalline silicon and nanocrystalline silicon oxide window layer of silicon heterojunction solar cells

N-type hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) is potential to enhance the performance of silicon heterojunction solar cells, but the raised plasma damage on underlying layer during the nc-SiOx:H deposition with a high-volume fraction of hydrogen is a burning issue. The underlying intrinsic hydrogenated amorphous silicon (i-a-Si:H) bilayer between n-type crystalline silicon (c-Si) and n-type nc-SiOx:H has been investigated by modulating silane (SiH4) gas flow rate (GFR) of interface porous layer. It has been found that the initial H-rich i-a-Si:H bilayer deposited by interfacial 1600 sccm GFR with relatively stable larger voids diameter and less voids number density can not only withstand hydrogen ions bombardment but also passivate c-Si surface well. Meanwhile, it also has been verified that the optimal n-seed deposition can further enhance both total hydrogen content and hydrogen content in compact structure to promote c-Si surface passivation and carrier transportation. The optimized SiH4 GFR for the interfacial i-a-Si:H growth and the appropriate deposition time of n-seed layer have been applied into the front passivation layer of silicon heterojunction solar cells, thus a high efficiency of approximate 25 % with high VOC and FF has been achieved.

A CTL-free homo-heterojunction antimony chalcogenide solar cell: Theoretical study

Exploring antimony chalcogenide as photovoltaic (PV) absorber material for solar cell is an appealing strategy. However, the conversion efficiency (η) of antimony chalcogenide solar cells including antimony selenide (Sb2Se3), antimony sulfide (Sb2S3) and antimony sulfide–selenide (Sb2(S,Se)3) lag far behind their Shockley−Queisser limit efficiency. Generally, the device PV performance of thin film heterojunction solar cells is mainly affected by the material properties of each functional layer, as well as the device architecture and heterointerface characteristics. Herein, a novel homo-heterojunction antimony chalcogenide solar cell without any carrier transport layer (CTL) consisting of FTO/(n)Sb2Se3/(p)Sb2Se3/(p)Sb2S3/Metal has been proposed. The influence of thickness, doping concentration and bulk defect density of the functional layer materials, the interface defect density at (p)Sb2Se3/(p)Sb2S3 heterointerfaces, and back contact metal work function on device PV performance have been theoretically analyzed utilized wxAMPS software. After optimization, the proposed solar cell has an open-circuit voltage (Voc) of 0.885 V, a short-circuit current density (Jsc) of 36.14 mAcm−2, a filling factor (FF) of 84.30 %, and a η of 26.97 %. These results indicate that the novel homo-heterojunction antimony chalcogenide solar cell without any CTL have the potential to become a high-efficiency PV device.

Charge-Transfer State Dissociation Efficiency Can Limit Free Charge Generation in Low-Offset Organic Solar Cells.

We investigate the charge-generation processes limiting the performance of low-offset organic bulk-heterojunction solar cells by studying a series of newly synthesized PBDB-T-derivative donor polymers whose ionisation energy (IE) is tuned via functional group (difluorination or cyanation) and backbone (thiophene or selenophene bridge) modifications. When blended with the acceptor Y6, the series present heterojunction donor-acceptor IE offsets (ΔEIE) ranging from 0.22 to 0.59 eV. As expected, small ΔEIE decrease nonradiative voltage losses but severely suppresses photocurrent generation. We explore the origin of this reduced charge-generation efficiency at low ΔEIE through a combination of opto-electronic and spectroscopic measurements and molecular and device-level modeling. We find that, in addition to the expected decrease in local exciton dissociation efficiency, reducing ΔEIE also strongly reduces the charge transfer (CT) state dissociation efficiency, demonstrating that poor CT-state dissociation can limit the performance of low-offset heterojunction solar cells.

Impact of Graphene Monolayer on the Performance of Non-Conventional Silicon Heterojunction Solar Cells with MoOx Hole-Selective Contact.

In this work, a new design of transparent conductive electrode based on a graphene monolayer is evaluated. This hybrid electrode is incorporated into non-standard, high-efficiency crystalline silicon solar cells, where the conventional emitter is replaced by a MoOx selective contact. The device characterization reveals a clear electrical improvement when the graphene monolayer is placed as part of the electrode. The current-voltage characteristic of the solar cell with graphene shows an improved FF and Voc provided by the front electrode modification. Improved conductance values up to 5.5 mS are achieved for the graphene-based electrode, in comparison with 3 mS for bare ITO. In addition, the device efficiency improves by around 1.6% when graphene is incorporated on top. These results so far open the possibility of noticeably improving the contact technology of non-conventional photovoltaic technologies and further enhancing their performance.

Understanding Silicon Heterojunction Solar Cells with nc‐SiC/SiO2as an Alternate Transparent Passivating Front Contact and Computational Design Optimization

The potential performance of silicon heterojunction solar cells applying transparent passivating contact (TPC) at the front side, based on a nc‐SiC:H/SiO2layer stack, is modeled and investigated. Herein, a complete multiscale electro‐optical device model of TPC solar cells is developed. The model is then used to understand and analyze such cells and search for potential conversion efficiency improvement paths. The influences of contact layer thicknesses and other properties on device performance are studied. An algorithm‐based optimization of cell electro‐optical performance is performed. It is implemented by coupling a genetic algorithm with a finite element method‐based TPC solar cell device model. Optimum front contact layer thicknesses are calculated. For optically optimized TPC contact layer thicknesses, an optical improvement of around 0.5 mA cm−2is found. Moreover, for complete electro‐optical optimization of TPC layers, about 0.27% absolute value increment in power conversion efficiency is calculated. At the rear side, proper designing of optimizing carrier transport using active dopant concentration of p‐type a‐Si:H layer and indium tin oxide layer has shown a potential to reach power conversion efficiency beyond 25%.

The use of back surface field and passivation layer to enhance the performance of silicon heterojunction solar cells

c-Si/a-Si:H heterojunction solar cells (Si-HJSCs) are simulated by AFORS-HET to study their performance with the back surface field (BSF) and passivation layer. Si-HJSCs(ninip) with the best open circuit voltage (Voc)(760.8 V), short circuit current density (Jsc)(36.97 mA/cm2), fill factor FF (85.22%), and efficiency (ɳ) (24.17%) were achieved. Whereas, estimated values of 675.2 mV, 33.5 mA/cm2, 83.34%, and 18.98% for a basic Si-HJSC (np) SC, which corresponds to the Voc,Jsc, FF and ɳ. The intrinsic -a-Si:H layer on both sides of the c-Si wafer has passivated the dangling bond density on the silicon, and the defect density at the interface between the c-Si and a-Si:H layers and improved the performance of Si-HJSCs. These simulation results were compared with experimental data for accuracy and validation. It was observed that the simulation results are highly promising and almost match experimental data.

Effect of Dual Intrinsic Amorphous Silicon Passivation Layers by Deposition Temperature Variation on Silicon Heterojunction Solar Cells Performance

Effect of Dual Intrinsic Amorphous Silicon Passivation Layers by Deposition Temperature Variation on Silicon Heterojunction Solar Cells Performance

Temperature and illumination dependence of silicon heterojunction solar cells with a wide range of wafer resistivities

AbstractRecently, the significant improvements in the surface and contact passivation of silicon (Si) solar cells as well as their bulk quality have shifted their operating point to higher injections. Hence, they are less dependent on wafer doping. This shift opens an opportunity of using high‐resistivity wafers for practical photovoltaic applications, introducing a promising approach to push the cell efficiency towards the intrinsic limit and to improve the module reliability by increasing the cell breakdown voltage. Therefore, insights into the performance of Si solar cells using high‐resistivity wafers at various operating temperatures are of significant interest. In this study, we investigate the temperature‐ and illumination‐dependent performance of Si heterojunction (SHJ) solar cells using a wide range of wafer resistivities (between 3 and 1000 Ω⋅cm). Although a reduction in the passivation quality of the passivating contacts is observed at elevated temperature, the impact on the temperature coefficient of the open‐circuit voltage (TCVoc)—the dominant contributor to the temperature coefficient (TC) of the cell efficiency—is very limited. Their TCVoc are still dominated by the temperature dependence of the effective intrinsic carrier concentration. Furthermore, we also find that the investigated cells are more sensitive to temperature variation at lower illumination intensities. It is noteworthy that the efficiency of the cells fabricated using high‐resistivity wafers is comparable to that of the reference cells at any given temperature, highlighting the potential of using high‐resistivity wafers for solar cells.

Precursor Molarity Influence on Sprayed Mo-doped ZnO Films for solar cells

Objectives: Current research focuses on the role of precursor molarity effect on sprayed Mo-doped ZnO films and their suitability as window layers in solar cells. Methods: Molybdenum (Mo) doped zinc oxide (MZO) thin films were deposited by the technique of spray pyrolysis, varying the Zn molarity in the range, of 0.01 M to 0.20 M at a constant substrate temperature of 400 ◦C. The Mo doping concentration was constant at 2 at. %. Findings: The XPS studies witnessed the presence of Mo and Zn in +6 and +2 state respectively. The XRD pattern showed both (111) and (002) as strong peaks, confirming the hexagonal wurtzite crystal structure. The optical investigations showed that the MZO films with Zn molarity 0.10 M exhibited high optical transmittance having a wide energy band gap. Films with zinc molarity of 0.10 M showed low resistivity and high mobility. The prepared CTS/MZO hetero junction solar cells performance was studied by evaluating parameters such as open circuit voltage (Voc) of 0.14 V, short circuit current density (Jsc) of 6.46 mA cm-2, a fill factor (FF) of 0.27, and a conversion efficiency of 0.25 %. Novelty: Studies on the physical properties of Mo:ZnO layers such as Ritveld refinement analysis and Haze were reported first time. CTS/MZO hetero junction solar cells have not yet been published. The observed results are analogous to improve the efficiency of solar cells using environmentally benign materials. Keywords: Spray pyrolysis; Thin films; XRD; Optical properties; Haze; Hall measurements

Improved n-ZnO nanorods/p-Si heterojunction solar cells with graphene incorporation

The present research explored the effect of graphene layer and zinc oxide nanorods (NRs) on the photovoltaic performance of ZnO thin film-based heterojunction solar cells. For this purpose, ZnO thin film was deposited on p-type silicon using radio frequency sputtering to serve as an anti-reflective layer and n-type semiconductor to form a heterojunction thin film solar cell. Then, a cost-effective and facile chemical bath deposition technique was employed to synthesize ZnO NRs. To study the effect of reduced graphene oxide (rGO) on the optical properties of ZnO NRs, the colloidal suspension of rGO and ZnO NRs (rGO:ZnO NRs) was prepared. The optimized nanostructures were then transferred to the surface of the ZnO/Si sample using a drop-cast method. The morphological examination of the nanostructures showed the formation of ZnO NRs with various orientations which can significantly increase the entrapment of incident photons. The XRD results indicated an improvement in the structural properties of ZnO NRs upon adding rGO flakes. The reduction of GO was confirmed using Raman spectroscopy. The higher ID/IG ratio for the rGO:ZnO NRs sample (compared to GO layers) suggested the chemical reduction of GO. The optical investigations revealed an increment in the light absorption and PL intensity in the rGO-containing samples which can be due to the role of graphene as a reinforcement phase to inhibit the electron-hole recombination. The optoelectrical properties of fabricated solar cells were investigated via the metallization of top and rear contacts to fabricate three different solar cells based on ZnO thin film, ZnO NRs, and rGO:ZnO NRs. The results showed an enhancement in the efficiency (14.12%) and the fill factor (0.552) of the solar cell based on rGO:ZnO NRs compared to the other solar cells. Therefore, the incorporation of rGO can improve the photovoltaic properties of solar cells based on ZnO nanorods.

Effect of interface properties on the performance of CGS heterojunction solar cells

"In the tandem solar cells based on CGS (ZnO/CdS/CuGaSe2) single solar cells, we have the interface state density of defects between CdS buffer layer and CuGaSe2 absorber layer witch causes undesirable carriers recombination, Gaussian distribution model describe this interfacial recombination witch depending to interface state density. In this work we simulated the effect of the interface state density in the buffer and absorber layer of ZnO/CdS/CuGaSe2 solar cells that is variated from 1014 to 1018 cm-3 on I-V characteristics and efficiency. We used the wxAMPS simulator to get the results."

Impact of oxygen partial pressure during Indium Tin Oxide sputtering on the performance of silicon heterojunction solar cells

TCO has multiple functions in SHJ solar cell design, including the lateral transport of the photogenerated current and also providing high transparency and anti-reflective behavior. While superior performance lies behind concurrently addressing its multi-functions. Hence the balance between the optical and electronic properties of TCOs need careful engineering. In this study, RF sputtered Indium Tin Oxide films are analyzed in terms of their optical and electrical properties. The variations in the resistivity, mobility, carrier concentration, and specific contact resistivity of the film concerning oxygen partial pressure are discussed. Specific contact resistivity value for screen-printed low-temperature Ag contacts is decreased down to 0.4mΩ.cm2. The total increment on short-circuit current density is 0.6 mA/cm2 by reactive ITO sputtering. The photoconversion efficiency values of SHJ cells fabricated on 170 cm2 area with reactive sputtering is 20.56%, and optical loss analysis is carried out for the SHJ solar cells to quantify the performance of solar cells.

Influence of cell edges on the performance of silicon heterojunction solar cells

Full size silicon heterojunction solar cells reach conversion efficiencies above 25%. However, photoluminescence pictures of such cells (full or cut) reveal a significant recombination activity at the cell edges. Therefore, mitigating recombination at the edges can in principle represent an interesting path to unlock higher cell efficiencies. This challenge is all the more important for cells with a high perimeter/area ratio, as achieved through the cutting of full size cells. For such technologies, the edges resulting from cutting are cleaved while the remaining edges typically feature a gap where TCO is missing to avoid front to back short-circuit. In this paper, we specify the physical mechanisms involved in the edge-induced performance losses for SHJ cells. In light of these results, we provide guidelines for the mitigation of such losses at the full-size and cut cells scale for M6 to M12 sizes such as the reduction of the TCO-free region and the c-Si bulk resistivity. Having a closer look at cut cells, we calculate the cell performance as a function of its size (from half-to sixth-cell), the size of its mother cell (from M6 to M12) and the passivation quality of the cut-edges. Our results emphasize on the interest to develop suitable repassivation schemes for cut cells to improve or even surpass the efficiency of the mother cell.

Improved conversion efficiency of p-type BaSi2/n-type crystalline Si heterojunction solar cells by a low growth rate deposition of BaSi2

The effect of low growth rate deposition (LGD) of BaSi2 on the film quality and performance of silicon heterojunction solar cells was investigated. The total thickness of the BaSi2 layer decreased with increasing LGD duration (tLGD). Analysis using Raman spectroscopy indicated that an amorphous Si (a-Si) phase existed on the surface of the BaSi2 layer. The a-Si on the surface was converted into BaSi2 by post-annealing owing to the diffusion of Ba and Si atoms. X-ray diffraction analysis revealed that LGD improved the rate of a-axis orientation and crystallinity. Post-annealing was also observed to have significantly improved these structural properties. Furthermore, the solar cell performance was observed to be strongly dependent on tLGD, and the highest conversion efficiency of 10.62% was achieved by the p-BaSi2/n-c-Si heterojunction solar cells at a tLGD of 6 min. The improved structure and solar cell properties are attributed to improved atom rearrangement during LGD.

Simulation of the performance of organic solar cells based on D1-BT-EDOT-BT-D2-A/PCBM structures

The analysis of microelectronic and photonic structures-one dimension (AMPS-1D) was used to study and simulate the performance of organic heterojunction solar cells based on D1 –B-Edot-B-D2-A as electron donors, and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor. The organic photovoltaic cell devices using T3-B-Edot-B-T3-A/PCBM showed the improved open-circuit voltage Voc, short-circuit current density Jsc, fill factor FF, and power conversion efficiency PCE values for the optimum thickness of 120 nm and the effective state density of electrons and holes of 1021cm−3.The P3-B-Edot-B-T3-A/PCBM and P3-B-Edot-B-P3-A/PCBM based devices exhibited a power conversion efficiency (PCE) of 9.295% and 8.735%, respectively, which outperformed the corresponding T3-B-Edot-B-T3-A/PCBM, Cbz-B-Edot-B-T3-A/PCBM, F-B-Edot-B-T3-A/PCBM, and A-B-Edot-B-T3-A/PCBM based devices (7.330, 6.622, 7.226, and 7.327%). More importantly, the P3-B-Edot-B-T3-A/PCBM and P3-B-Edot-B-P3-A/PCBM -based device delivered the highest PCE of 14.432% and 15.031% respectively, when we deposit a layer of PEDOT between the indium tin oxide (ITO) and the active layer, which is a clear improvement over other results in the literature.

Optimization of Mo/Cu(In, Ga)Se2/CdS/ZnO Hetero-Junction Solar Cell Performance by Numerical Simulation with SCAPS-1D

Optimization of Mo/Cu(In, Ga)Se2/CdS/ZnO Hetero-Junction Solar Cell Performance by Numerical Simulation with SCAPS-1D

Temperature‐dependent performance of silicon heterojunction solar cells with transition‐metal‐oxide‐based selective contacts

AbstractThe temperature coefficient (TC) is an essential figure of merit to accurately evaluate solar cell performance at various operating temperatures and hence enabling the comparison between different cell technologies. Recently, solar cells that use passivating contacts based on transition metal oxide (TMO) layers have attracted much attention due to their excellent performance. Therefore, knowledge of their TCs and insights into their performance at various operating temperatures are of significant interest. In this study, we investigate the temperature‐dependent performance of solar cells with TMO‐based passivating contacts at various illumination intensities. We then compare their performance to that of standard silicon heterojunction (SHJ) solar cells. The efficiency TC (TCη) of solar cells that use passivating contacts based on molybdenum oxide (MoOx) and titanium oxide (TiOx) films is found to be almost identical. Both outperform the TCη of the standard SHJ cells and are greatly superior to those of cell structures without passivating contacts. The superior TCη of the MoOx‐based cells is mainly due to their favourable TCs of the short‐circuit current density (TCJsc) and fill factor (TCFF), whereas the superiority of TCη of the TiOx‐based cells is solely resulting from the superior TCFF. The favourable TCJsc of the MoOx‐based cells is explained by an enhanced spectral response at short wavelengths with increasing temperature, due to the improvement of the passivation quality of the MoOx‐based passivating contacts. The beneficial TCFF of both solar cells is partly resulting from the improvement of the contact resistivity of the TMO‐based passivating contacts which counterbalances some of the fill factor losses at elevated temperatures. Although an improvement of the passivation quality of the TMO‐based passivating contacts is observed at elevated temperature, it does not have a strong impact on the TC of the open‐circuit voltage of the investigated solar cells. Furthermore, we also found that the studied cells are less sensitive to temperature variation at higher illumination intensities.