Crystalline Silicon Heterojunction Solar Cells Research Articles

Bifacial silicon heterojunction solar cells using transparent‐conductive‐oxide‐ and dopant‐free electron‐selective contacts

AbstractThe development of transparent electron‐selective contacts for dopant‐free carrier‐selective crystalline silicon (c‐Si) heterojunction (SHJ) solar cells plays an important role in achieving high short‐circuit current density (JSC) and consequently high photoelectric conversion efficiencies (PCEs). This becomes even more important when focusing on the development of bifacial solar cells. In this study, bifacial SHJ solar cells using a transparent‐conductive‐oxide‐free and dopant‐free electron‐selective passivating contacts are developed, showing a JSC bifaciality of up to 97%. Intrinsic ZnOX layer deposited by atomic layer deposition was used in this structure, which simultaneously provides negligible passivation loss after annealing and enables a low contact resistivity on the electron‐selective contact. With both side finger metal electrodes contact, this bifacial solar cell shows an efficiency of 21.2% under front‐side irradiation and 20.4% under rear‐side irradiation, resulting in an estimated output power density of 24.1 mW/cm2 when considering rear‐side irradiance of 0.15 sun.

Highly Efficient and Highly Flexible Thin Crystalline Silicon Heterojunction Solar Cells Based on Dopant-Free Carrier-Selective Contacts Fabricated with Simple Processes

Highly Efficient and Highly Flexible Thin Crystalline Silicon Heterojunction Solar Cells Based on Dopant-Free Carrier-Selective Contacts Fabricated with Simple Processes

A novel silver-doped nickel oxide hole-selective contact for crystalline silicon heterojunction solar cells

A novel silver-doped nickel oxide hole-selective contact for crystalline silicon heterojunction solar cells

Exceptional Hole-Selective Properties of Ta2O5 Films via Sn4+ Doping for High Performance Silicon Heterojunction Solar Cells.

Carrier-selective passivating contacts using transition metal oxides (TMOs) have attracted great attention for crystalline silicon (c-Si) heterojunction solar cells recently. Among them, tantalum oxide (Ta2O5) exhibits outstanding advantages, such as a wide bandgap, good surface passivation, and a small conduction band offset with c-Si, which is typically used as an electron-selective contact layer. Interestingly, it is first demonstrated that solution-processed Ta2O5 films exhibit a high hole selectivity, which blocks electrons and promotes hole transport simultaneously. Through the ozone pre-treatment of Ta2O5/p-Si interface and optimization of the film thickness (≈9nm), the interfacial recombination is suppressed and the contact resistivity is reduced from 178.0 to 29.3mΩcm2. Moreover, the Sn4+ doping increases both the work function and oxygen vacancies of the film, contributing to the improved hole-selective contact performance. As a result, the photoelectric conversion efficiencies of Ta2O5/p-Si heterojunction solar cells are significantly improved from 14.84% to 18.47%, with a high thermal stability up to 300°C. The work has provided a feasible strategy to explore new features of TMOs for carrier-selective contact applications, that is, bipolar carrier transport properties.

Optical, Electrical and Structural Properties of ITO/IZO and IZO/ITO Multilayer Transparent Conductive Oxide Films Deposited via Radiofrequency Magnetron Sputtering

In this study, we investigated the potential of multilayer TCO structures, specifically those made up of Indium Tin Oxide (ITO) and Indium Zinc Oxide (IZO), for crystalline silicon heterojunction solar cells (SHJ). We used the radiofrequency (RF) magnetron sputtering method to deposit various thin-film structures under various deposition temperatures and evaluated their electrical, optical, and morphological properties. The objective was to obtain films with lower sheet resistances and higher transmittances than those of single-layer thin films. Our results show that the ITO/IZO/ITO/IZO/ITO multilayer film structure deposited at 200 °C achieves the best sheet resistance of 18.5 Ohm/sq and a high optical transmittance of over 90% at a 550 nm wavelength. This indicates that multilayer TCO structures have the potential to be more optically and electrically efficient, and that they can improve the performance of optoelectronic devices. Finally, a power conversion efficiency of 17.46% was obtained for a silicon heterojunction (SHJ) solar cell fabricated using an ITO/IZO/ITO/IZO/ITO multilayer film structure deposited at 200 °C as a front TCO. Our study provides valuable insights into the field of TCOs and offers a promising avenue for future research.

Beyond 25% efficient crystalline silicon heterojunction solar cells with hydrogenated amorphous silicon oxide stacked passivation layers for rear emitter

Hydrogenated amorphous silicon oxide (a-SiOx:H) alloy is considered as a promising alternative to hydrogenated amorphous silicon (a-Si:H) in crystalline silicon heterojunction (SHJ) solar cells due to its reduced parasitic absorption induced by the incorporation of oxygen. However, the large valence band offset (ΔEV) between a-SiOx:H and crystalline silicon (c-Si) usually leads to low fill factor (FF) for the solar cells. Here, we designed a trilyer a-SiOx:H(i) stacked passivation scheme underneath the rear emitter (p) for the SHJ solar cell on n-type c-Si wafer via depositing the a-SiOx:H(i) layers with different oxygen contents by plasma-enhanced chemical vapor deposition (PECVD). Highly efficient SHJ solar cells with the average efficiency of 25.37% were obtained by optimizing the trilayer a-SiOx:H(i) passivation structure with an oxygen-rich layer inserted between two oxygen-less layers. Comparing to the solar cells with complete a-Si:H passivation layers, higher short-circuit current density (JSC) and open-circuit voltage (VOC) of the solar cells were achieved, which indicated excellent passivation and low parasitic absorption contributed from the a-SiOx:H(i) stacked layers. At the same time, FF of the solar cells was also increased slightly. The corresponding improvement mechanisms were analyzed carefully. As a demonstration, the highest efficiency of the SHJ solar cells passivated by the trilayer a-SiOx:H(i) scheme for rear emitter was up to 25.44%.

Tunable Hole‐Selective Transport by Solution‐Processed MoO3−x Via Doping for p‐Type Crystalline Silicon Solar Cells

Molybdenum oxide (MoO3−x, x < 3) has been successfully used as an efficient hole‐selective contact material for crystalline silicon heterojunction solar cells. The carrier transport capability strongly depends on its work function, that is, oxygen vacancies; however, there are lack of effective methods to modulate the multiple oxidation states. Herein, the oxidation states of solution‐processed MoO3−x by doping Nb5+ to improve its hole‐selective contact performance with silicon are tuned. With the optimum doping concentration of 5%, both the reduced Mo5+ and oxygen vacancies increase, resulting in a decrease in the contact resistivity between the MoO3−x film and p‐type silicon from 161.1 to 62.9 mΩ·cm2 and an increase of the effective carrier lifetime from 165.4 to 391.0 μs simultaneously. Similarly, the doping of Ta5+ or V5+ in MoO3−x improves the passivated contact performance with silicon, while the former increases the concentration of oxygen vacancies and the latter reduces it. The solar cell with the structure of Ag/MoO3−x:Nb/p‐Si exhibits a conversion efficiency of 18.37%, which is the highest so far reported for the solution‐processed MoO3−x/silicon heterojunction. This work demonstrates a feasible strategy of tuning hole selectivity in MoO3−x by doping for high‐efficiency solar cells and other optoelectronic device applications.

Monolithic perovskite/silicon tandem solar cells with optimized front zinc doped indium oxides and industrial textured silicon heterojunction solar cells

The power conversion efficiency (PCE) of monolithic perovskite/silicon tandem solar cells has surpassed that of silicon single-junction solar cells recently. Industrial textured crystalline silicon heterojunction solar cells are considered as competitive candidate bottom cells because of their high efficiency and simple process flow. Meanwhile, the front transparent conductive window layers with industrial compatibility and low processing temperature are worth investigating in detail. In this work, zinc-doped indium oxide (IZO) thin films achieved by room-temperature sputtering are studied as a function of sputtering powers. The IZO thin film with the resistivity and electron mobility of 7.2 × 10−4 Ω cm and 40.03 cm2/Vs are obtained under 85 W, which is implemented into the monolithic perovskite/silicon tandem solar cells. A PCE of 19.38% is realized based on the industrial textured silicon heterojunction bottom solar cell and optimized IZO films.

Optimization of the Electrode Formation Mechanism for Crystalline Silicon Heterojunction Solar Cells

The screen-printing process for making good contact of electrodes with the top layer of solar cells is crucial for enhancing the electrical properties of a solar cell. This paper reports the experimental approach adopted for the process of electrode formation and the resulting shape of electrodes in silicon-based heterojunction (SHJ) solar cells. It was observed that good contact between electrodes and the top transparent conductive oxide (TCO) layer strongly depends on the squeegee pressure, curing temperature, and curing time. By optimizing the squeegee pressure at 0.350 MPa, snap-off distance of 1.4 mm, squeegee speed of 80 mm sec−1, curing temperature of 180 °C, and curing time of 30 min, respectively for which the height to width ratio (aspect ratio) of the fabricated electrodes was achieved around 0.66. The results have been verified through 3D laser profiler, field emission scanning electron microscopy (FE-SEM), transfer length method (TLM), and Light current-voltage (LIV) measurements. The SHJ solar cells were fabricated using an optimized condition and successfully achieved splendid properties of short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), and efficiency (η) up to 40.57 mA cm−2, 723 mV, 81.03%, and 23.79%, respectively.

HAXPESによる結晶シリコンヘテロ接合型太陽電池の課題解明

HAXPESによる結晶シリコンヘテロ接合型太陽電池の課題解明

Enabling Transparent‐Conductive‐Oxide Free Efficient Heterojunction Solar Cells by Flexibly Using Dopant‐Free Contact

AbstractMinimizing the optical parasitic absorption loss in hydrogenated amorphous silicon (a‐Si:H) and transparent conductive oxide (TCO) layers is considered an effective approach to further improve the power conversion efficiencies (PCEs) of crystalline silicon heterojunction (SHJ) solar cells. In this work, carrier‐selective passivating contacts for both polarities, e.g., alkali fluoride/aluminum electron‐selective contact and transition metal oxide/silver hole‐selective contact, are used to completely replace the doped a‐Si:H layers in SHJ solar cell, forming a totally TCO‐ and dopant‐free asymmetric structure. By minimizing the charge carrier transporting and recombination losses on the front‐side electron‐selective contact through interface engineering, an improved photovoltaic performance with a short‐circuit current density of 40.5 mA cm−2, an open‐circuit voltage of 0.709 V, and a fill factor of 79.6% is realized, resulting in a final PCE exceeding 22.9%. The successful demonstration of this work provides an effective way to further boost the efficiency, as well as reduce the cost of SHJ solar cells with a TCO‐free and doped a‐Si:H‐free configuration, using a moderate and simplified fabrication process.

Greatly enhanced hole collection of MoO x with top sub-10 nm thick silver films for gridless and flexible crystalline silicon heterojunction solar cells.

Greatly enhanced hole collection of MoOx is demonstrated experimentally with a top sub-10 nm thick Ag film, allowing for an efficient dopant-free contacted crystalline silicon (c-Si) heterojunction solar cell without a front grid electrode. With the removal of shadows induced by the front grid electrode, the gridless solar cell with the MoOx/Ag hole-selective contact (HSC) shows an increment of ∼8% in its power conversion efficiency (PCE) due to the greatly improved short-circuit current density (Jsc) as well as the almost undiminished fill factor (FF) and open-circuit voltage (Voc), while the gridless solar cells with the conventional MoOx/ITO and pure MoOx HSCs exhibit ∼20% and ∼43% degradations in PCE due to the overwhelming decrease in their FF and Jsc, respectively. Through systematic characterizations and analyses, it is found that the ultrathin Ag film (more conductive than ITO) provides an additional channel for photogenerated holes to transport on MoOx, contributing to the great enhancement in the hole collection and the great suppression of the shunt loss in the gridless solar cells. A 50 μm thick gridless c-Si heterojunction solar cell with the MoOx/Ag HSC is 75% thinner but is 86% efficient compared to its 200 μm thick counterpart (while the 50 μm thick gridless solar cell with the MoOx/ITO HSC is much less efficient). It is over 82% efficient after being bent to a curvature radius as small as 4 mm, also showing superior mechanical flexibility to its counterpart with the MoOx/ITO HSC. Our MoOx/Ag double-layer HSC can be easily fabricated through thermal evaporation without breaking the vacuum, saving both the time and cost of the fabrication of the whole device. Therefore, this work provides a guide for the design of efficient HSCs for high-efficiency, low-cost, and flexible solar cells.

Optimization of indium recovery from waste crystalline silicon heterojunction solar cells by acid leaching

Recovery of rare metal indium from waste crystalline silicon heterojunction (HJT) solar cells is important with the large-scale development of photovoltaic industry, is becoming economically and environmentally justified. Thus, the objective of this work is to study hydrometallurgical recovery of indium and valuable materials from HJT solar cells. In addition, to study some parameters used in this process. In this study, three key processes including pretreatment, acid leaching and optimization design on singer-factor to minimize waste of resources were proposed and implemented. Firstly, the samples were characterized by Inductively coupled plasma optical emission spectrometer (ICP-OES) showed indium concentrations of 2950 mg/kg. Then, reacting with NaOH 10% at 90 °C for 8 min can separate the silver electrodes on the surface of the cells, which realize the primary recovery of the silver electrode. After this, the influence of acid type, acid concentration, retention time and temperature on indium leaching was analyzed. Subsequently, the BBD method under response surface methodology was used to optimize the leaching rate. Optimum operating conditions include a leaching step for 148 min at 93.2 °C in the presence of H 2 SO 4 6 mol/L with extraction rate of 95.2% and validate the feasibility with determination coefficient (99.55%) of the RSM model. • A novel experimental method is proposed for recovering indium from waste crystalline silicon heterojunction (HJT) solar cells. • A process to recovery of valuable materials in the HJT cells is designed. • Optimization of indium recovery by using Response Surface Model (RSM).

Effect of Thermal Annealing on the Charge Carrier Selectivity of Ultra‐Thin Organic Interface Dipoles in Silicon Organic Heterojunction Solar Cells

Interfacial layers consisting of organic molecules with a permanent dipole moment exhibit enhanced charge carrier selectivity when applied as electron‐selective contacts in crystalline silicon (c‐Si) heterojunction solar cells. It is found that thermal annealing has a detrimental effect on the charge carrier selectivity of dipole materials based on the amino acid l‐histidine mixed with a fluorosurfactant. Although, the implied open‐circuit voltage (iVoc) increases with annealing, the Voc decreases significantly which is accompanied by a decrease in the built‐in voltage (Vbi) and increase in the specific contact resistivity (ρc). Based on numerical device simulations, it is concluded that the tunneling of electrons through the dipole layer becomes less effective with increasing annealing temperature due to the decomposition of the dipole materials. The decomposition leads to a more “resistive” interfacial layer and to a gradient in the electron quasi‐Fermi potential and, thus, a decrease in Voc. Furthermore, storage under ambient air at room temperature degraded the electron‐selective contacts substantially, limiting the potential of the dipole material for the application in silicon organic heterojunction solar cells.

Transparent-conductive-oxide-free front contacts for high-efficiency silicon heterojunction solar cells

<h2>Summary</h2> In order to compensate the insufficient conductance of heterojunction thin films, transparent conductive oxides (TCO) have been used for decades in both sides of contacted crystalline silicon heterojunction (SHJ) solar cells to provide lateral conduction for carrier collection. In this work, we substitute the TCO layers by utilizing the lateral conduction of c-Si absorber, thereby enabling a TCO-free design for SHJ solar cells achieving a low series resistivity of 0.32 Ωcm² and a good fill factor of 80.7% with a conventional finger pitch of 1.8 mm. Achieving high efficiencies in TCO-free SHJ solar cells requires suppressing deterioration of the passivation quality induced by the direct metal-to-a-Si:H contacts. We show that an ozone treatment at the a-Si:H/metal interface suppresses the metal diffusion into the a-Si:H layer and improves the passivation without increasing the contact resistivity. SHJ solar cells with TCO-free front contacts and ozone treatment achieve efficiencies of >22%.

Device design for high‐efficiency monolithic two‐terminal, four‐terminal mechanically stacked, and four‐terminal optically coupled perovskite‐silicon tandem solar cells

A device based on perovskite and silicon tandem solar cells is considered as an interesting route to improve cell efficiency further the limit of single junction by keeping the reasonable cost of production. Here, we assess the device performances of CH3NH3PbI3 perovskite as top sub-cells in tandem solar cells in association with traditional crystalline silicon heterojunction solar cells of various configurations such as monolithic two terminals, four terminals mechanically stacked, and four-terminal optically coupled perovskite/Si tandem solar cells. Our simulation findings highlight that the suggested architecture design increases the device performance by optimizing the thickness of perovskite. Furthermore, the optimal doping concentration of perovskite (1018 cm−3) has contributed to achieve high tandem efficiencies of various device configurations.

Development of indium tin oxide stack layer using oxygen and argon gas mixture for crystalline silicon heterojunction solar cells

Indium tin oxide (ITO) films were used as transparent conductive oxide (TCO) layers in crystalline silicon heterojunction (c-Si-HJ) solar cells. An ITO film was deposited by radio frequency (RF) magnetron sputtering with the oxygen-argon (O2–Ar) gas mixture. The increasing of the O2/Ar ratio in ITO film deposition resulted in the improvement of transmittance and short circuit current density (Jsc) of c-Si-HJ solar cells, while film electrical property, fill factor (FF) and efficiency (η) of the solar cell were decreased. The enhancement of the Jsc and FF caused by the ITO stack layer on the efficiency of the c-Si-HJ solar cell was investigated. The c-Si-HJ solar cells using an ITO stack layer have a high photovoltaic (PV) parameter compared to conventional ITO (Ar gas) and ITO (O2–Ar gas mixture) layer. By using an ITO stack layer for a c-Si-HJ solar cell, the efficiency achieved was as high as 18.4%. (Voc = 702 mV, Jsc = 34.8 mA/cm2, FF = 0.75).

Effect of forming gas annealing on hydrogen content and surface morphology of titanium oxide coated crystalline silicon heterocontacts

Crystalline silicon (c-Si) heterojunction solar cells using carrier-selective contacts have drawn considerable attention due to their high power conversion efficiency with a simple fabrication process. Titanium oxide (TiOx) is one of the most promising materials that can provide excellent surface passivation as well as carrier-selective transport. In this study, the authors fabricate the TiOx/SiOx/c-Si heterocontacts by atomic layer deposition (ALD) and investigate the effect of the forming gas annealing (FGA) on hydrogen content and surface morphology by utilizing nuclear reaction analysis (NRA) and atomic force microscope (AFM) measurements, respectively. The highest effective carrier lifetime (τeff) of 891 μs is realized for TiOx/SiOx/c-Si heterocontacts after FGA at 400 °C for 3 min, indicating that high surface passivation performance is obtained. NRA clarifies that the hydrogen content in the TiOx/SiOx/c-Si heterocontacts decreases with increasing FGA temperature and duration. With increasing FGA temperature and duration, also the surfaces of the TiOx/SiOx/c-Si heterocontacts are roughened, which means enhanced crystallization of the TiOx/SiOx/c-Si heterocontacts. From the NRA and AFM analyses, the authors conclude that there is a trade-off relationship between the hydrogen content in the TiOx/SiOx/c-Si heterocontacts and the crystallization of the TiOx layers.

Analysis of Process‐Dependent Electrical Properties of Silicon Heterojunction Solar Cells by Quantum Efficiency and Temperature‐Dependent Current Density–Voltage Measurements

Amorphous silicon–crystalline silicon (a‐Si:H/c‐Si) heterojunction solar cells are fabricated by infrared (IR) radiative or resistive preheating of silicon wafers before the a‐Si:H layers deposition. The cells with IR radiative or resistive preheating lead to without S‐shape (WoS) or with S‐shape (WS) in their light current density–voltage (J–V) characteristics, respectively. The Suns‐Voc analysis shows no front/back metal contact barriers for minority carriers in both cells. The light‐ and voltage‐bias‐dependent quantum efficiencies of the WS cell show the hindrance of carrier collection at the a‐Si:H/c‐Si interface due to the band offset, whereas more defective a‐Si:H layers are observed in the WoS cell. The WS and WoS cells' temperature‐dependent dark J–V characteristics reveal that the carrier transport is through tunnel‐assisted recombination and tunneling, respectively. The IR preheating of wafers results in the reduction of the bandgap of a‐Si:H and facilitates for minimizing the band offset at the interface, whereas, the resistive heating shows the relatively better a‐Si:H/c‐Si interface passivation.

Interfacial engineering to boost photoresponse performance and stability of V2O5/n-Si heterojunction photodetectors

Transitional metal oxides (TMOs) have demonstrated as a promising alternative to doped layers in high-efficient crystalline silicon heterojunction solar cells. However, the unintentional oxidation causes serious carrier recombination at the interface, which accounts for the low photoelectric conversion efficiency and poor stability. Herein, a self-powered, broad-band, fast-response V2O5/n-Si heterojunction photodetectors (PDs) are fabricated by thermal evaporation of an ultrathin V2O5 thin films on nanoporous pyramid silicon structures. By interfacial engineering with structural optimization and surface methyl passivation, the photodetection performance and stability of V2O5/n-Si PDs can be significantly enhanced. The V2O5/n-Si heterojunction PDs demonstrate a high on/off ratio of 1.4×104, fast-response speed of 9.5 μs, high responsivity of 185 mA W−1 (@940 nm) and high specific detectivity (1.34×1012 Jones). Based on the energy band alignment analysis, the excellent photoresponse performance is mainly attributed to the efficient carrier separation after surface passivation by methyl group. Additionally, the built-in electric field at the interface also accelerates the charge carrier separation. Our work would contribute to the fabrications of other TMOs-based heterojunctions, and give some enlightening insights into the understanding of carrier transportation in heterojunctions.