Silicon Heterojunction Solar Cells Research Articles

Improving Solar Cell Efficiency of Silicon and Silicon Tandem Structure by Using Surface Modification

Silicon heterojunction (SHJ) solar cells face challenges in maximizing energy capture due to limitations in light collection and surface passivation. To address this, the use of SHJ tandem solar cells in a back‐to‐back configuration is explored, allowing illumination from both sides to enhance light absorption and energy generation. This study aims to improve the stability and efficiency of these cells through Al2O3 and Nafion surface treatments. Al2O3 is deposited to enhance bifacial light collection, while Nafion is applied for surface passivation to increase the fill factor (FF). The method involves adding 0.1–0.6 units of incident light to the rear of the cells to evaluate the effects of these treatments. The results show a 2.06% increase in efficiency with Al2O3 and a 1.72% improvement with Nafion under standard illumination conditions. The optimized tandem SHJ with Al2O3 and Nafion achieves a Jsc of 62.01 mA cm−2, Voc of 650.63 mV, FF of 76.49%, and an efficiency of 30.86%. These findings demonstrate the significant potential of these surface treatments to enhance the overall performance of bifacial back‐to‐back tandem SHJ solar cells.

Self-Diffusion Effect Assisted TiO2/Li3PO4 Electron Selective Passivating Contact in Silicon Solar Cells Approaching 23% Efficiency.

Carrier selective contacts with passivation effects are considered to have a significant influence on the performance of crystalline silicon (c-Si) solar cells. It is essential for electron selective contact materials to meet the requirements of ultra-low contact resistance and excellent passivation effects. This work introduces a stack layer of Lithium Phosphate (Li3PO4) /Titanium Dioxide (TiO2) as a new electron selective passivating contact. It is found that the stack achieves an impressive contact resistivity (ρc) of 0.128mΩcm2 on n-type c-Si substrates with resistivity ranging from 1 to 3Ωcm (14.6mΩcm2 for the n-Si/a-Si:H/Li3PO4/TiO2/Al contact). Furthermore, it effectively reduces the surface recombination parameter (J0) to less than 4fA by incorporating a 6nm a-Si:H(i) layer. The characterization of the n-Si/Li3PO4/TiO2 interface reveals that phosphorus diffusion into silicon plays a crucial role in achieving the ultra-low contact resistivity, while the presence of PO4 3- groups helps in fixing hydrogen atoms to maintain the desired chemical passivation effect. Finally, a silicon heterojunction solar cell (SHJ) with a rear full-area configuration of a-Si:H/Li3PO4/TiO2/Al is successfully demonstrated achieving an impressive power conversion efficiency of 22.89%. The result proves the efficacy of employing hydrogen-rich low-work function metal oxide stacks as electron selective passivating contacts.

Solution-Processed Fabrication of Ni3S2-Based Nanoheterostructure on Silicon Heterojunction Photocathode for Boosting Solar Hydrogen Generation.

Silicon heterojunction (SHJ) solar cell is an advanced and mature photovoltaic cell. Development of photoelectrochemical (PEC) water splitting devices for hydrogen fuel production using SHJ solar cells is considered as a promising approach to address energy crisis. To achieve this goal, it is necessary to deposit passivation layer and cocatalyst layer on the photoelectrode. However, the development of low-cost and scalable preparation methods for high-quality passivation and cocatalyst layer continues to be a significant challenge. Herein, an efficient passivation layer and hydrogen evolution reaction (HER) catalyst are successfully fabricated via solution processed methods. To improve the HER activity of Ni3S2, a Ni3S2-based nanoheterostructure of crystalline Ni3S2, Ni, and amorphous Y(OH)3 is constructed. The optimized photocathode exhibits excellent PEC-HER performance, which achieves a saturated photocurrent of -35.5mA cm-2 and an applied bias photon-to-current efficiency (ABPE) of 8.4 ±0.1% under simulated AM1.5G one-sun illumination and more than 120h of continuous water splitting. This study paves a way for the design and large-scale manufacturing of cost-efficient SHJ photocathode devices.

Highly Transparent Conductive Gallium-Doped Zinc Oxide Thin Films Grown by Reactive Plasma Deposition for Silicon Heterojunction Solar Cells

Highly Transparent Conductive Gallium-Doped Zinc Oxide Thin Films Grown by Reactive Plasma Deposition for Silicon Heterojunction Solar Cells

Using phosphorus doped hydrogenated silicon oxycarbide film as a window layer on the light entrance side of silicon heterojunction solar cells: The role of phase separation on electron transport

The phosphorus doped hydrogenated nanocrystalline silicon oxycarbide (n-nc-SiCO:H) layer can be used as a window layer on the light incident side of silicon heterojunction solar cells (HJT). The chemical composition, structural organization and properties of the n-nc-SiCO:H layer deposited from plasma enhanced chemical vapor deposition (PECVD) method can be easily manipulated via radio frequency power density tuned. Phase separation is observed in the n-nc-SiCO:H layer in which nanoscale silicon crystallites were embedded in amorphous silicon oxycarbide matrix. The optical properties of the n-nc-SiCO:H layer are depended on oxygen and carbon atoms incorporation ratio. The conductivity of the n-nc-SiCO:H layer is dominated by activated phosphorus concentration and the phase separation. The activated phosphorus atoms which play an important role on electron transportation are distributed in both crystalline silicon phase and amorphous silicon phase. Both activated phosphorus concentration and band gap value for oxygen rich amorphous silicon oxycarbide layer are determined by incorporation ratio of O atoms. The interplay effects of optical and electrical properties of the n-nc-SiCO:H layers on HJT cells electric performance variation are revealed out in this report. An average efficiency (across ∼120 cells) of 26.3 % was achieved in cells with optimized power density for the n-nc-SiCO:H layer. The results demonstrate that phase separation in the n-nc-SiCO:H layer plays a critical role on electron transportation.

Downshifting Encapsulant: Optical Simulation Evaluation of the Solution to Ultraviolet‐Induced Degradation in Silicon Heterojunction Solar Cells

Ultraviolet (UV)‐induced degradation (UVID) poses a significant challenge for the prospective mass production of silicon heterojunction (SHJ) solar cells, known for their high efficiency. In this study, the magnified impact of UV radiation when employing a silicon carbide (SiC)‐based transparent passivating contact (TPC) on the front side of SHJ solar cells is reported. A reduction in open‐circuit voltage (VOC), short‐circuit current (JSC), and fill factor of 12%, 6%, and 11%, respectively, is observed after UV exposure. Conventional UVID mitigation measures, UV‐blocking encapsulation, are assessed through single‐cell TPC laminates, revealing an unavoidable tradeoff between current loss and UVID. Alternatively, the utilization of ultraviolet‐downshifting (UV‐DS) encapsulants is proposed to convert UV radiation into the visible light spectrum. An optical simulation method, conducted via OPAL2, is presented to evaluate UV‐DS encapsulants for diminishing UVID in SHJ solar cells with different front contacts. A simple methodology is proposed to mimic the optical property of UV‐DS encapsulants. In the simulation results, additional current gains of up to 0.33 mA cm−2 achievable with suitable UV‐DS encapsulants are highlighted. The factors related to the UV‐DS effects are evaluated and the optimization pathway for UV‐DS encapsulants is elucidated.

Metallization process optimization of HIT solar cell for high current density and silver reduction

The Silicon heterojunction (SHJ) solar cell belongs to the most viable cell structure that enables low cost as well as high efficiency. For SHJ cells, silver (Ag) paste has been used through screen-printed process that is hardenable at low temperature. The procedure of screen printing is essential for improving the electrical properties because it allows electrodes to make good contact with the top layer of solar cells. This paper describes the experimental procedure to optimize the process condition for achieving comparatively high efficiency with minimum usage of Ag consumption. It was noticed that adequate contact among electrodes and uppermost transparent conductive oxide layer in SHJ solar cell depending considerably on squeeze speed, squeegee pressure, scraper speed, curing time and temperature. By controlling the snap-off distance of 1.4 mm, squeegee pressure at 0.3 MPa, scraper speed of 10 mm/sec, squeegee speed of 170 mm/sec, curing time of 20 min and curing temperature of 190 °C respectively, we achieved comparatively high efficiency of 22.46 %.

Interface properties study of black silicon solar cells with front surface a-Si:H/c-Si heterojunction

Abstract The exceptionally low reflectance of black silicon (Si) across a broad wavelength range makes it an intriguing surface texture for solar cell applications. Si heterojunction (SHJ) solar cells fabricated on black Si formed by dry reactive ion etching using inductive coupled plasma on n-type Si are explored. The study is focused on the properties of the a-Si:H/ crystalline silicon interface, being a key issue for the photovoltaic performance of SHJ. Deep-level transient spectroscopy detected no radiation defect in Si after the etching. The surface of black Si was passivated with an intrinsic a-Si:H layer, followed by the deposition of p-type and n-type a-Si:H on the front and back sides, respectively. The SHJ solar cell photovoltaic performance based on black Si is strongly influenced by defect density at the a-Si:H/Si interface. Admittance spectroscopy and effective charge carrier lifetime measurements demonstrate that interface defect density decreases with the increase of (i) a-Si:H thickness. The value of 0.75 ms effective charge carrier lifetime was reached for single (i) a-Si:H layer passivation and 0.25 ms when (p)a-Si:H was deposited over the intrinsic a-Si:H layer. The measured open circuit voltage values for the SHJ solar cells increase with the (i) a-Si:H layer thickness reaching 658 mV. However, the fill factor decreases with increasing (i) a-Si:H layer thickness, limiting the efficiency at the maximum value below 14% due to the thickness uniformity of the a-Si:H layer. The development of conformal growth of a-Si:H is a key issue for further improvement of black Si heterojunction solar cell photovoltaic performance.

Interpretation of the degradation and trends in the performance of heterojunction silicon solar cells at low temperature

A compact model that combines numerical simulations using AFORS-HET and accurate equivalent circuit modelling is proposed and used to interpret the origins of the degradation and anomality's in the performance of the a-Si:H/c-Si heterojunction solar cells and its parameters at low temperature. The interpretations are applied to several trends reported on real cells. It is shown that as T decreases the a-Si:H(i) layer is depleted gradually from holes and that the cell operation fails once the layer is totally depleted and becoming intrinsic. The failure is caused by a substantial and sharp increase in the cell series resistance causing the collapse of the fill factor and of the cell current. It is found that at low temperature the open circuit voltage is significantly affected and its temperature dependence strongly distorted by hole depletion in the a-Si:H(i) spacer especially when the TCO work function is not appropriate. It is aslo shown that the S-shape in the cell I-V characteristics under illumination is closely linked to the TCO barrier reverse saturation current which explains its higher probability of appearnce at low temperature. Finally, it is concluded that the HJT cell would perform optimally down to the low 200 K range when the a-Si:H(p) is heavily doped and the front contact is ideally ohmic. Failing to satisfy such conditions the temperature range in which the HJT cell is useful is very limited.

Perovskite/Silicon Tandem Solar Cells Above 30% Conversion Efficiency on Submicron-Sized Textured Czochralski-Silicon Bottom Cells with Improved Hole-Transport Layers.

In perovskite/silicon tandem solar cells, the utilization of silicon heterojunction (SHJ) solar cells as bottom cells is one of the most promising concepts. Here, we present optimization strategies for the top cell processing and their integration into SHJ bottom cells based on industrial Czochralski (Cz)-Si wafers of 140 μm thickness. We show that combining the self-assembled monolayer [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) with an additional phosphonic acid (PA) with different functional groups, can improve film formation when used as a hole transport layer improving wettability, minimizing shunt fraction and reducing nonradiative losses at the buried interface. Transient surface photovoltage and transient photoluminescence measurements confirm that the combined Me-4PACz/PA layer has similar charge transport properties to Me-4PACz alone. Moreover, this work demonstrates the potential for thin, double-side submicron-sized textured industry-relevant silicon bottom cells yielding a high accumulated short-circuit current density of 40.2 mA/cm2 and reaching a stabilized power conversion efficiency of >30%. This work paves the way toward industry-compatible, highly efficient tandem cells based on a production-compatible SHJ bottom cell.

Resistivity analysis on the enhancement of silicon heterojunction solar cells in light-thermal treatment

Enhancement of silicon heterojunction (SHJ) solar cells by light-thermal treatment has been analyzed in terms of their electrical resistivity changes. Three types of transmission line model (TLM) structures were prepared to analyze the changes of the solar cells in their Ag/ITO contact resistivity, and electron and hole transport resistivity respectively, in the light-thermal processes. The results showed that the contact resistivity of Ag/ITO increased by 88.5 mΩ cm2 and the transport performance improvement of holes is significantly better than that of electrons. Further examinations showed that the former was due to the deterioration of the ITO films, while the latter was due to the enhanced dark conductivity of doped a-Si:H layers and the different performance between (n)a-Si:H and (p)a-Si:H during the light-thermal process. A general efficiency gain of 0.3%abs was found for this batch of solar cells. An alternative batch of SHJ solar cells with better ITO films grown elsewhere, which did not deteriorate in the light-thermal process, was found to achieve 0.5%abs gain in efficiency by the same light-thermal process.

Failure modes of silicon heterojunction photovoltaic modules in damp heat environment: Sodium and moisture effects

Silicon heterojunction (SHJ) solar cells are expected to gain significant market share in the coming years. In the field, among identified degradation modes, moisture-induced degradation can be a significant concern for this solar cell technology and should be monitored. This work investigates the moisture-induced degradation mechanisms in SHJ cells encapsulated in different module configurations. Damp heat (DH) testing was performed under IEC 61215 standard conditions (85 °C and 85% relative humidity) for up to 2000 h. Different degradation mechanisms are identified after DH aging, due to moisture alone or in combination with sodium ions originating from photovoltaic glass leaching. Under the influence of moisture, these ions can migrate into the cell and degrade the cell passivation, resulting in massive power losses up to 57.6% of the initial value after 1500 h of DH aging. By using other types of glass, glass-glass module configurations show less than 3% of power losses after 2000 h of DH aging. The front side of the cell is much more sensitive than the rear side where the emitter of the cell is. After highlighting the impact of sodium, moisture alone was studied with a module configuration without glass. In that case, the degradation is characterized by increased series resistance without passivation losses.

Improved electrical contact properties in Indium-free silicon heterojunction solar cells with amorphous SnO2 TCO layers

Silicon heterojunction (SHJ) solar cells are recognized as one of the most efficient architectures in silicon-based photovoltaic devices. However, the reliance on indium (In)-based transparent conductive oxides (TCO) is anticipated to constrain their production capacity due to the critical and economically volatile nature of In. Recently, low-temperature-grown amorphous SnO2 (a-SnO2) films have been explored as an earth-abundant alternative TCO material. In this study, we examine the electrical contact properties of a-SnO2 layers employed as TCO layers in SHJ cells, focusing on their interaction with the underlying carrier selective contact layers. Our findings indicate that a stack of doped amorphous silicon (a-Si:H) and a-SnO2 exhibits relatively high specific contact resistivity, leading to a significant reduction in the device's fill factor. To address this issue, we propose two approaches: the insertion of a thin ZnO-based TCO layer between a-Si:H and a-SnO2, and the use of nanocrystalline silicon layers in place of a-Si:H. Both approaches effectively reduce the contact resistivity, resulting in improvements in fill factor and conversion efficiency comparable to those of benchmark device with In-based TCOs. Based on these findings, we demonstrate a high-efficiency, In-free, SnO2-based SHJ cell.

A novel dual functional gradient Zn(O,S)/Mg electron-selective contact for dopant‐free silicon solar cells with efficiencies approaching 21 %

Dopant-free carrier-selective contacts have the potential to mitigate or eliminate parasitic absorption, auger recombination losses, etc. Therefore, the vigorous development of dopant-free carrier-selective contact materials is an important way to enhance the performance of crystalline silicon (c-Si) photovoltaics. This study presents the concept of magnetron sputtering gradient deposited zinc oxide (Gd-Zn(O,S)) combined with a low work function magnesium metal layer. Subsequently, the Gd-Zn(O,S)/Mg bifunctional layer was further investigated and optimised to determine its suitability as a contact layer for electron transfer in c-Si solar cells. This strategy simultaneously enables a good passivation and a low contact resistance. The c-Si(n)/a-Si:H(i)/Gd-Zn(O,S)/Mg devices are constructed and achieved an optimal contact recombination current density (J0) of approximately 1.51 fA cm−2, along with a minimum ρc of approximately 35.89 mΩ.cm2. As a consequence, the power conversion efficiency of a prototype silicon heterojunction solar cell is 20.92 %. This study demonstrates that the strategy of replacing the a-Si:H(n) electron transport layer with Gd-Zn(O,S) is an effective approach for improving the SHJ cell. This study also provides new perspectives for designing novel dopant-free carrier-selective contact structures.

Signal Components and Impedance Spectroscopy of Potential p‐Si/n‐CdS/ALD‐ZnO Solar Cells: EIS and SCAPS‐1D Treatments

AbstractA silicon heterojunction (SHJ) solar cell with the attractive and widely used atomic layer deposited (ALD)‐ZnO/n‐CdS/p‐Si configuration is examined in this work to learn more about its electrical properties. Using EIS and SCAPS‐1D, a comprehensive model of the device is created and then simulated. Theoretical aspects of the cell are examined through the use of similar electrical circuit models, focusing on the transmittance spectrum made possible by the ALD‐ZnO layer's low reflectance and high visible transmittance. In this study, the C–V tool is used to study the trap states in the silicon absorber layer under different lighting conditions and wavelengths. The doping concentration and built‐in potential are determined using the Mott–Schottky technique. In addition, the cell's properties are investigated by measuring its G–V, G–F, C–T, and C–F in different real‐world scenarios. As a means of visualizing the electrochemical impedance data, Nyquist plots—sometimes called Cole–Cole plots—are utilized. By utilizing absolute impedance and phase shifts, Bode plots are employed to examine the system's frequency response. Last, the results of the SHJ cell's spectral response measurements are given, which confirm the results of the Nyquist plots.

Tantalum doped tin oxide enabled indium-free silicon heterojunction solar cells with efficiency over 25 %

Reducing indium consumption has received increasing attention in contact schemes of high efficiency silicon heterojunction (SHJ) solar cells. It is imperative to discover suitable, low-cost, and resource-abundant transparent electrodes to replace the conventional, resource-scarce indium-based transparent electrodes. Herein, tantalum doped tin oxide (TTO), prepared through low-temperature sputtering, is selected as an alternative material. Notably, the Anti-Burstein-Moss effect of TTO is observed, which is ascribed to variations of stress in films. Based on this finding, TTO was first applied to SHJ solar cells, and the photoelectric tradeoff in front and rear contacts is gained by matching nanocrystalline silicon layers and adjusting TTO thickness. Ultimately, an indium-free SHJ solar cell with an efficiency of 25.15 % is obtained (certified efficiency 25.10 %, 274.30 cm2).

Enhancing Conductivity in Silicon Heterojunction Solar Cells with Silver Nanowire-Assisted Ti3C2Tx MXene Electrodes for Cost-Effective and Scalable Photovoltaics.

Silicon heterojunction (SHJ) solar cells have set world-record efficiencies among single-junction silicon solar cells, accelerating their commercial deployment. Despite these clear efficiency advantages, the high costs associated with low-temperature silver pastes (LTSP) for metallization have driven the search for more economical alternatives in mass production. 2D transition metal carbides (MXenes) have attracted significant attention due to their tunable optoelectronic properties and metal-like conductivity, the highest among all solution-processed 2D materials. MXenes have emerged as a cost-effective alternative for rear-side electrodes in SHJ solar cells. However, the use of MXene electrodes has so far been limited to lab-scale SHJ solar cells. The efficiency of these devices has been constrained by a fill factor (FF) of under 73%, primarily due to suboptimal charge transport at the contact layer/MXene interface. Herein, a silver nanowire (AgNW)-assisted Ti3C2Tx MXene electrode contact is introduced and explores the potential of this hybrid electrode in industry-scale solar cells. By incorporating this hybrid electrode into SHJ solar cells, 9.0 cm2 cells are achieved with an efficiency of 24.04% (FF of 81.64%) and 252 cm2 cells with an efficiency of 22.17% (FFof 76.86%), among the top-performing SHJ devices with non-metallic electrodes to date. Additionally, the stability and cost-effectiveness of these solar cells are discussed.

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.

Low-cost deposition of tunable band gap Zn(O,S) as electron transport layer for crystalline silicon heterojunction solar cells

In recent years, the research on silicon heterojunction (HJT) solar cells based on dopant-free contacts has experienced rapid development. Zn(O,S) is a low work function n-type semiconductor compound with tunable band gap that can be used as the electron transport layer (ETL) in HJT solar cells. In our work, we choose Zn(O,S) as ETL and deposit it via the low-cost chemical bath deposition (CBD) method. Uniform and fast growth of Zn(O,S) films can be obtained by regulating the concentration of the complexing agent and the ratio of reactants to reduce the generation of impurities. To further achieve band matching with c-Si, the Zn(O,S) films are processed with air-annealing to modify the elemental ratios. The air-annealing lowers the interfacial electron transport barrier, which promotes charge separation and transport, thus reducing carrier recombination at the interface. Finally, the PCE of HJT solar cell based on CBD-Zn(O,S) ETL is close to 15 %, providing a new potential route for the development of low-cost HJT solar cells.

A Review: Application of Doped Hydrogenated Nanocrystalline Silicon Oxide in High Efficiency Solar Cell Devices.

Due to the unique microstructure of hydrogenated nanocrystalline silicon oxide (nc-SiOx:H), the optoelectronic properties of this material can be tuned over a wide range, which makes it adaptable to different solar cell applications. In this work, the authors review the material properties of nc-SiOx:H and the versatility of its applications in different types of solar cells. The review starts by introducing the growth principle of doped nc-SiOx:H layers, the effect of oxygen content on the material properties, and the relationship between optoelectronic properties and its microstructure. A theoretical analysis of charge carrier transport mechanisms in silicon heterojunction (SHJ) solar cells with wide band gap layers is then presented. Afterwards, the authors focus on the recent developments in the implementation of nc-SiOx:H and hydrogenated amorphous silicon oxide (a-SiOx:H) films for SHJ, passivating contacts, and perovskite/silicon tandem devices.