Passivating Contacts Research Articles

Study on selective emitter fabrication through an innovative pre‐diffusion process for enhanced efficiency in TOPCon solar cells

AbstractTOPCon (tunnel oxide passivated contact) solar cell is the mainstream high‐efficiency crystalline silicon solar cell structure. However, the lack of efficient passivation contact mechanisms on the front surface restricts the electrical performance ability to improve further. Selective emitter (SE) technology, considered a potential solution, needs to be more mature. This work provides a unique thermal pre‐diffusion approach combined with laser treatment and post‐oxidation annealing to create SE structures in TOPCon solar cells. Times for the high‐temperature process are equivalent to those for a traditional homogenous emitter. The innovative thermal pre‐diffusion process created a unique boron doping profile, achieving a high surface concentration of nearly 1 × 1020 cm−3 with a shallow junction depth of approximately 0.25 μm. Laser treatment further activated boron and facilitated its diffusion, influenced by the boron silicate glass layer and surface boron atoms. Adjustments were made to improve the pre‐diffusion recipe, including an additional boron deposition step, increasing non‐activated boron atoms. Introducing larger pyramidal microstructures also improved the junction depth and surface concentration in the heavily doped region. Compared to homogeneous emitters, the SE structures exhibited lower surface concentration in the lightly doped region, reducing the recombination current density in the passivation region J0,pass values. The SE structures achieved higher junction depths, limiting metal atom diffusion and reducing the current recombination density in the metal contact region J0,metal values. The contact resistivity between metal and silicon was also decreased. Overall, introducing SE structures resulted in a batch‐average efficiency improvement of 0.26%, reaching an average efficiency of 25.22% for TOPCon solar cells, and has industrial mass‐producible.

Electron contact interlayers for low‐temperature‐processed crystalline silicon solar cells

AbstractThis study focuses on electron‐selective passivating contacts for crystalline silicon (c‐Si) solar cells where an interlayer is used to provide a low contact resistivity between the c‐Si substrate and the metal electrode. These electron contact interlayers are used in combination with other passivating interlayers (e.g., a‐Si:H, TiOx, and Nb2O5) to improve surface passivation whilst still permitting contact resistivities suitable for high‐efficiency solar cells. We show that a wide variety of thermally evaporated materials, most of which have ionic character, enable an Ohmic contact between n‐type c‐Si and Al. From this pool of compounds, we observed that CsBr has especially promising behavior because of its excellent performance and thermal stability when combined with thin passivating layers. With different test structures, we were able to demonstrate low contact resistance using TiOx/CsBr, Nb2O5/CsBr, and a‐Si:H/CsBr stacks on n‐type c‐Si. The quality of the provided surface passivation depended on the stack but we achieved the best overall passivation stability with TiOx/CsBr. Finally, we were able to demonstrate an efficiency >20% on a laboratory‐scale solar cell that implements the TiOx/CsBr/Al stack as full‐area rear‐side electron selective contact.

Freezing Halide Segregation Under Intense Light for Photostable Perovskite/Silicon Tandem Solar Cells

AbstractPhoto‐induced halide segregation in wide‐bandgap (WBG) perovskite leads to poor stability and limits its application in high‐efficiency tandem solar cells. Here, a simple solution strategy to achieve photostable WBG perovskite solar cells (PSCs) with bandgap of ≈1.67 eV by ionic coupling potassium sorbate with defects at the buried perovskite interface is reported. Moreover, the ionic coupled potassium sorbate (ICPS) enables to control the formation of N‐methyl formamidinium ions that can selectively passivate the perovskite defects at grain boundaries. As a result, the photo‐induced halide segregation in the target perovskite films is frozen under intense light. The target single‐junction WBG PSC achieves a record efficiency of 22.00% with an open‐circuit voltage (VOC) of 1.272 V and photostability of less than 2% decay over 2000 h of operation. Perovskite/Silicon tandem solar cells are also fabricated that achieve an efficiency of 30.72% (certified 30.09% @1.087 cm2), which is the highest efficiency reported to date with a tunneling oxide passivating contact (TOPCon) c‐Si substrate. The encapsulated tandem device can maintain 97% of its initial efficiency after 1000 h of operation.

Noncontact Layer Stabilization of Azafullerene Radicals: Route toward High-Spin-Density Surfaces.

We deposit azafullerene C59N• radicals in a vacuum on the Au(111) surface for layer thicknesses between 0.35 and 2.1 monolayers (ML). The layers are characterized using X-ray photoemission (XPS) and X-ray absorption fine structure (NEXAFS) spectroscopy, low-temperature scanning tunneling microscopy (STM), and by density functional calculations (DFT). The singly unoccupied C59N orbital (SUMO) has been identified in the N 1s NEXAFS/XPS spectra of C59N layers as a spectroscopic fingerprint of the molecular radical state. At low molecular coverages (up to 1 ML), films of monomeric C59N are stabilized with the nonbonded carbon orbital neighboring the nitrogen oriented toward the Au substrate, whereas in-plane intermolecular coupling into diamagnetic (C59N)2 dimers takes over toward the completion of the second layer. By following the C59N• SUMO peak intensity with increasing molecular coverage, we identify an intermediate high-spin-density phase between 1 and 2 ML, where uncoupled C59N• monomers in the second layer with pronounced radical character are formed. We argue that the C59N• radical stabilization of this supramonolayer phase of monomers is achieved by suppressed coupling to the substrate. This results from molecular isolation on top of the passivating azafullerene contact layer, which can be explored for molecular radical state stabilization and positioning on solid substrates.

Novel Interlayer Boosting the Performance of Evaporated Cu2O Hole‐Selective Contacts in Si Solar Cells

Passivating contacts based on transition metal oxides are of great interest for applications in crystalline silicon (c‐Si) solar cells due to their improved optical transparency and potential cost reduction. In this work, the contact resistivity and passivation for thermally evaporated Cu2O are investigated and optimized, with and without an Al2O3 interlayer, as a hole‐selective contact to c‐Si. Additionally, we implement an Al y TiO x /TiO2 stack as a novel passivating tunnel interlayer for hole‐selective contacts, achieving an implied open‐circuit voltage iV oc of 630 mV and a record‐low J 0 of 212 fA cm−2 while maintaining a contact resistivity ρ c of 62 mΩ cm2. A record‐low ρ c of 8 mΩ cm2 for Cu2O‐based contacts is also demonstrated at the expense of passivation. The addition of the interlayer resulted in a 2% absolute improvement in the efficiency of proof‐of‐concept c‐Si cells with full‐area rear Cu2O contacts, reaching 19.1%.The demonstration of this novel interlayer stack provides new avenues to improve the performance also of other hole‐selective passivating contacts.

Improved Localized Laser Doping of Boron‐Doped Si Paste for High‐Efficiency Solar Cells

Laser doping (LD) of born‐doped Si paste (Si paste) is a potential boron‐doping approach for advanced solar cells. It is aimed to develop a top‐hat LD instead of a Gaussian LD and a rear‐side polishing process to fabricate P++ local contacts for improved passivated emitter and rear contact (i‐PERC) cells. With the help of vision alignment, LD is conducted on a dashed line pattern of printed Si paste, which decreases the consumption of paste. The variations of boron content in Si paste and the laser pulse energy density can help customize the doping profile. The predicted result of the boron LD profile is a peak dopant density of 2 × 1019 atoms cm−3 and a dopant depth of over 4.0 μm. When higher firing temperature, it can obtain thicker localized back surface field of over 7 μm, since the gradient of the residual Si concentration at the Al/Si interface can suppress the formation of voids. The overall increment in fill factor, short‐circuit current, and open‐circuit voltage enhances the average efficiency by 0.11% for i‐PERC cells and 0.09% for i‐bifacial PERC cells, respectively, due to the improved local contacts.

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.

Investigation of sub-stoichiometric MoOx hole-selective contacts for rear junction passivating contact silicon solar cells

Carrier-selective contacts play a crucial role in improving the performance of silicon solar cells by reducing recombination losses. This study explores the use of sub-stoichiometric molybdenum oxide (MoOx) as a hole-selective contact material deposited via thermal evaporation. X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) analysis reveal diverse Mo–O bonding configurations and a low work function of ∼5.02 eV for the MoOx film. The passivation properties of a cell-like structure with local MoOx contact are found to be comparable to those of a structure with a full front passivation layer, as evidenced by an implied open-circuit voltage (iVoc) of 703.2 mV. However, the conversion efficiency of the solar cell with MoOx contact is limited to 16.5 %, with reduced external quantum efficiency (EQE) at UV and visible wavelengths. The study proposes that optimizing the MoOx front contact's work function and passivation characteristics could improve the solar cell's efficiency to 21.8 %. This research demonstrates the potential of sub-stoichiometric MoOx as a promising hole-selective contact for silicon solar cells, highlighting the factors influencing its performance.

Highly reflective and passivated ohmic contacts in p-Ge by laser processing of aSiCx:H(i)/Al2O3/aSiC films for thermophotovoltaic applications

Crystalline germanium (c-Ge) has historically been regarded as a cost-effective alternative to III-V semiconductors for thermophotovoltaic (TPV) device fabrication. However, Ge-based devices have not yet reported high efficiencies, partially due to the lack of an efficient back-surface reflector that turns back to the heat source out-band (sub-bandgap) thermal radiation. The difficulty of implementing back surface reflectors in Ge TPV cells is related to the simultaneous requirement of good back surface passivation, low electrical resistivity, and high out-band optical reflectivity. In this study, we demonstrate a highly reflective ohmic contact to p-type c-Ge (doping concentration of 2 × 1015 cm−3) made of an aSiCx(1 nm)/Al2O3 (50 nm)/aSiC (45 nm) stack that is laser processed using Nd:YVO4 laser emitting at 355 nm to create punctual p+ contacts (locally diffused Al regions). This stack is finally caped with a thick (1000 nm) Al layer that behaves as a metallic mirror and back electrode. As the laser processed area increases from 0.1 to 3 %, which is the typical range in the final devices, the surface recombination velocity increase from 10.5 to 60.0 cm/s, while the effective contact resistance reduces from 0.462 to 0.036 Ω cm2. Moreover, a sub-bandgap reflectance of 90–98 % is achieved. Simulations assuming ideal device configuration indicate that implementing these back contacts could potentially enable TPV cell conversion efficiencies comparable to the reported high-efficiency c-Ge TPV cells operating at similar illumination temperature.

Enhancing the open-circuit voltage in narrow-bandgap CuInSe2 solar cells via local contact passivation with Al2O3

A fabrication technique using Al2O3-passivated local contacts was employed to produce narrow-bandgap CuInSe2 (CISe) photoabsorbers, which are well-suited as bottom cell materials in tandem devices. However, the performances of CISe cells with narrow bandgaps are impeded by the recombination of charge carriers, which reduces the open-circuit voltage (VOC). To overcome this limitation, an additional Al2O3 passivation layer was added to CISe solar cells. This enhanced the VOC while maintaining a spectral response of up to 1.0 eV, thereby boosting the photovoltaic conversion efficiency of the devices. Further, the Al2O3 passivation layer within the CISe absorber effectively mitigated the recombination of charge carriers, resulting in a substantial improvement in efficiency. Specifically, the Al2O3-passivated local contact hindered the charge-carrier recombination at the rear contact, leading to a marked increase in the VOC. Consequently, the overall photovoltaic conversion efficiency increased significantly from 10.4 % to 13 %. These results are expected to greatly further the development of CISe solar cells and achieve remarkable photovoltaic conversion efficiencies.

Conductive passivating contact for high fill factor monolithic perovskite/silicon tandem solar cells

AbstractPerovskite/silicon tandem solar cells (PK/Si TSCs) blaze the way in pushing power conversion efficiency (PCE) beyond the single‐junction Shockley–Queisser limit. Meanwhile, localized defects in perovskite subcells result in a lower fill factor (FF), which limits further improvement of PCE in PK/Si TSCs. Herein, we report a conductive passivation contact layer by posttreatment of bis(2‐hydroxyethyl)dimethylammonium chloride (BDAC) zwitterion molecule on the perovskite surface. It can passivate the positive and negative localized defects, inhibit the formation of Pb0, and spontaneously convert the perovskite surface to be a more n‐type conductive contact layer for charge separation. These combined enhancements enabled a PCE of 21.4% with an enhanced VOC of 80 mV and an FF of 82.84% for the inverted single‐junction device prepared by the two‐step method. Moreover, BDAC passivation achieved a PCE of 28.67% with an FF of 80.02% for PK/Si TSCs. In addition, the scaling‐up device with an active area of 11.879 cm2 delivers a PCE of 24.46%, and a minimodule with power conversion over 2 W is designed and fabricated.

Soft deposition of TCOs by pulsed laser for high-quality ultra-thin poly-Si passivating contacts

In this work, the applicability of pulsed laser deposition (PLD) of transparent conductive oxides (TCOs) on high-quality ultra-thin poly-Si based passivating contacts is explored. Parasitic absorption caused by poly-Si layers can be minimized by reducing the poly-Si layer thickness. However, TCO deposition on poly-Si contacts, commonly by sputtering, results in severe deposition-induced damage and further aggravates the surface passivation for thinner poly-Si layers (<20 nm). Although a thermal treatment at elevated temperature (∼350 °C) can be used to partially repair the surface passivation quality, the contact resistivity severely increases due to the formation of a parasitic oxide layer at the poly-Si/ITO interface. Alternatively, we show that PLD TCOs can be used to mitigate the damage on ultra-thin (∼10 nm) poly-Si layers. Further improvement in poly-Si contact passivation can be achieved by increasing the deposition pressure while low contact resistivities (∼45 mΩ cm2) and good thermal stability (up to 350 °C) are achieved with a PLD indium-doped tin oxide (ITO) layer on high-quality ultra-thin poly-Si(n+) contacts. This allows for the application of a highly transparent front side contact by combining the excellent opto-electrical properties of a PLD ITO film with a 10 nm thin poly-Si contact.

Understanding and mitigating resistive losses in fired passivating contacts: role of the interfaces and optimization of the thermal budget

This work presents a study of p-type passivating contacts based on SiCx formed via a rapid thermal processing (RTP) step, using conditions compatible with the firing used to sinter screen-printed metallization pastes in industry. The contributions of the two interfaces (wafer/contact and contact/metal) to the contact resistivity are first decorrelated, identifying tunnelling at the wafer interface as the main contribution. We then investigate the influence of the active dopant concentration on the contact resistivity and the SiCx sheet resistance and propose strategies to reduce both resistances by increasing the thermal budget applied during RTP. Lastly, we discuss potentials and limitations of implementing the investigated stacks as rear side contacts of p-type devices with localized metallization. We demonstrate that increasing the thermal budget during RTP can effectively mitigate resistive losses and enhance contact performance and we show that an oxide layer that can withstand high thermal budgets is the key factor for obtaining simultaneously high passivation quality and good electrical properties. We investigate three different oxide types grown by HNO3 immersion, UV-O3 exposure and N2O plasma oxidation. The latter is demonstrated to be a promising candidate for an application in devices fabricated with high RTP thermal budget.

Optimization of efficiency enhancement of TOPCon cells with boron selective emitter

Silicon solar cells with a tunnel oxide passivating contact (TOPCon) structure are the new mainstream products; however, emitter recombination has become the bottleneck for further improvement. The introduction of selective emitter (SE) technology becomes imperative to address this issue. In this study, the appropriate range of sheet resistance in the light-doped region (230–280 Ω/sq)and the reasonable interval of the diffusion junction depth in the heavy-doped region (1.2–1.3 μm) are presented. The selective emitter with a suitable doping distribution is realized using the mask and etch-back method. Compared to the homogeneous emitter with a sheet resistance of 150 Ω/sq, J0e of 16 fA/cm2, and J0metal-front of 500 fA/cm2, the optimum selective emitter results in a J0e-light doping of 8 fA/cm2, J0e-heavy doping of 45 fA/cm2 and J0metal-front of 213 fA/cm2. Finally, the boron SE-TOPCon cell samples UOC (726.5 mV), FF (84.01%), and efficiency (25.51%) are obtained, compared with the TOPCon cell with homogeneous emitter Uoc (717.6 mV), FF (83.77%) and efficiency (25.17%) of the reference. In addition, the efficiency potential of the boron SE-TOPCon cell (26.02%) at the optimal process conditions is determined based on device simulations. This study provides a feasible technical path for mass-produced TOPCon cells to increase the efficiency to more than 26%.

Design Rule of Electron- and Hole-Selective Contacts for Polycrystalline Silicon-Based Passivating Contact Solar Cells.

A crystalline silicon (c-Si) solar cell with a polycrystalline silicon/SiOx (poly-Si/SiOx) structure, incorporating both electron and hole contacts, is an attractive choice for achieving ideal carrier selectivity and serving as a fundamental component in high-efficiency perovskite/Si tandem and interdigitated back-contact solar cells. However, our understanding of the carrier transport mechanism of hole contacts remains limited owing to insufficient studies dedicated to its investigation. There is also a lack of comparative studies on the poly-Si/SiOx electron and hole contacts for ideal carrier-selective solar cells. Therefore, this study aims to address these knowledge gaps by exploring the relationship among microstructural evolution, dopant in-diffusion, and the resulting carrier transport mechanism in both the electron and hole contacts of poly-Si/SiOx solar cells. Electron (n+ poly-Si/SiOx/substrate)- and hole (p+ poly-Si/SiOx/substrate)-selective passivating contacts are subjected to thermal annealing. Changes in the passivation properties and carrier transport mechanisms of these contacts are investigated during thermal annealing at various temperatures. Notably, the results demonstrate that the passivation properties and carrier transport mechanisms are strongly influenced by the microstructural evolution of the poly-Si/SiOx layer stack and dopant in-diffusion. Furthermore, electron and hole contacts exhibit common behaviors regarding microstructural evolution and dopant in-diffusion. However, the hole contacts exhibit relatively inferior electrical properties overall, mainly because both the SiOx interface and the p+ poly-Si are found to be highly defective. Moreover, boron in the hole contacts diffuses deeper than phosphorus in the electron contacts, resulting in deteriorated carrier collection. The experimental results are also supported by device simulation. Based on these findings, design rules are suggested for both electron and hole contacts, such as using thicker SiOx and/or annealing the solar cell at a temperature not exceeding the critical annealing temperature of the hole contacts.

Theoretical analysis of backside polycrystalline silicon layer in the TOPCon solar cells

As an upgraded version of passivated emitter and rear cell (PERC) solar cells, the performance of tunnel oxide passivating contacts (TOPCon) solar cells is very dependent on the silicon oxide layer and poly-Si layer. We found that different crystallization rates or doping of germanium, carbon and other elements in poly-Si can change the band gap of poly-Si, which has an impact on the efficiency (Eff) of TOPCon solar cells. Therefore, the appropriate band gap is particularly important. At the same time, the internal defect of poly-Si also have great influence on the performance of solar cells. The simulated band diagram, charge carrier concentration and recombination rate were used to deeply explore the defect in poly-Si and the influence of poly-Si with different band gap on the performance of TOPCon solar cells.

Dramatic Reduction of Silicon Surface Recombination by ALD TiOx Capping Layer from TiCl4 and H2O: The Role of Chlorine.

Amorphous thin-film TiOx prepared via atomic layer deposition (ALD) has been identified as one of the most promising materials for use in transparent passivating contacts in high-efficiency and low-cost crystalline silicon (c-Si) solar cells. As highlighted in this work, the passivation performance of ALD TiOx layers strongly depends on the metal precursor used, with films prepared using TiCl4 recently showing the best results. However, a full understanding of how such films achieve their high level of surface passivation has not yet been demonstrated. This study provides a clear demonstration that a key part of this passivation mechanism is due to chlorine (Cl) accumulation at the Si surface. This mechanism is demonstrated to be quite general in nature by showing how 2 nm of ALD TiOx (TiCl4 + H2O) can be applied as a capping layer for either ZnO or Al2O3 interlayers to dramatically reduce silicon surface recombination. Cl depth profiles obtained using secondary ion mass spectrometry confirm the presence of Cl extending through the depth of the interlayers with a peak at the silicon interface. Remarkably, this diffusion of Cl is observed following low-temperature (75 °C) deposition of the TiOx capping layer, without any subsequent thermal treatment. Contrary to earlier studies that treated residual Cl in ALD films as a general contamination issue, these findings reveal unequivocally that chlorine plays a crucial role in Si surface passivation and can be classed as an effective passivation element, similar to hydrogen in its ability to passivate Si dangling bonds. The outcomes of this research emphasize the importance of residual chlorine in enhancing the passivation of buried interfaces and provide additional motivation for employing metal chloride precursors for silicon surface passivation applications.

Fabrication and characterization of SiC-based transparent passivating contacts for enhanced photovoltaic performance

Silicon Carbide (SiC) passivating contacts are thought to be an emerging solution to bridge the existing gap in the silicon-based solar market. Passivating contacts directly tackle the intrinsic metal-semiconductor interfaces issues like recombination losses and Fermi-level pinning. Considering this approach, SiC-based Transparent Passivating Contacts (TPC) are fabricated on n-Si <100> using RF magnetron sputtering at multiple RF powers for enhanced solar cell performance. All said contacts were convolved through a variety of optical, and electrical techniques. It is confirmed that the passivating contacts grown by higher RF power have an enhanced provision for both transmission and contact passivation. Additionally, it has been found that a sufficient amount of oxygen vacancies (VO) are located at the SiC/Si interface and are mainly responsible for limiting of the contact passivation. This issue might be resolved by opting for larger RF power during the SiC growth that may suppress VO impact. Further, purely optical and electro-optical parameters and their dependence on VO have been readily studied. Most importantly the extent of contact passivation has been readily measured by the transient of photo voltages and Q-DLTS techniques and cross-verified by current kinetics studies. It is found by the current-voltage and energy band picture that the SiC grown at higher RF would provide better contact passivation with surface resistance of ∼109 Ω and positive trap centers, respectively.

Detailed investigation of electrical and optical properties of textured n-type and roughened p-type tunnel oxide passivated contacts for screen-printed double-side passivated contact silicon solar cell application

This paper presents detailed characterization and analyses of the optical, electrical, and contact properties of a 35 nm phosphorus-doped (n-type) polysilicon (poly-Si) and a 250 nm boron-doped (p-type) poly-Si deposited respectively on textured and roughed surface. These layers could be applied respectively to the front and rear sides of an n-type Si to produce back junction bifacial screen-printed double-side tunnel oxide passivated contacts (DS-TOPCon) solar cells. Optical and device modeling revealed a short circuit current density loss of 1.5 mA/cm2 and 0.5 mA/cm2 due to absorption in the front n-TOPCon and rear side p-TOPCon layers, respectively. The passivation and contact properties including metalized and unmetallized recombination current density (J0), as well as contact resistivity, were determined as a function of contact firing temperature in the range of 700∼800℃. The passivation quality of the front thin n-TOPCon was found to deteriorate with increased firing temperature while the rear thick p-TOPCon improved. The study showed that the simulated contact firing at 730℃ resulted in the best unmetallized double-side TOPCon precursor, with an excellent implied open-circuit voltage of 730 mV and implied fill factor of ∼86 %. However, the metalized J0 increased and contact resistivity decreased monotonically with the increase in the firing temperature. The 2D device simulations revealed that these layers can produce screen-printed DS-TOPCon cells with an efficiency of ∼22.5 %. Solar cell modeling also showed that the DS-TOPCon solar cell efficiency can reach 24.1 % by decreasing the n-TOPCon thickness to 20 nm and lowering the full area metalized J0 to ∼100 mA/cm2.

Rational Approach for High‐Efficiency Dopant‐Free Solar Cells Characterized with Key Parameters

Crystalline silicon (c‐Si) solar cells have dominated the photovoltaic market due to their superior mechanical and thermal robustness, nonhazardous nature, optimal energy bandgap, and the availability of established manufacturing techniques. However, conventional c‐Si solar cells fabricated through thermal doping processes present challenges such as high recombination rates and increased production costs. Recently, dopant‐free solar cells have emerged as a promising next‐generation approach; they offer numerous advantages, such as reduced recombination, cost‐effectiveness, environmental friendliness, and applicability to nano‐ and submicrometer structures. This review evaluates the strengths and weaknesses of dopant‐free passivating contact materials for emitters, tracing the development of dopant‐free solar cells from the earliest reports to the current state‐of‐the‐art. A systematic evaluation of these materials based on their electrical and optical properties, coating conformality, stability, and overall photovoltaic performance is presented. Moreover, the limitations of dopant‐free solar cells are identified and strategies to further enhance their efficiency are proposed.