Efficient silicon heterojunction solar cells based on p‐ and n‐type substrates processed at temperatures < 220°C

We present the optimization and characterization of heterojunction solar cells consisting of an amorphous silicon emitter, a single crystalline absorber and an amorphous silicon rear side which causes the formation of a back surface field (a‐Si:H/c‐Si/a‐Si:H). The solar cells were processed at temperatures <220°C. An optimum of the gas phase doping concentration of the a‐Si:H layers was found. For high gas phase doping concentrations, recombination via defects located at or nearby the interface leads to a decrease in solar cell efficiency. We achieved efficiencies >17% on p‐type c‐Si absorbers and >17·5% on n‐type absorbers. In contrast to the approach of Sanyo, no additional intrinsic a‐Si:H layers between the substrate and the doped a‐Si:H layers were inserted. Copyright © 2006 John Wiley & Sons, Ltd.     

CuOx/a‐Si:H heterojunction thin‐film solar cell with an n‐type µc‐Si:H depletion‐assisting layer

We showed that thin n‐type CuO_x films can be deposited by radio‐frequency magnetron reactive sputtering and demonstrated the fabrication of n‐CuO_x/intrinsic hydrogenated amorphous silicon (i‐a‐Si:H) heterojunction solar cells (HSCs) for the first time. A highly n‐doped hydrogenated microcrystalline Si (n‐µc‐Si:H) layer was introduced as a depletion‐assisting layer to further improve the performance of n‐CuO_x/i‐a‐Si:H HSCs. An analysis of the external quantum efficiency and energy‐band diagram showed that the thin depletion‐assisting layer helped establish sufficient depletion and increased the built‐in potential in the n‐CuO_x layer. The fabricated HSC exhibited a high open‐circuit voltage of 0.715 V and an efficiency of 4.79%. Copyright © 2015 John Wiley & Sons, Ltd.     

Laser‐fired contact optimization in c‐Si solar cells

In this work we study the optimization of laser‐fired contact (LFC) processing parameters, namely laser power and number of pulses, based on the electrical resistance measurement of an aluminum single LFC point. LFC process has been made through four passivation layers that are typically used in c‐Si and mc‐Si solar cell fabrication: thermally grown silicon oxide (SiO₂), deposited phosphorus‐doped amorphous silicon carbide (a‐SiC_x/H(n)), aluminum oxide (Al₂O₃) and silicon nitride (SiN_x/H) films. Values for the LFC resistance normalized by the laser spot area in the range of 0.65–3 mΩ cm² have been obtained. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface passivation of high‐efficiency silicon solar cells by atomic‐layer‐deposited Al2O3

Atomic‐layer‐deposited aluminium oxide (Al₂O₃) is applied as rear‐surface‐passivating dielectric layer to passivated emitter and rear cell (PERC)‐type crystalline silicon (c‐Si) solar cells. The excellent passivation of low‐resistivity p‐type silicon by the negative‐charge‐dielectric Al₂O₃ is confirmed on the device level by an independently confirmed energy conversion efficiency of 20·6%. The best results are obtained for a stack consisting of a 30 nm Al₂O₃ film covered by a 200 nm plasma‐enhanced‐chemical‐vapour‐deposited silicon oxide (SiO_x) layer, resulting in a rear surface recombination velocity (SRV) of 70 cm/s. Comparable results are obtained for a 130 nm single‐layer of Al₂O₃, resulting in a rear SRV of 90 cm/s. Copyright © 2008 John Wiley & Sons, Ltd.     

Full‐wave optoelectrical modeling of optimized flattened light‐scattering substrate for high efficiency thin‐film silicon solar cells

The flattened light‐scattering substrate (FLiSS) is formed by a combination of two materials with a high refractive index mismatch, and it has a flat surface. A specific realization of this concept is a flattened two‐dimensional grating. When applied as a substrate for thin‐film silicon solar cells in the nip configuration, it is capable to reflect light with a high fraction of diffused component. Furthermore, the FLiSS is an ideal substrate for growing high‐quality microcrystalline silicon (µc‐Si:H), used as bottom cell absorber layer in most of multijunction solar cell architectures. FLiSS is a three‐dimensional structure; therefore, a full‐wave analysis of the electromagnetic field is necessary for its optimal implementation. Using finite element method, different shapes, materials, and geometrical parameters were investigated to obtain an optimized FLiSS. The application of the optimized FLiSS in µc‐Si:H single junction nip cell (1‐µm‐thick i‐layer) resulted in a 27.4‐mA/cm² implied photocurrent density. The absorptance of µc‐Si:H absorber exceeded the theoretical Yablonovitch limit for wavelengths larger than 750 nm. Double and triple junction nip solar cells on optimal FLiSS and with thin absorber layers were simulated. Results were in line with state‐of‐the‐art optical performance typical of solar cells with rough interfaces. After the optical optimization, a study of electrical performance was carried out by simulating current–voltage characteristics of nip solar cells on optimized FLiSS. Potential conversion efficiencies of 11.6%, 14.2%, and 16.0% for single, double, and triple junction solar cells with flat interfaces, respectively, were achieved. Copyright © 2012 John Wiley & Sons, Ltd.     

Development of a‐SiOx:H solar cells with very high Voc × FF product

In this study, deposition conditions for making a‐SiO_x:H are investigated systematically in order to obtain a high band gap material. We found that at given optical band gap, a‐SiO_x:H with favorable opto‐electronic properties can be obtained when deposited using low CO₂ flow rates and deposition pressures. We also found that a low radio frequency power density is required in order to limit the effect of ion bombardment on the material properties of i‐a‐SiO_x:H and thereby the solar cell performance. In addition, by decreasing the heater temperature from 300 to 200°C when making the i‐a‐SiO_x:H, the V_oc can be increased. We employed optimized p‐doped and n‐doped a‐SiO_x:H films into the p‐i‐n solar cells, and as a consequence, a high V_oc of over 1 V and high fill factor (FF) are obtained. When depositing on texture‐etched ZnO:Al substrates, a high efficiency a‐SiO_x:H single junction solar cell having a high V_oc × FF product of 0.761 (V_oc: 1.042 V, J_sc: 10.3 mA/cm², FF: 0.73, efficiency: 7.83%) was obtained. The a‐SiO_x:H solar cell shows comparable light degradation characteristics to standard a‐Si:H solar cells. Copyright © 2014 John Wiley & Sons, Ltd.     

High potential of thin (<1 µm) a‐Si: H/µc‐Si:H tandem solar cells

Silicon based thin tandem solar cells were fabricated by plasma enhanced chemical vapor deposition (PECVD) in a 30 × 30 cm² reactor. The layer thicknesses of the amorphous top cells and the microcrystalline bottom cells were significantly reduced compared to standard tandem cells that are optimized for high efficiency (typically with a total absorber layer thickness from 1.5 to 3 µm). The individual absorber layer thicknesses of the top and bottom cells were chosen so that the generated current densities are similar to each other. With such thin cells, having a total absorber layer thickness varying from 0.5 to 1.5 µm, initial efficiencies of 8.6–10.7% were achieved. The effects of thickness variations of both absorber layers on the device properties have been separately investigated. With the help of quantum efficiency (QE) measurements, we could demonstrate that by reducing the bottom cell thickness the top cell current density increased which is addressed to back‐reflected light. Due to a very thin a‐Si:H top cell, the thin tandem cells show a much lower degradation rate under continuous illumination at open circuit conditions compared to standard tandem and a‐Si:H single junction cells. We demonstrate that thin tandem cells of around 550 nm show better stabilized efficiencies than a‐Si:H and µc‐Si:H single junction cells of comparable thickness. The results show the high potential of thin a‐Si/µc‐Si tandem cells for cost‐effective photovoltaics. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental and simulated analysis of front versus all‐back‐contact silicon heterojunction solar cells: effect of interface and doped a‐Si:H layer defects

Front silicon heterojunction and interdigitated all‐back‐contact silicon heterojunction (IBC‐SHJ) solar cells have the potential for high efficiency and low cost because of their good surface passivation, heterojunction contacts, and low temperature fabrication processes. The performance of both heterojunction device structures depends on the interface between the crystalline silicon (c‐Si) and intrinsic amorphous silicon [(i)a‐Si:H] layer, and the defects in doped a‐Si:H emitter or base contact layers. In this paper, effective minority carrier lifetimes of c‐Si using symmetric passivation structures were measured and analyzed using an extended Shockley–Read–Hall formalism to determine the input interface parameters needed for a successful 2D simulation of fabricated baseline solar cells. Subsequently, the performance of front silicon heterojunction and IBC‐SHJ devices was simulated to determine the influence of defects at the (i)a‐Si:H/c‐Si interface and in the doped a‐Si:H layers. For the baseline device parameters, the difference between the two device configurations is caused by the emitter/base contact gap recombination and the back surface geometry of IBC‐SHJ solar cell. This work provides a guide to the optimization of both types of SHJ device performance, predicting an IBC‐SHJ solar cell efficiency of 25% for realistic material parameters. Copyright © 2013 John Wiley & Sons, Ltd.     

Wide‐bandgap p‐type microcrystalline silicon oxycarbide using additional trimethylboron for silicon heterojunction solar cells

We report a new wide‐bandgap p‐type microcrystalline silicon oxycarbide (p‐μc‐SiO_xC_y:H) film prepared by plasma‐enhanced chemical vapor deposition. As an additional doping gas, trimethylboron was introduced into the standard processing gas‐mixture of silane, carbon dioxide, hydrogen, and diborane. With both trimethylboron and diborane as doping gases, the optical bandgap (E ₀₄) of the formed p‐μc‐SiO_xC_y:H film was 0.18 eV higher than that of reference microcrystalline silicon oxide (p‐μc‐SiO_x:H) processed with only diborane doping gas for the same levels of film thickness and electrical conductivity. To demonstrate the effectiveness of the developed p‐layer, we applied it as an emitter in silicon heterojunction solar cells, which delivered a markedly high open circuit voltage of 0.702 V and a power conversion efficiency of 18.9% based on a non‐textured flat wafer. Copyright © 2017 John Wiley & Sons, Ltd.     

High‐efficiency µc‐Si solar cells made by very high‐frequency plasma‐enhanced chemical vapor deposition

Microcrystalline silicon‐based single‐junction p–i–n solar cells have been fabricated by very high‐frequency plasma enhanced chemical vapor deposition using a showerhead cathode at high pressures and under silane depletion conditions. The i‐layers are made near the transition from amorphous to crystalline. It was found that, especially at high crystalline fractions, the open‐circuit voltage and fill factor are very sensitive to the morphology of the substrate. At an i‐layer deposition rate 0·45 nm/s, we have measured a stabilised efficiency of 10% (V_oc = 0·52 V, FF = 0·74) for a cell made on texture‐etched ZnO:Al. The performance is stable under light soaking. The defect density of the absorber layer is in the 10¹⁵ cm⁻³ range. In spite of the presence of oxygen contamination, good electrical properties and good infrared cell response are obtained. Copyright © 2006 John Wiley & Sons, Ltd.     

H2 plasma treatment at the p/i interface of a hydrogenated amorphous Si absorption layer for high‐performance Si thin film solar cells

Plasma treatment (PT) of the buffer layer for highly H₂‐diluted hydrogenated amorphous silicon (a‐Si:H) absorption layers is proposed as a technique to improve efficiency and mitigate light‐induced degradation (LID) in a‐Si:H thin film solar modules. The method was verified for a‐Si:H single‐junction and a‐Si:H/microcrystalline silicon (µc‐Si:H) tandem modules with a size of 200 × 200 mm² (aperture area of 382.5 cm²) under long‐term light exposure. H₂ PT at the p/i interface was found to eliminate non‐radiative recombination centers in the buffer layer, and plasma‐enhanced chemical vapor deposition at low radio‐frequency power was found to suppress the generation of defects during the growth of a‐Si:H absorption layers on the treated buffer layers. With optimized H₂ PT of the a‐Si:H single‐junction module, the stabilized short circuit current and fill factor increased, and the stabilized open circuit voltage moves beyond its initial value. The results demonstrate 7.7% stabilized efficiency and 10.5% LID for the a‐Si:H single‐junction module and 10.82% stabilized efficiency and 7.76% LID for the a‐Si:H/µc‐Si:H tandem module. Thus, the growth of an a‐Si:H absorption layer on a H₂ PT buffer layer can be considered as a practical method for producing high‐performance Si thin film modules. Copyright © 2012 John Wiley & Sons, Ltd.     

Multi‐crystalline Si solar cells with very fast deposited (180 nm/min) passivating hot‐wire CVD silicon nitride as antireflection coating

Hot‐wire chemical vapor deposition (HWCVD) is a promising technique for very fast deposition of high quality thin films. We developed processing conditions for device‐ quality silicon nitride (a‐SiN_x:H) anti‐reflection coating (ARC) at high deposition rates of 3 nm/s. The HWCVD SiN_x layers were deposited on multicrystalline silicon (mc‐Si) solar cells provided by IMEC and ECN Solar Energy. Reference cells were provided with optimized parallel plate PECVD SiN_x and microwave PECVD SiN_x respectively. The application of HWCVD SiN_x on IMEC mc‐Si solar cells led to effective passivation, evidenced by a V_oc of 606 mV and consistent IQE curves. For further optimization, series were made with HW SiN_x (with different x) on mc‐Si solar cells from ECN Solar Energy. The best cell efficiencies were obtained for samples with a N/Si ratio of 1·2 and a high mass density of >2·9 g/cm³. The best solar cells reached an efficiency of 15·7%, which is similar to the best reference cell, made from neighboring wafers, with microwave PECVD SiN_x. The IQE measurements and high V_oc values for these cells with HW SiN_x demonstrate good bulk passivation. PC1D simulations confirm the excellent bulk‐ and surface‐passivation for HW SiN_x coatings. Interesting is the significantly higher blue response for the cells with HWCVD SiN_x when compared to the PECVD SiN_x reference cells. This difference in blue response is caused by lower light absorption of the HWCVD layers (compared to microwave CVD; ECN) and better surface passivation (compared to parallel plate PECVD; IMEC). The application of HW SiN_x as a passivating antireflection layer on mc‐Si solar cells leads to efficiencies comparable to those with optimized PECVD SiN_x coatings, although HWCVD is performed at a much higher deposition rate. Copyright © 2007 John Wiley & Sons, Ltd.     

Mitigating Plasmonic Absorption Losses at Rear Electrodes in High‐Efficiency Silicon Solar Cells Using Dopant‐Free Contact Stacks

Although charge‐carrier selectivity in conventional crystalline silicon (c‐Si) solar cells is usually realized by doping Si, the presence of dopants imposes inherent performance limitations due to parasitic absorption and carrier recombination. The development of alternative carrier‐selective contacts, using non‐Si electron and hole transport layers, has the potential to overcome such drawbacks and simultaneously reduce the cost and/or simplify the fabrication process of c‐Si solar cells. Nevertheless, devices relying on such non‐Si contacts with power conversion efficiencies (PCEs) that rival their classical counterparts are yet to be demonstrated. In this study, one key element is brought forward toward this demonstration by incorporating low‐pressure chemical vapor deposited ZnO as the electron transport layer in c‐Si solar cells. Placed at the rear of the device, it is found that rather thick (75 nm) ZnO film capped with LiF_x/Al simultaneously enables efficient electron selectivity and suppression of parasitic infrared absorption. Next, these electron‐selective contacts are integrated in c‐Si solar cells with MoO_x‐based hole‐collecting contacts at the device front to realize full‐area dopant‐free‐contact solar cells. In the proof‐of‐concept device, a PCE as high as 21.4% is demonstrated, which is a record for this novel device class and is at the level of conventional industrial solar cells.     

SiOyNx/SiNx stack: a promising surface passivation layer for high‐efficiency and potential‐induced degradation resistant mc‐silicon solar cells

A thin SiO_yN_x film was inserted below a conventional SiN_x antireflection coating used in c‐Si solar cells in order to improve the surface passivation and the solar cell's resistance to potential‐induced degradation (PID). The effect of varying the flow ratio of the N₂O and SiH₄ precursors and the deposition temperature for the SiO_yN_x thin film upon material properties were systematically investigated. An excellent surface passivation was obtained on FZ p‐type polished silicon wafers, with the best results obtained with a SiO_yN_x film deposited at a very low temperature of 130 °C and with an optical refractive index of 1.8. In the SiO_yN_x/SiN_x stack structure, a SiO_yN_x film with ~6 nm thickness is sufficient to provide excellent surface passivation with an effective surface recombination velocity S_eff < 2 cm/s. Furthermore, we applied the optimized SiO_yN_x/SiN_x stack on multicrystalline Si solar cells as a surface passivation and antireflection coating, resulting in a 0.5% absolute average conversion efficiency gain compared with that of reference cells with conventional SiN_x coating. Moreover, the cells with the SiO_yN_x/SiN_x stack layers show a significant increase in their resistance to PID. Nearly zero degradation in shunt resistance was obtained after 24 h in a PID test, while a single SiN_x‐coated silicon solar cell showed almost 50% degradation after 24 h. Copyright © 2016 John Wiley & Sons, Ltd.     

Thin film solar cells incorporating microcrystalline Si1–xGex as efficient infrared absorber: an application to double junction tandem solar cells

We have fabricated efficient (∼7–8%) hydrogenated microcrystalline Si_1–xGe_x (µc‐Si_1–xGe_x:H, x ∼ 0.1–0.17) single junction p‐i‐n solar cells with markedly higher short‐circuit current densities than for µc‐Si:H (x = 0) solar cells due to enhanced infrared absorption. By replacing the conventional µc‐Si:H with the µc‐Si_1–xGe_x:H as infrared absorber in double junction tandem solar cells, the bottom cell thickness can be reduced by more than half while preserving the current matching with hydrogenated amorphous silicon (a‐Si:H) top cell. An initial efficiency of 11.2% is obtained for a‐Si:H/µc‐Si₀.₉Ge₀.₁:H solar cell with bottom cell thickness less than 1 µm. Copyright © 2009 John Wiley & Sons, Ltd.     

Current transport studies of amorphous n/p junctions and its application in a‐Si:H/HIT‐type tandem cells

This paper presents an understanding of the fundamental carrier transport mechanism in hydrogenated amorphous silicon (a‐Si:H)‐based n/p junctions. These n/p junctions are, then, used as tunneling and recombination junctions (TRJ) in tandem solar cells, which were constructed by stacking the a‐Si:H‐based solar cell on the heterojunction with intrinsic thin layer (HIT) cell. First, the effect of activation energy (E_a) and Urbach parameter (E_u) of n‐type hydrogenated amorphous silicon (a‐Si:H(n)) on current transport in an a‐Si:H‐based n/p TRJ has been investigated. The photoluminescence spectra and temperature‐dependent current–voltage characteristics in dark condition indicates that the tunneling is the dominant carrier transport mechanism in our a‐Si:H‐based n/p‐type TRJ. The fabrication of a tandem cell structure consists of an a‐Si:H‐based top cell and an HIT‐type bottom cell with the a‐Si:H‐based n/p junction developed as a TRJ in between. The development of a‐Si:H‐based n/p junction as a TRJ leads to an improved a‐Si:H/HIT‐type tandem cell with a better open circuit voltage (V_oc), fill factor (FF), and efficiency. The improvements in the cell performance was attributed to the wider band‐tail states in the a‐Si:H(n) layer that helps to an enhanced tunneling and recombination process in the TRJ. The best photovoltage parameters of the tandem cell were found to be V_oc = 1430 mV, short circuit current density = 10.51 mA/cm², FF = 0.65, and efficiency = 9.75%. Copyright © 2015 John Wiley & Sons, Ltd.     

Highly transparent modulated surface textured front electrodes for high‐efficiency multijunction thin‐film silicon solar cells

To further increase the efficiency of multijunction thin‐film silicon (TF‐Si) solar cells, it is crucial for the front electrode to have a good transparency and conduction, to provide efficient light trapping for each subcell, and to ensure a suitable morphology for the growth of high‐quality silicon layers. Here, we present the implementation of highly transparent modulated surface textured (MST) front electrodes as light‐trapping structures in multijunction TF‐Si solar cells. The MST substrates comprise a micro‐textured glass, a thin layer of hydrogenated indium oxide (IOH), and a sub‐micron nano‐textured ZnO layer grown by low‐pressure chemical vapor deposition (LPCVD ZnO). The bilayer IOH/LPCVD ZnO stack guarantees efficient light in‐coupling and light trapping for the top amorphous silicon (a‐Si:H) solar cell while minimizing the parasitic absorption losses. The crater‐shaped micro‐textured glass provides both efficient light trapping in the red and infrared wavelength range and a suitable morphology for the growth of high‐quality nanocrystalline silicon (nc‐Si:H) layers. Thanks to the efficient light trapping for the individual subcells and suitable morphology for the growth of high‐quality silicon layers, multijunction solar cells deposited on MST substrates have a higher efficiency than those on single‐textured state‐of‐the‐art LPCVD ZnO substrates. Efficiencies of 14.8% (initial) and 12.5% (stable) have been achieved for a‐Si:H/nc‐Si:H tandem solar cells with the MST front electrode, surpassing efficiencies obtained on state‐of‐the‐art LPCVD ZnO, thereby highlighting the high potential of MST front electrodes for high‐efficiency multijunction solar cells. Copyright © 2015 John Wiley & Sons, Ltd.     

Back‐contacted back‐junction n‐type silicon solar cells featuring an insulating thin film for decoupling charge carrier collection and metallization geometry

In this study, back‐contacted back‐junction n‐type silicon solar cells featuring a large emitter coverage (point‐like base contacts), a small emitter coverage (point‐like base and emitter contacts), and interdigitated metal fingers have been fabricated and analyzed. For both solar cell designs, a significant reduction of electrical shading losses caused by an increased recombination in the non‐collecting base area on the rear side was obtained. Because the solar cell designs are characterized by an overlap of the B‐doped emitter and the P‐doped base with metal fingers of the other polarity, insulating thin films with excellent electrical insulation properties are required to prevent shunting in these overlapping regions. Thus, with insulating thin films, the geometry of the minority charge carrier collecting emitter diffusion and the geometry of the interdigitated metal fingers can be decoupled. In this regard, plasma‐enhanced chemical vapor deposited SiO₂ insulating thin films with various thicknesses and deposited at different temperatures have been investigated in more detail by metal‐insulator‐semiconductor structures. Furthermore, the influence of different metal layers on the insulation properties of the films has been analyzed. It has been found that by applying a SiO₂ insulating thin film with a thickness of more than 1000 nm and deposited at 350 °C to solar cells fabricated on 1 Ω cm and 10 Ω cm n‐type float‐zone grown silicon substrates, electrical shading losses could be reduced considerably, resulting in excellent short‐circuit current densities of more than 41 mA/cm² and conversion efficiencies of up to 23.0%. Copyright © 2012 John Wiley & Sons, Ltd.     

Deposition of highly efficient microcrystalline silicon solar cells under conditions of low H2 dilution: the role of the transient depletion induced incubation layer

This paper addresses the plasma deposition of highly efficient microcrystalline silicon (μc‐Si:H) p‐i‐n solar cells under conditions of high SiH₄ utilization and low H₂ dilution. It was established that the transient depletion of the initially present SiH₄ source gas induces the formation of an amorphous incubation layer that prevents successful crystallite nucleation in the i‐layer and leads to poor solar cell performance. The effect of this transient depletion induced incubation layer on solar cells was made visible through dedicated solar cell deposition series and selected area electron diffraction measurements. Applying a gas flow procedure at plasma ignition it was succeeded to prepare state‐of‐the‐art μc‐Si:H material and solar cells under low hydrogen dilution conditions, highlighted by μc‐Si:H solar cells of up to 9·5% efficiency prepared using an undiluted source gas flow consisting solely of SiH₄. Copyright © 2007 John Wiley & Sons, Ltd.     

Simulation and fabrication of heterojunction silicon solar cells from numerical computer and hot‐wire CVD

In this paper, we will present a Pc1D numerical simulation for heterojunction (HJ) silicon solar cells, and discuss their possibilities and limitations. By means of modeling and numerical computer simulation, the influence of emitter‐layer/intrinsic‐layer/crystalline‐Si heterostructures with different thickness and crystallinity on the solar cell performance is investigated and compared with hot wire chemical vapor deposition (HWCVD) experimental results. A new technique for characterization of n‐type microcrystalline silicon (n‐µc‐Si)/intrinsic amorphous silicon (i‐a‐Si)/crystalline silicon (c‐Si) heterojunction solar cells from Pc1D is developed. Results of numerical modeling as well as experimental data obtained using HWCVD on µc‐Si (n)/a‐Si (i)/c‐Si (p) heterojunction are presented. This work improves the understanding of HJ solar cells to derive arguments for design optimization. Some simulated parameters of solar cells were obtained: the best results for J_sc = 39·4 mA/cm², V_oc = 0·64 V, FF = 83%, and η = 21% have been achieved. After optimizing the deposition parameters of the n‐layer and the H₂ pretreatment of solar cell, the single‐side HJ solar cells with J_sc = 34·6 mA/cm², V_oc = 0·615 V, FF = 71%, and an efficiency of 15·2% have been achieved. The double‐side HJ solar cell with J_sc = 34·8 mA/cm², V_oc = 0·645 V, FF = 73%, and an efficiency of 16·4% has been fabricated. Copyright © 2009 John Wiley & Sons, Ltd.