Fabrication and characteristics of n-Si/c-Si/p-Si heterojunction solar cells using hot-wire CVD

A double-side (bifacial) heterojunction (HJ) Si solar cell was fabricated using hot-wire chemical vapor deposition. The properties of n-type, intrinsic and p-type Si films were investigated. In these devices, the doped microcrystalline Si layers (n-type Si for emitter and p-type Si for back contact) are combined with and without a thin intrinsic amorphous Si buffer layer. The maximum temperature during the whole fabrication process was kept below 150 °C. The influence of hydrogen pre-treatment and n-Si emitter thickness on performance of solar cells have been studied. The best bifacial Si HJ solar cell (1 cm² sample) with an intrinsic layer yielded an active area conversion efficiency of 16.4% with an open circuit voltage of 0.645 V, short circuit current of 34.8 mA/cm² and fill factor of 0.73.     

High‐Efficiency Nonfullerene Organic Solar Cells with a Parallel Tandem Configuration

In this work, a highly efficient parallel connected tandem solar cell utilizing a nonfullerene acceptor is demonstrated. Guided by optical simulation, each of the active layer thicknesses of subcells are tuned to maximize its light trapping without spending intense effort to match photocurrent. Interestingly, a strong optical microcavity with dual oscillation centers is formed in a back subcell, which further enhances light absorption. The parallel tandem device shows an improved photon‐to‐electron response over the range between 450 and 800 nm, and a high short‐circuit current density (J _SC) of 17.92 mA cm^?2. In addition, the subcells show high fill factors due to reduced recombination loss under diluted light intensity. These merits enable an overall power conversion efficiency (PCE) of >10% for this tandem cell, which represents a ≈15% enhancement compared to the optimal single‐junction device. Further application of the designed parallel tandem configuration to more efficient single‐junction cells enable a PCE of >11%, which is the highest efficiency among all parallel connected organic solar cells (OSCs). This work stresses the importance of employing a parallel tandem configuration for achieving efficient light harvesting in nonfullerene‐based OSCs. It provides a useful strategy for exploring the ultimate performance of organic solar cells.     

Infrared Solution‐Processed Quantum Dot Solar Cells Reaching External Quantum Efficiency of 80% at 1.35 µm and Jsc in Excess of 34 mA cm−2

Developing low‐cost photovoltaic absorbers that can harvest the short‐wave infrared (SWIR) part of the solar spectrum, which remains unharnessed by current Si‐based and perovskite photovoltaic technologies, is a prerequisite for making high‐efficiency, low‐cost tandem solar cells. Here, infrared PbS colloidal quantum dot (CQD) solar cells employing a hybrid inorganic–organic ligand exchange process that results in an external quantum efficiency of 80% at 1.35 µm are reported, leading to a short‐circuit current density of 34 mA cm^?2 and a power conversion efficiency (PCE) up to 7.9%, which is a current record for SWIR CQD solar cells. When this cell is placed at the back of an MAPbI₃ perovskite film, it delivers an extra 3.3% PCE by harnessing light beyond 750 nm.     

Hybrid Si microwire and planar solar cells: passivation and characterization

We report an efficient hybrid Si microwire (radial junction) and planar solar cell with a maximum efficiency of 11.0% under AM 1.5G illumination. The maximum efficiency of the hybrid cell is improved from 7.2% to 11.0% by passivating the top surface and p-n junction with thin a-SiN:H and intrinsic poly-Si films, respectively, and is higher than that of planar cells of the identical layers due to increased light absorption and improved charge-carrier collections in both wires and planar components.     

Hot-wire CVD deposited n-type μc-Si films for μc-Si/c-Si heterojunction solar cell applications

Phosphorous-doped microcrystalline silicon (μc-Si) films were prepared using hot-wire chemical vapor deposition (HWCVD). Structural, electrical and optical properties of these thin films were systematically studied as a function of PH₃ gas mixture ratio. We report recent results for p-type crystalline silicon-based heterojunction (HJ) solar cells using the HWCVD n-μc-Si film to form an n-p junction. The surface morphology of the crystalline Si substrate after hydrogen treatment was examined using atomic force microscopy. A transfer length method was used to modify the indium-tin-oxide (ITO) deposition parameters in order to reduce front ITO/n-μc-Si contact resistance. In our best solar cell sample (1 cm²) without any buffer layer, the conversion efficiency of 15.1% has been achieved with an open circuit voltage of 0.615 V, fill factor of 0.71 and short circuit current density of 34.6 mA/cm² under 100 mW/cm² condition. The spectral response of this cell will also be discussed.     

Amide‐Catalyzed Phase‐Selective Crystallization Reduces Defect Density in Wide‐Bandgap Perovskites

Wide‐bandgap (WBG) formamidinium–cesium (FA‐Cs) lead iodide–bromide mixed perovskites are promising materials for front cells well‐matched with crystalline silicon to form tandem solar cells. They offer avenues to augment the performance of widely deployed commercial solar cells. However, phase instability, high open‐circuit voltage (V_oc) deficit, and large hysteresis limit this otherwise promising technology. Here, by controlling the crystallization of FA‐Cs WBG perovskite with the aid of a formamide cosolvent, light‐induced phase segregation and hysteresis in perovskite solar cells are suppressed. The highly polar solvent additive formamide induces direct formation of the black perovskite phase, bypassing the yellow phases, thereby reducing the density of defects in films. As a result, the optimized WBG perovskite solar cells (PSCs) (E_g ≈ 1.75 eV) exhibit a high V_oc of 1.23 V, reduced hysteresis, and a power conversion efficiency (PCE) of 17.8%. A PCE of 15.2% on 1.1 cm² solar cells, the highest among the reported efficiencies for large‐area PSCs having this bandgap is also demonstrated. These perovskites show excellent phase stability and thermal stability, as well as long‐term air stability. They maintain ≈95% of their initial PCE after 1300 h of storage in dry air without encapsulation.     

Minimizing the Carrier Collection Loss of the Neutral-Color Transparent Crystalline-silicon Solar Modules via Hybrid Electrode Design

Transparent solar cells can be used where conventional solar cells are inapplicable, such as, in glass windows of buildings; however, reports on modularization, which is essential for their commercialization, are scarce. Here, a novel modularization method has been proposed for the fabrication of transparent solar cells and a 100-cm² neutral-color transparent crystalline-silicon solar module has been developed using a hybrid electrode comprising a microgrid electrode and an edge busbar electrode. The transparent solar module exhibits a power conversion efficiency (PCE) of 11.94 and 13.14% when connected in series and in parallel, respectively, with an average visible transmittance of 20%. Additionally, the module exhibits negligible losses in PCE (lower than 0.23%) in outdoor, mechanical-load, and damp-heat (at 85°C/85% RH) stability tests, indicating high stability. The transparent solar module proposes here could facilitate the commercialization of transparent solar cells.     

Development of new materials for solar cells in Nagoya Institute of Technology

Solar cells with high efficiency and low price have long been desired, however, the commercially available solar cells are still expensive and the efficiencies of them are not high enough yet. A tandem solar cell was fabricated to develop a high-efficiency solar cell, and amorphous carbon solar cells were fabricated to develop a low-price solar cell.An AlGaAs/Si tandem solar cell was successfully fabricated by heteroepitaxial growth of AlGaAs on Si substrate. At first, a p–n junction was formed in Si substrate by the impurity diffusion method. Then, an AlGaAs p–n junction was grown by MOCVD. Since the AlGaAs p–n junction has a graded band gap emitter, the photo-excited minority carriers can be collected efficiently. The energy conversion efficiency of AlGaAs/Si tandem solar cell was 21.4% (AM0) in spite of large lattice mismatch and difference in thermal expansion coefficients between AlGaAs and Si.Solar cells were fabricated by using amorphous carbon films deposited by Ion Beam Sputtering and Pulse Laser Deposition (PLD). The highest efficiency of 1.82% (AM0) was attained with a-C(IBS)/p-C(pyrolysis)/p-Si structure. Solar cells using a-C:H were also fabricated by PLD and Plasma CVD, and the efficiencies of them were 2.1% (AM1.5) and 0.04% (AM0), respectively.Other research activities on solar cells in Nagoya Institute of Technology are briefly mentioned.     

Development of a hot-wire chemical vapor deposition n-type emitter on p-type crystalline Si-based solar cells

We have developed a p-type, crystalline Si-based solar cell using hot-wire chemical vapor deposition (HWCVD) n-type microcrystalline Si to form an n-p junction (emitter). The CVD process was rapid and a low substrate temperature was used. The p-type Czochralski (CZ) c-Si wafer has a thickness of 400 μm and has a thermally diffused Al back-field contact. Before forming the n-p junction, the front surface of the p-type c-Si was cleaned using a diluted HF solution to remove the native oxides. The n-type emitter was formed at 220 °C by depositing 50 Å a-Si:H and then a 100 Å μc-Si n-layer. The total deposition time to form the emitter was less than 1 min. The top contact of the device is a lithograph defined and isolated 1×1 cm² and 780 Å indium tin oxides (ITO) with metal fingers on top. Our best solar cell conversion efficiency is 13.3% with V_oc of 0.58 V, FF of 0.773, and J_sc of 29.86 mA cm⁻² under one-sun condition. Quantum efficiency (QE) measurement on this solar cell shows over 90% in the region between 540 and 780 nm, but poor response in the blue and deep red. We find that the ITO top contact that acts as an antireflection layer increases the QE in the middle region. To improve the device efficiency further, J_sc needs to be increased. Better emitter and light trapping will be developed in future work. The cell shows no degradation after 1000 h of standard light soaking.     

GaP/GaNP Heterojunctions for Efficient Solar‐Driven Water Oxidation

The growth and characterization of an n‐GaP/i‐GaNP/p⁺‐GaP thin film heterojunction synthesized using a gas‐source molecular beam epitaxy (MBE) method, and its application for efficient solar‐driven water oxidation is reported. The TiO₂/Ni passivated n‐GaP/i‐GaNP/p⁺‐GaP thin film heterojunction provides much higher photoanodic performance in 1 m KOH solution than the TiO₂/Ni‐coated n‐GaP substrate, leading to much lower onset potential and much higher photocurrent. There is a significant photoanodic potential shift of 764 mV at a photocurrent of 0.34 mA cm^?2, leading to an onset potential of ≈0.4 V versus reversible hydrogen electrode (RHE) at 0.34 mA cm^?2 for the heterojunction. The photocurrent at the water oxidation potential (1.23 V vs RHE) is 1.46 and 7.26 mA cm^?2 for the coated n‐GaP and n‐GaP/i‐GaNP/p⁺‐GaP photoanodes, respectively. The passivated heterojunction offers a maximum applied bias photon‐to‐current efficiency (ABPE) of 1.9% while the ABPE of the coated n‐GaP sample is almost zero. Furthermore, the coated n‐GaP/i‐GaNP/p⁺‐GaP heterojunction photoanode provides a broad absorption spectrum up to ≈620 nm with incident photon‐to‐current efficiencies (IPCEs) of over 40% from ≈400 to ≈560 nm. The high low‐bias performance and broad absorption of the wide‐bandgap GaP/GaNP heterojunctions render them as a promising photoanode material for tandem photoelectrochemical (PEC) cells to carry out overall solar water splitting.     

Roll-Pressed Silicon Anodes with High Reversible Volumetric Capacity Achieved by Interfacial Stabilization and Mechanical Strengthening of a Silicon/Graphene Hybrid Assembly

Application of Si anodes is hindered by severe capacity fading due to pulverization of Si particles during the large volume changes of Si during charge/discharge and repeated formation of the solid-electrolyte interphase. To address these issues, considerable efforts have been devoted to the development of Si composites with conductive carbons (Si/C composites). However, Si/C composites with high C content inevitably show low volumetric capacity because of low electrode density. For practical applications, the volumetric capacity of a Si/C composite electrode is more important than gravimetric capacity, but volumetric capacity in pressed electrodes is rarely reported. Herein, a novel synthesis strategy is demonstrate for a compact Si nanoparticle/graphene microspherical assembly with interfacial stability and mechanical strength achieved by consecutively formed chemical bonds using 3-aminopropyltriethoxysilane and sucrose. The unpressed electrode (density: 0.71 g cm⁻³) shows a reversible specific capacity of 1470 mAh g⁻¹ with a high initial coulombic efficiency of 83.7% at a current density of 1 C-rate. The corresponding pressed electrode (density: 1.32 g cm⁻³) exhibits high reversible volumetric capacity of 1405 mAh cm⁻³ and gravimetric capacity of 1520 mAh g⁻¹ with a high initial coulombic efficiency of 80.4% and excellent cycling stability of 83% over 100 cycles at 1 C-rate.     

Enhancing the Performance of Polymer Solar Cells via Core Engineering of NIR‐Absorbing Electron Acceptors

In order to utilize the near‐infrared (NIR) solar photons like silicon‐based solar cells, extensive research efforts have been devoted to the development of organic donor and acceptor materials with strong NIR absorption. However, single‐junction organic solar cells (OSCs) with photoresponse extending into >1000 nm and power conversion efficiency (PCE) >11% have rarely been reported. Herein, three fused‐ring electron acceptors with varying core size are reported. These three molecules exhibit strong absorption from 600 to 1000 nm and high electron mobility (>1 × 10^?3 cm² V^?1 s^?1). It is proposed that core engineering is a promising approach to elevate energy levels, enhance absorption and electron mobility, and finally achieve high device performance. This approach can maximize both short‐circuit current density ( J_SC) and open‐circuit voltage (V_OC) at the same time, differing from the commonly used end group engineering that is generally unable to realize simultaneous enhancement in both V_OC and J_SC. Finally, the single‐junction OSCs based on these acceptors in combination with the widely polymer donor PTB7‐Th yield J_SC as high as 26.00 mA cm^?2 and PCE as high as 12.3%.     

Efficient Semitransparent Solar Cells with High NIR Responsiveness Enabled by a Small‐Bandgap Electron Acceptor

Inspired by the remarkable promotion of power conversion efficiency (PCE), commercial applications of organic photovoltaics (OPVs) can be foreseen in near future. One of the most promising applications is semitransparent (ST) solar cells that can be utilized in value‐added applications such as energy‐harvesting windows. However, the single‐junction STOPVs utilizing fullerene acceptors show relatively low PCEs of 4%–6% due to the limited sunlight absorption because it is a dilemma that more photons need to be harvested in UV–vis–near‐infrared (NIR) region to generate high photocurrent, which leads to the significant reduction of device transparency. This study describes the development of a new small‐bandgap electron‐acceptor material ATT‐2, which shows a strong NIR absorption between 600 and 940 nm with an E _g^opt of 1.32 eV. By combining with PTB7‐Th, the as‐cast OPVs yield PCEs of up to 9.58% with a fill factor of 0.63, an open‐circuit voltage of 0.73 V, and a very high short‐circuit current of 20.75 mA cm^?2. Owing to the favorable complementary absorption of low‐bangap PTB7‐Th and small‐bandgap ATT‐2 in NIR region, the proof‐of‐concept STOPVs show the highest PCE of 7.7% so far reported for single‐junction STOPVs with a high transparency of 37%.     

Embedded Nickel-Mesh Transparent Electrodes for Highly Efficient and Mechanically Stable Flexible Perovskite Photovoltaics: Toward a Portable Mobile Energy Source

The rapid development of Internet of Things mobile terminals has accelerated the market's demand for portable mobile power supplies and flexible wearable devices. Here, an embedded metal-mesh transparent conductive electrode (TCE) is prepared on poly(ethylene terephthalate) (PET) using a novel selective electrodeposition process combined with inverted film-processing methods. This embedded nickel (Ni)-mesh flexible TCE shows excellent photoelectric performance (sheet resistance of ≈0.2–0.5 Ω sq⁻¹ at high transmittance of ≈85–87%) and mechanical durability. The PET/Ni-mesh/polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS PH1000) hybrid electrode is used as a transparent electrode for perovskite solar cells (PSCs), which exhibit excellent electric properties and remarkable environmental and mechanical stability. A power conversion efficiency of 17.3% is obtained, which is the highest efficiency for a PSC based on flexible transparent metal electrodes to date. For perovskite crystals that require harsh growth conditions, their mechanical stability and environmental stability on flexible transparent embedded metal substrates are studied and improved. The resulting flexible device retains 76% of the original efficiency after 2000 bending cycles. The results of this work provide a step improvement in flexible PSCs.     

A Small‐Molecule “Charge Driver” enables Perovskite Quantum Dot Solar Cells with Efficiency Approaching 13%

Halide perovskite colloidal quantum dots (CQDs) have recently emerged as a promising candidate for CQD photovoltaics due to their superior optoelectronic properties to conventional chalcogenides CQDs. However, the low charge separation efficiency due to quantum confinement still remains a critical obstacle toward higher‐performance perovskite CQD photovoltaics. Available strategies employed in the conventional CQD devices to enhance the carrier separation, such as the design of type‐Ⅱ core–shell structure and versatile surface modification to tune the electronic properties, are still not applicable to the perovskite CQD system owing to the difficulty in modulating surface ligands and structural integrity. Herein, a facile strategy that takes advantage of conjugated small molecules that provide an additional driving force for effective charge separation in perovskite CQD solar cells is developed. The resulting perovskite CQD solar cell shows a power conversion efficiency approaching 13% with an open‐circuit voltage of 1.10 V, short‐circuit current density of 15.4 mA cm^?2, and fill factor of 74.8%, demonstrating the strong potential of this strategy toward achieving high‐performance perovskite CQD solar cells.     

Towards an all-polymer cathode for dye sensitized photovoltaic cells

Highly conducting conjugated polymer composite was deposited by vapour phase polymerization. Poly[3,4-ethylenedioxythiophene:para-toluenesulfonate] (PEDOT:PTS) itself was used as the counter electrode in a dye sensitized solar cell. The maximum photocurrent of 9.7 mA/cm², open circuit voltage of 759 mV, fill factor of 0.71 with a power conversion efficiency of 5.25% were observed for glass based wet type dye sensitized solar cell, under illumination of 100 mW/cm². It was observed that the resistance, during operation of the dye sensitized solar cells, due to the I₃⁻ conversion was less with PEDOT:PTS coated cathodes than with standard platinum coated fluorine doped tin oxide and was confirmed by steady state electrochemical measurements.     

13.7% Efficiency Small‐Molecule Solar Cells Enabled by a Combination of Material and Morphology Optimization

Compared with the quick development of polymer solar cells, achieving high‐efficiency small‐molecule solar cells (SMSCs) remains highly challenging, as they are limited by the lack of matched materials and morphology control to a great extent. Herein, two small molecules, BSFTR and Y6, which possess broad as well as matched absorption and energy levels, are applied in SMSCs. Morphology optimization with sequential solvent vapor and thermal annealing makes their blend films show proper crystallinity, balanced and high mobilities, and favorable phase separation, which is conducive for exciton dissociation, charge transport, and extraction. These contribute to a remarkable power conversion efficiency up to 13.69% with an open‐circuit voltage of 0.85 V, a high short‐circuit current of 23.16 mA cm^?2 and a fill factor of 69.66%, which is the highest value among binary SMSCs ever reported. This result indicates that a combination of materials with matched photoelectric properties and subtle morphology control is the inevitable route to high‐performance SMSCs.     

Simulation of characteristics of double-junction solar cells based on ZnSiP2 heterostructures on silicon substrate

Design and operation modes of double-junction monolithic lattice-matched solar cells based on the ZnSiP₂/Si system of materials have been calculated. The effect of the photoactive region thickness and minority carrier lifetime in ZnSiP₂ layers on the efficiency of conversion of the incident solar light energy into electrical power was determined. It is shown that solar cells based on ZnSiP₂/Si heterostructures can provide efficiencies of 28.8% at AM1.5D, 100 mW/cm², and 33.3% at AM1.5D, 200 W/cm².     

掺(Ga,Si)银铝浆对n型TOPCon太阳能电池电性能的影响

银铝浆是新一代太阳能电池(n型TOPCon)的关键材料,但其金属化后在Si发射极表面形成很大且很深的“银铝尖钉”,尖钉易击穿p-n结造成短路,成为限制其应用的瓶颈。引入Si、Ga元素对银铝浆进行优化,分别制备了掺Si和掺Ga, Si的银铝浆,研究其对金属化区域暗态饱和电流密度J_0.metal、欧姆接触电阻R_c的影响机制。结果表明：掺入少量Si后,金属化区域未见明显“银铝尖钉”,说明掺Si后抑制了在浆料金属化时出现“银铝尖钉”的现象,对p-n结损伤较小,J_0.metal下降,开路电压V_oc上升,但是R_c增大。再掺入Ga组分后“银铝尖钉”明显变浅,数量变多,R_c下降,弥补了掺Si银铝浆欧姆接触差的弊端,有较高的电池转换效率;用扩散浓度测试仪(ECV)对发射极表层进行元素浓度分析,发现Ga分布于表层0～50 nm处,有利于改善欧姆接触。研究了Ga、Si的掺入量对银铝浆电性能的影响,电池转换效率最高达到24.68%,太阳能电池效率提升0.55%。     

Fabrication of selective-emitter silicon heterojunction solar cells using hot-wire chemical vapor deposition and laser doping

The Si heterojunction (HJ) solar cells were fabricated on the textured p-type mono-crystalline Si (c-Si) substrates using hot-wire chemical vapor deposition (HWCVD). In view of the potential for the bottom cell in a hybrid junction structure, the microcrystalline Si (μc-Si) film was used as the emitter with various PH₃ dilution ratios. Prior to the n-μc-Si emitter deposition, a 5 nm-thick intrinsic amorphous Si layer (i-a-Si) was grown to passivate the c-Si surface. In order to improve the indium-tin oxide (ITO)/emitter front contact without using the higher PH₃ doping concentration, a laser doping technique was employed to improve the ITO/n-μc-Si contact via the formation of the selective emitter structure. For a cell structure of Ag grid/ITO/n-μc-Si emitter/i-a-Si/textured p-c-Si/Al-electrode, the conversion efficiency (AM1.5) can be improved from 13.25% to 14.31% (cell area: 2 cm × 2 cm) via a suitable selective laser doping process.