In this work, an n-type high performance multicrystalline silicon (nHPMC) ingot (τ >1.2 ms) was cast at NTNU. A new method to manufacture nHPMC solar cells with hetero junction solar cell architecture is presented. Texturing of the wafers is performed through silver assisted chemical etching followed by an alkaline solution treatment process. The slight differences of the reactions between the concentration of the alkali solutions and the nanopores on silicon surface has been determined and used to tailor different textures. Alkaline solutions with gradient concentration were developed to improve the surface morphology for HIT solar cells after a silver assisted chemical etching process. A homogeneous texture with quasi pyramid morphology was then obtained through balancing the reflectance and surface properties on nHPMC wafers. This kind of quasi pyramid texture is also a good starting point for the surface passivation during HIT processes. An efficiency of 19.03% has been obtained, demonstrating the potential of using n-type HPMC in the production of cost effective solar cells.

n-type CZ-Si wafers featuring longer minority carrier lifetime and higher tolerance of certain metal contamination can offer one of the best Si-based solar cells. In this study, Si heterojuction (SHJ) solar cells which was fabricated with different wafers in the top, middle and tail positions of the ingot, exhibited a stable high efficiency of > 22% in spite of the various profiles of the resistivity and lifetime, which demonstrated the high material utilization of n-type ingot. In addition, for effectively converting the sunlight into electrical power, the pyramid size, pyramid density and roughness of surface of the Cz-Si wafer were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). Furthermore, the dependence of SHJ solar cell open-circuit voltage on the surface topography was discussed, which indicated that the uniformity of surface pyramid helps to improve the open-circuit voltage and conversion efficiency. Moreover, the simulation revealed that the highest efficiency of the SHJ solar cell could be achieved by the wafer with a thickness of 100 μm. Fortunately, over 23% of the conversion efficiency of the SHJ solar cell with a wafer thickness of 100 μm was obtained based on the systematic optimization of cell fabrication process in the pilot production line. Evidently, the large availability of both n-type ingot and thinner wafer strongly supported the lower cost fabrication of high efficiency SHJ solar cell.

•Highly crystalline ITO films were fabricated using reactive plasma deposition (RPD) method at room temperature.•The initial growth model was transformed from 3D to 2D depending on oxygen partial pressure.•High optical transmittance (90%) and low electrical resistivity (2.3×10−4 Ω cm) ITO films have been developed.•ITO film presented various metal-semiconductor transition temperatures from 90 K to 175 K.Highly crystalline indium tin oxide (ITO) films were fabricated by reactive plasma deposition (RPD) technique at room temperature. The effects of oxygen partial pressure on structural, optical and electrical properties of the ITO film were investigated. An interesting growth mode transition from 3 dimensions (3D) to 2 dimensions (2D) was observed. It was found that this transition in growth mode was accompanied by a phase change from amorphous to crystalline. In addition, the obtained ITO film showed a metal-semiconductor transition property with various transition temperatures from 90 K to 175 K. By optimizing oxygen partial pressure value, film with low resistivity of 2.3×10−4 Ω cm, carrier mobility high up to 35 cm2/V s and average optical transmittance over 90% was developed at room temperature.

•The band gap of CIGSeS thin film is tuned by simultaneous H2Se/H2S reaction.•S content in CIGSeS film is increased by increasing H2S/H2Se concentration ratio.•CIGSeS film is Ga-poor and S-poor during the initial H2S/H2Se reaction.•Ga and S incorporation into CIGSeS is realized during the 600 °C H2S/H2Se reaction.The simultaneous selenization/sulfurization is investigated to fabricate Cu(In, Ga)(Se,S)2 thin films in the H2S/H2Se/N2 hybrid gas, and the optical band gap of Cu(In, Ga)(Se,S)2 thin film is adjusted from 1.05 eV to 1.22 eV by varying the concentration ratio of H2S/H2Se. It is found that more S incorporates into the CIGSeS phase when the H2S concentration is increased, which widens the band gap of CIGSeS alloy. Furthermore, the through-film element profile of the CIGSeS films with different reaction time reveals that CIGSeS film is Ga-poor and S-poor during the initial reaction, and Ga and S are redistributed during the subsequent reaction with a joint of H2S and H2Se.

•IWO with high mobility and high transmittance was fabricated at low temperature.•Oxygen pressure plays the key role in the property of IWO films by RPD technique.•The IWO films can act as both TCO and ARC of SHI solar cell.•20.8% of efficiency for SHI solar cell was obtained with the optimized IWO films.W-doped In2O3 transparent conductive film was developed at a low substrate temperature of 200 °C by reactive plasma deposition technique for the applications to silicon heterojunction solar cell. The maximum Hall mobility of 89 cm2/V s with a corresponding carrier concentration of 1.6×1020 cm−3 was achieved at a relatively high oxygen partial pressure of 7.2×10−4 Torr without any special treatment. According to the Hall effect measurements at variable temperature from 80 K to 300 K, high Hall mobility was mainly attributed to the ionized impurity scattering, neutral impurity scattering and phonon scattering, grain boundary scattering only plays the minor role in the carrier transportation of IWO film in this work. Additionally, XRD results show the samples have a cubic phase of bixbyite-type In2O3 polycrystalline structure with a preferential orientation of (222) plane. The plasma wavelength of larger than 2.3 μm is very beneficial for sunlight transparency. Consequently, IWO is applied to a-Si/c-Si heterojunction solar cells, 20.8% of conversion efficiency has been obtained under the optimized experimental conditions.

•The n-type HIT solar cell was studied by AFORS-HET software.•Fermi level is more reasonable than doping concentration to evaluate solar cells.•The physical mechanisms of Voc and FF for HIT solar cells were investigated.•Fermi levels and band offsets were optimized for over 25% efficiency solar cells.The heterojunction with intrinsic thin-layer (HIT) solar cell has reached a record conversion efficiency of 24.7% on a 98 μm wafer recently. But the physical mechanism of this solar cell is not understood clearly. In this work, the roles of Fermi level of doped a-Si:H and band offsets at the a-Si:H/c-Si interface in HIT solar cell were studied through computer simulation. With the increasing of the doping concentration in the emitter and back surface field, the Fermi levels get closer to the band edge and more defects are produced. This simulation shows that for over 25% conversion efficiency solar cell, the value of Ef − Ev in a-Si:H(p) layer should be less than 250 meV, Ef of a-Si:H(n) layer should be as close as possible to the conduction band edge. Furthermore, the band discontinuities at the front a-Si:H/c-Si interface could lead to a sharp decline of the fill factor when the valence band offset is larger than 0.55 eV. However, the conduction band offset makes little impacts on the solar cell performance unless the bandgap of a-Si:H is small than 1.62 eV. As a result, the highest efficiency of 25.21% is obtained by the optimized parameters.Graphical abstract