Passivation of n-type and p-type monocrystalline CZ Si wafers (both polished and textured) with silicon oxide layers prepared by thermal (TO), chemical (CO) and plasma (PO) techniques have been extensively investigated from the measurement of minority carrier lifetime (tau) by transient electrical photo-response method, density of interface states (N-SS) measurement by capacitance - voltage study and silicon oxidation states by X-ray photoelectron spectroscopy (XPS) study of the SiO2/Si interface. It has been observed that N-SS and tau have an inverse relation but the dependence is not linear. The method (TO, CO or PO) of oxide layer development has been found to play a crucial role to control the passivation of the c-Si wafer surface. It has been observed that the thermally grown oxide layer (TO) is superior among three oxide layers for all the different c-Si surfaces. Very low density of interface states (<5 x 10(11)) were found in both p-type and n-type polished wafer passivated with TO layer. Highest lifetimes of 170 mu s for n-type polished wafer and 102.74 mu s for p-type polished wafer were obtained with TO. The amount of sub oxide formed at the interface of both n- and p-type of wafers during different oxidation process, may have some correlation with N-SS which in turn determines the passivation quality of the wafers. Improvement of implied V-OC for both polished and textured wafers (n-type and p-type) was found using thermally grown oxide with respect to others.

Passivated emitter rear contact (PERC) solar cell involves upgraded adaptation of technology over the existing silicon wafer-based aluminium back surface field (Al-BSF) solar cell. The lower efficiency of Al-BSF is caused by a few drawbacks e.g. higher rear surface recombination and weaker electric field at the rear surface. These technical shortcomings can be mitigated by incorporating field-effect passivation (FEP) layer viz. aluminium oxide (Al2O3) at the rear surface with a capping layer of SiNX on it. Conventionally two new processing steps utilizing two expensive equipments, green laser (532 nm) for laser ablation of the FEP and SiNX capping layer stack at the rear surface and single side etcher for rear side polishing of wafer are used for manufacturing of PERC cells. In this paper, we have shown that instead of these two new expensive processing equipments we can use the IR laser (1024 nm) and RIE etcher, which are commonly available for Al-BSF manufacturing line, for the fabrication of PERC solar cells. Using p-type wafers of rather modest quality (minority carrier lifetime of ≥10 µs) we have demonstrated improvement of the efficiency from 18.71 to 19.62% and enhancements in VOC and JSC from 628 to 646 mV and 38.59 mA/cm2 to 39.82 mA/cm2, respectively. A thorough root-cause analysis has been carried out to optimize the two new approaches within the existing Al-BSF line for the fabrication of PERC solar cell.

In last few decades the study of zinc oxide (ZnO) nanoparticles established the fact that, they have wide range of high technology applications. Among all the nanoparticles ZnO nanorods have been widely used due to their ease of formation and applications. Here, nitrogen doped (N-doped) ZnO nanorods have been developed by hydrothermal method. The layer of N-doped ZnO nanorods along with crystalline silicon (c-Si) wafer forms a heterojunction Si solar cell. It has minimum reflectance and good light trapping effect. Hence, no need to use another layer for ARC. The use of this layer provides an efficiency enhancement.

Higher price-per-watt of silicon (Si) solar cells is still the main bottleneck in their widespread use for power generation due to their expensive manufacturing process. The n-type zinc oxide (n-ZnO) and p-type Si (p-Si) based single heterojunction solar cell is one of the several methods being tried to replace conventional Si single homojunction solar cell technology. In this work, we have explored the possibility of producing photovoltaic materials by employing RF sputtering and hydrothermal technologies. Conductivity of ZnO nanorods has been increased by aluminium (Al) doping. The advantages of using Al doped ZnO (AZO) nanorods (NRs) have been investigated. The integrated reflectance (IR) has been found to be only ~2.86%. Hence, the short circuit current density (Jsc) has been increased by minimizing the reflection loss of solar cells. AZO NR array have been developed over several large area (3″ × 3″) textured p-Si wafers to confirm the repeatability. The maximum efficiency of AZO NRs/Si solar cell of 0.8 cm2 area has been found to be 6.25% for textured p-type Si wafer which is much higher than reported hitherto for this type of solar cell. A simple, low temperature, low cost procedure is thus being proposed, which has the potential of attaining lower cost of production of heterojunction silicon solar cells.

Antireflection coatings play an important role in enhancing the performance of crystalline silicon solar cells by increasing the light coupling into the active region of the devices. In this work we investigated the effects of seed layer thickness and growth time on the reflection properties of solution-grown zinc oxide nanowhiskers. Our results reveal the potential of zinc oxide nanowhiskers as antireflection coating in crystalline silicon solar cells as investigated herein. With this efficient antireflection coating, we have presented a hierarchical structure integrating zinc oxide nanowhisker arrays on silicon micropyramids for improving the energy conversion efficiency. This structure displays broadband reflection suppression in the 300–1200 nm range, with an integrated reflectance of 2.28%. A conversion efficiency of 13.3% was obtained, which is significantly high for large area (3″ × 3″) solar cell fabricated using zinc oxide nanowhiskers as the antireflection coating layer.

In order to increase the efficiency of silicon based Thin Film Solar (TFS) cells, it is necessary to use better light management techniques. Texturization of sputtered aluminium doped zinc oxide (Al:ZnO or AZO) films has opened up a variety of ways for optimization of light trapping schemes. Here, AZO has been etched with acid as well as alkali. A difference in optical and electrical characteristics of acid and alkali etched AZO has been observed. By etching AZO with potassium hydroxide (KOH), 82% transmittance (in the visible range), high rms roughness and ∼13Ω/□ sheet resistance have been achieved.

In order to increase the stabilized efficiencies of thin film silicon (TFS) solar cells it is necessary to use better light management techniques. Texturization by etching of sputtered aluminum doped zinc oxide (Al:ZnO or AZO) films has opened up a variety of promises to optimize light trapping schemes. RF sputtered AZO film has been etched by potassium hydroxide (KOH). A systematic study of etching conditions such as etchant concentration, etching time, temperature management etc. have been performed in search of improved electrical and optical performances of the films. The change in etching conditions has exhibited a noticeable effect on the structure of AZO films for which the light trapping effect differs. After optimizing the etching conditions, nanorods have been found on the substrate. Hence, nanorods have been developed only by chemical etching, rather than the conventional development method (hydrothermal method, sol-gel method, electrolysis method etc.). The optimized etched substrate has 82% transmittance, moderate haze in the visible range and sheet resistance ∼13 (Ω/□). The developed nanorods (optimized etched substrate) provide better light trapping within the cell as the optical path length has been increased by using the nanorods. This provides an effect on carrier collection as well as the efficiency in a-Si solar cells. Finite difference time domain (FDTD) simulations have been performed to observe the light trapping by AZO nanorods formed on sputtered AZO films. For a p-i-n solar cell developed on AZO nanorods coated with sputtered AZO films, it has been found through simulations that, the incident light is back scattered into the absorbing layer, leading to an increase in photogenerated current and hence higher efficiency. It has been found that, the light that passes through the nanorods is not getting absorbed and maximum amount of light is back scattered towards the solar cell.

As-deposited sputtered ZnO:Al (AZO) thin films having high transparency (T ≥ 85% at 550 nm of wavelength) and good electrical properties (ρ = 2.59 × 10−04 Ω cm) are etched to get suitable light trapping in thin film solar cells, using reactive ion etching method in sulfur hexafluoride–argon (SF6/Ar) plasma and trifluoromethane–argon (CHF3/Ar) plasma to texture their surface. Though the electrical properties of the films are not affected much by the etching process but significant increment in the average haze values in the wave length range of 350–1100 nm in the etched AZO films (19.21% for SF6/Ar and 22.07% for CHF3/Ar plasma etched) are found compared to as-deposited AZO films (5.61%). Increment in haze value is due to more scattering of light from the textured surface. These textured substrates are used as front transparent conducting oxide electrode for the fabrication of amorphous silicon solar cells. Solar cells fabricated on etched AZO substrates show 7.76% increase in conversion efficiency compared to as-deposited AZO substrates.

In this paper we present the role of plasma excitation frequency and electsrode separation on the growth of microcrystalline silicon thin films at two different hydrogen dilutions of silane and different power densities. We optimized the process conditions to develop device quality microcrystalline material. Optoelectronic and structural properties of the developed material have been correlated with the solar cell properties. Growth rate ~7 Å/s has been achieved using plasma excitation frequency of 27.12 MHz at 15 mm electrode separation. We have noticed the positive effects after reducing the electrode separation in higher frequency (27.12 MHz). Optimized microcrystalline film of activation energy 0.55 eV and grain size of 14.61 nm has been developed and is applied to fabricate single junction microcrystalline solar cell. Solar cell with initial cell efficiency of 7.75% with short circuit current density of 24.98 mA/cm2 and open circuit voltage of 0.47 V and fill factor of 0.66 has been achieved.

Increasing the efficiency of silicon based Thin Film Solar (TFS) cells, needs use of better light management techniques. A TFS cell developed on nanorods is optically thick for sufficient light absorption, while electrically thin to provide efficient carrier collection. In the present work, ZnO: Al nanorods have been developed on various substrates such as glass, ZnO: Al and Si wafer by hydrothermal method. Light scattering by these nanorods along with the electric field distribution of scattered light has been investigated using FDTD solutions. It has been observed that the scattering efficiency and radiative efficiency exhibits highest values for nanorods on Si wafer among all. (C) 2017 Elsevier Ltd. All rights reserved.

In this paper, we have discussed about the development of high-quality n-μc-SiO:H films by a seeding technique working as a potential back reflector layer (BRL). Highly crystalline and conducting n-μc-Si:H films are used as a seed layer. Phosphorous-doped SiO$_x$:H film with suitable optoelectronics properties has been deposited by a radio frequency plasma enhanced chemical vapor deposition technique using parallel plate reactors (capacititively coupled). Optoelectronics properties have been controlled and optimized varying the deposition parameters such as process pressure, power density, partial pressure of CO2, etc. We have also innovatively replaced the n-layer, i.e., n-a-Si:H in case of the a-Si:H cell and n-μc-Si:H for μc-Si:H cells by this optimized seed + n-μc-SiO:H films. The performance of this n-μc-SiO:H film grown on the n-μc-Si:H seed layer as n-layer as well as BRL of single junction a-Si:H and μc-Si:H solar cells has been evaluated and better Photovoltaic (PV) characteristics of the solar cell are realized as compared to those of the films developed without any seed layer. a-Si:H solar cells with initial efficiency of 9.38% and μc-Si:H solar cell of 8.50% have been successfully fabricated by using improved doped SiO $_x$:H based BRL replacing conventional n-layer of the single junction cells.