Chetan Singh Solanki

Performance degradation in field-aged crystalline silicon PV modules in different indian climatic conditions

A survey of field-aged crystalline silicon modules in various climatic conditions in India was carried out, focusing on modules, which show visible signs of degradation. Analysis of the survey data indicates that the power degradation rate is highest in the Hot & Dry climatic zone, followed by the Hot & Humid zone, while it is least in the Cold zone. The degradation in power output of crystalline silicon modules is primarily due to reduction in the short-circuit current, followed by decrease in fill factor while the decrease in open-circuit voltage is very small. Analysis of the survey data also indicates that degradation rate of multi-crystalline silicon is slightly higher than that of mono crystalline silicon.

Synthesis of si nanoparticles from freestanding porous silicon (ps) film using ultrasonication

Porous Silicon (PS) is one of the established materials and can be used in variety of applications in its different forms. Use of monolayer PS film for synthesis of Si QDs is reported here. Nanometer-sized silicon particles are produced by ultrasonic dispersion of thin films in DI water. PS films are characterized using cross sectional scanning electron microscopy and gravimetric analysis while the Si nanopowder is characterized by Raman spectroscopy, Photoluminescence (PL), UV-visible spectroscopy (UV-vis) and FTIR spectroscopy. Sonication for hours causes breaking and oxidation in the film. This reflects as frequency downshift in Raman spectroscopy. Raman peak are resolved into two peaks to study shell type structure of Si nanopowder synthesized. PL exhibits overall red peak shift. Decreasing Tauc bandgap and sharp absorption edge in UV-vis spectra confirms the presence of oxygenated Si nanoparticles in the material tested, confirmed by FTIR. Analysis of all spectra is explained in terms of shell structured Si nanoparticles with Quantum Confinement Luminescent Centre (QCLC) model.

Perspectives for a-Si/c-Si heterojunction solar cells with p or n type base

In this paper, an overview is presented of amorphous silicon-crystalline silicon heterojunction solar cells on different base materials. We also tried to make a comparison with the classically used thermal diffusion. Cells were made with efficiencies of 15.8% and open circuit voltages up to 620 mV on p-type 1 /spl Omega/cm Fz material without the use of high efficiency features. When switching to 0.5 /spl Omega/cm p-type Fz material V/sub oc/ values increased up to 650 mV with a maximum efficiency of 16.4%. To be able to compare the p or n type base for the heterojunction approach, we also investigated the heterojunction emitter on n type Cz material with a thermally in-diffused phosphorus BSF. The highest efficiency achieved so far on this n-type material was 14.1% with a maximum V/sub oc/ of 630 mV. Despite the known shortcomings of p-type base hetero-junction solar cells compared to n-type base hetero-junction solar cells, they might find application in thin film solar cells. First result on thin freestanding films yielded efficiencies up to 9.6%. Using the heterojunction emitter instead of the diffused emitter higher V/sub oc/ were obtained on several investigated materials.

Novel PV module cleaning system using ambient moisture and self-cleaning coating

Soiling is a major concern for PV modules installed in field with power losses ranging from 15% to 65%. In current work, we propose an improved design for a PV module cleaning system based on absorption of ambient moisture and making the module glass super-hydrophilic by TiO2 coating. Initial studies indicate uniform and continuous fibers of diameter of approximately 250nm deposited throughout the sample. A complete prototype design with an automated water delivery system is implemented.

Linking performance of PV systems in India with socio-economic aspects of installation

A survey of PV modules in the field for more than 5 years in India has been conducted The analysis revealed that module degradation rates are linked with the social and behavioral issues of the end users. The appropriateness in system installation, maintenance and hence the degradation depends on the type of ownership of the system, the financial model for the installation and the end purpose. We found that whenever there are cash flows associated with the installations in terms of savings or income generation, the maintenance activities are properly done, irrespective of the type of ownership of the system. Community owned PV installations were found to be better installed and maintained than individual systems because of the presence of institutionalized mechanisms for operation and maintenance.

Optical bandgap tuning of ICPCVD-made silicon nanocrystals for next generation photovoltaics

Superior optical properties of Si-Nanocrystals (Si-NCs) compared to bulk Si, particularly tunability of bandgap by controlling size, can be exploited for realizing next generation “all-Si” tandem solar cells [1]. In this study, we present optical bandgap tunability of Si-NCs made by Inductively Coupled Plasma Enhanced Chemical Vapor Deposition (ICPCVD) using SiO2/SiOx superlattice approach [2]. Deposition time of SiOx sublayer, and hence the related thickness (TSRO), was used as a variable parameter to realize Si-NCs of varying sizes. All multilayer (ML) samples were subsequently furnace annealed at 900°C, to allow for Si-NC formation. Formation of Si-NCs was confirmed by Raman spectroscopy. Transmittance, reflectance and absorptance spectra indicated gradual increase of bandgap with decreasing TSRO. Optical bandgap, ETauc, estimated using Tauc analysis showed an increase in optical bandgap from 1.45 eV to 2.5 eV, as TSRO was varied from 10 nm to 2 nm respectively.

All India Survey of Photovoltaic Module Degradation 2014: Survey methodology and statistics

This paper presents an overview of the 2nd All India Survey of Photovoltaic Module Degradation, conducted in the months of September to December 2014. A total of 1080 modules belonging to different photovoltaic technologies were inspected from 45 different sites which are spread across the 5 different climatic zones of India. This is the first survey in India in which electroluminescence, illuminated and dark I-V measurements, insulation resistance and various other tests were carried out on PV modules installed in the field. The goal of the survey is to determine the degradation in the field-aged PV modules and find correlations between visual, electrical and physical degradation of the PV modules. The purpose of this paper is to present an overview of the survey methodology and statistics to the PV community.

Mechanism for formation of ultra thin SiNx on a-Si - XPS and FTIR studies

The mechanism of the formation of in-situ ultra thin silicon nitride (SiNx) layer (<; 2 nm) on amorphous silicon (a-Si) layer has been studied by Fourier transform infra-red spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The ultra-thin SiNx layers have been obtained through a hot-wire chemical vapor deposition (HWCVD) route. Approximately 1-4 nm thick films of SiNx were obtained on 12 nm and 40 nm thick a-Si at nitriding temperatures of 250 °C and 850 °C. FTIR of the ultra-thin SiNx layer reveals the radicals of decomposed (NH3) gas reacts with a-Si to form SiNx. Further, our XPS results corroborate this mechanism for the formation of SiNx and confirms the formation of ultra thin SiNx layers. This work will enable the development of Si quantum well (Si-QW) superlattice and Si quantum dot (Si-QD) superlattice structures based on a-Si for third generation (3G) solar photovoltaics.

Analyzing impact of background plating from alkaline Ni bath for Ni-Cu metallization

Ni-Cu based front contacts for c-Si cells are plated on patterned SiNx and there could be undesirable background plating leading to shading and shunting losses. In this work, background plating from an alkaline Ni bath is analyzed by Suns-Voc and CoreScan studies. It has been observed that for plating interval of two minutes, pseudo fill-factor show variations till 67% and average Rsh value was less than half of unprocessed cells. Decrease in Rsh for plating interval of one minute was not as severe as for two minute plating.

Junction depth estimation using wet chemical etching for deep junction fabricated by laser doping

In this work, a wet chemical etching technique has been used to estimate the depth of a p-n junction. The wet chemical etchant used is HF/HNO3/H2O solution. Subsequent to this process, optical and electron microscope imaging of cross-section was done to estimate the junction depth. This technique has been used for characterizing deep junction (up to 10 μm) formed by laser doping. Sheet resistances were measured after laser doping on 10 mm × 10 mm area with different scan speed from a heavily doped emitter. Sheet resistance reduces as scan speed is reduced. This indicates formation of deeper junction with lower scan speed. Selective emitter was prepared for chemical etching. Chemical etching leads to staining of n-type surface. An etching of 5 min reveals junction depths of different values from 1.8-8.1 μm. The emitter fabricated by thermal diffusion as source for laser doping was measured to be 419 nm thick. SEM study shows clear difference between n and p-type region. Hence, this technique may be very useful when formation of a deep junction is expected or when SIMS study is very difficult.