National Centre for Photovoltaic Research and Education

Reforms in the electricity sector along with various renewable-energy-promotion policies have increased the importance of small grid-connected photovoltaic (PV) systems utilizing single-stage single-phase inverters. Ruggedness, reliability, and cost effectiveness are the desirable characteristics of such inverters used in distributed low-power applications. Schemes based on one-cycle control (OCC) which do not require the service of a phase-locked loop for interfacing the inverter to the grid are increasingly being employed for such applications. However, the OCC-based schemes reported earlier require sensing of the grid voltage which somewhat offsets one of the inherent strengths of OCC-based systems. In an effort to overcome the aforementioned limitation, an OCC-based grid-connected single-stage PV system is proposed in this paper which does not require to sense the grid voltage. Further, it requires less number of sensors (two) as compared to that required (four) in the earlier reported scheme for the implementation of the core controller comprising of OCC and maximum-power-point-tracking blocks. The viability of the proposed scheme is confirmed by performing simulation and experimental validation.

Graphene-assisted charge transportation doubles the power conversion efficiency of PCPDTBT:PCBM:ZnO-based bulk heterojunction solar cells.

Highly oriented and homogeneously distributed single crystalline zinc oxide nanowires (NWs) are fabricated on amorphous glass substrates using soft solution growth approach. The nanowire films and sol-gel grown ZnO films are devised and tested for UV light detection applying four-probe conductivity measurements. As-grown ZnO NWs film device demonstrates three orders enhancement (sensitivity = 440) in conductivity at room temperature under an illumination of 365 nm UV light, while the sol-gel based thick film reveals two orders of enhancement in device conductance. A clear correlation of conductivity and photoluminescence measurements suggest that surface oxygen vacancies (singly charged/Vo+) which render higher green defect luminescence intensity (IG/IUV = 1.8) in ZnO NWs leads to poor dark conductance and higher photo-conductance. Post growth annealing of nanowire arrays either in air (IG/IUV = 0.85) or oxygen ambience (IG/IUV = 0.38) results in reduction of green defects and corresponding suppression of photocurrent. Higher concentration of surface traps also leads to persistent photocurrent due to ionization of oxygen vacancies and creation of perturb host states under UV light excitation.

We experimentally explored vertical mounting of bifacial modules of different bifacialities for mitigating soiling in Mumbai, where the dust accumulation rate in terms of energy loss per day can be as much as 0.45%. Bifaciality is commonly referred to the ratio of the back side value to the front side value of any of the performance parameters I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> , P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> , or η. The energy loss due to soiling in vertically mounted bifacial modules and monofacial and bifacial modules mounted at the latitude angle are compared. The experiments reveal that the vertically mounted bifacial modules have nearly zero soiling loss; bifacial modules mounted at latitude angle with 90% bifaciality have lower soiling rate; the energy yield of vertically mounted bifacial modules with 90% bifaciality can exceed that of bifacial modules mounted at latitude angle after three weeks if the modules are left to soil without cleaning; the peak temperature of operation of vertically mounted bifacial modules is seen to be 15 °C lower than that of bifacial modules mounted at latitude angle, implying potential benefits in long-term reliability and performance ratio; combining vertically mounted bifacial modules and bifacial modules mounted at latitude angle, a nearly flat, extended generation profile can be obtained.

Degradation in electrical performance of photovoltaic (PV) modules is related to the degradation of the solar cells and laminate materials in the modules, which often shows up as hot spots in infrared (IR) thermography. The analysis of the IR data of crystalline silicon modules inspected in the field during the All India Survey of Photovoltaic Module Reliability in 2016 is being presented in this paper, along with its correlation to the electrical degradation in these modules. The thermal mismatch in the PV modules has been quantified in terms of a Thermal Mismatch Index, based on the difference between the highest cell temperature and the representative module temperature. Modules with high thermal mismatch (hot cells) under MPPT condition show high power degradation, caused mainly due to fill factor degradation. Modules with hot cells show higher degradation in “Hot” climatic zones as compared with “Non-Hot” climates. The analysis indicates that modules having cracks and hot cells have higher power degradation than modules having cracks but no hot cells. This indicates that the worst cracks tend to create hot cells in the modules, while the benign cracks (which have lesser impact on power output) do not affect the cell temperature to that extent.

The perfect crystalline nature along with a defect ridden surface controls the electrical and magnetic properties of ZnOnanowires. Herein, a soft chemical approach is presented to grow ZnOnanowires in powder as well as highly oriented nanowirefilm form. Photoluminescencemeasurements reveal high surface defects in as-grown nanowire and post growth annealing treatment in argon and oxygen atmosphere reduces intensity of defect emissions. Magnetic measurements illustrate the ferromagnetic nature of submicron sized zinc oxide (ZnO) nanorods arising due to singly charged oxygen vacancies.Nanowires show diamagnetic behavior when annealed at higher temperature in oxygen while argon annealing does not affect the magnetic behavior. In an analogous manner, we also investigated the effect of surface defects on electrical properties and correlated electrical conductivity with a responsible defect state.

An ITO/FTO free AuNP functionalized ZnO NW photoanode in a dual role such as photo active centers for catalytic activity and an efficient transport medium for photo-generated charge carriers.

Hydrophobic ZnO, C-dots, Z@G and Z@C_dots applied as cost-effective acceptors in non-fullerene-based polymer bulk heterojunction solar cells resulted in significant device performance with a maximum efficiency of 3.9% in direct configuration.

In perovskite solar cells (PSCs), defects and interfacial properties are critical and govern the device's performance. To enhance the performance, effective defect passivation and recombination reduction are crucial. This work reports phenethylammonium iodide (PEAI) treatment of lead-excess perovskite film for low-temperature carbon-based PSCs. The PEAI post-treatment leads to the formation of a crystallized (PEA)2PbI4 2D layer on top of 3D perovskite. Apart from passivating the grain boundaries, the 3D/2D stack improves the interface between perovskite and carbon, reducing the interfacial recombination. Moreover, the passivation reduces the trap state density and provides improved energy alignment with the carbon layer. The reduced defects and non-radiative recombination resulted in performance enhancement from 10.16% to 11.76% with good reproducibility. c-AFM and photoluminescence (PL) imaging have been performed to visualize recombination sites and passivation quality post-PEAI treatment. Furthermore, the voltage-dependent PL imaging of PSCs reveals rapid quenching in the maximum power point regime substantiating efficient charge extraction in passivated devices. The prepared devices show noteworthy stability retaining around 60% of initial performance after 1000 hours.

A new anti-reflection coating based on amorphous barium titanate (a-BTO) was developed using RF magnetron sputtering technique.

Energy loss due to soiling of photovoltaic modules is one of the most reported problems in sunbelt countries. Anti-soiling coatings (ASC) which reduces soiling, offers an economical and universal solution. Since ASC is applied on the outer surface of the PV module, durability of these coatings is essential. In this paper, we compared the field degradation rates of 4 different (named A, B, C and D) commercial hydrophobic ASC in Mumbai, India (warm and humid climate). The degradation rate of ASC was determined in terms of reduction of contact angle per day. Contact angle of one of the ASC changed from hydrophobic to hydrophilic in 5 days of field exposure and all other coatings became hydrophilic in 40 days of field exposure during rainy season. Degradation rates of ASC during rainy season was more than 4 times than that of non-rainy season for all coated samples. Accelerated laboratory tests using acidic water (pH 6) showed good correlation with field exposure for coatings A and C. Laboratory studies on the mechanical impact of rain showed linear rates of degradation for all coated samples, which correlated well with the field exposure study during rainy season. This indicates that the mechanical impact of rain, in addition to the pH and UV exposure reported earlier, as a significant stressor for ASC.

Remotely empowered wireless sensor networks use different energy resources including photovoltaic solar cells, wireless power transmission, and batteries. As another option the electromagnetic energy available in the ambient can be harvested to power these remote sensors. This is particularly valuable if it is desirable to harvest the ambient energy available in the wide range of electromagnetic spectrum. This has motivated the research for developing energy harvesting devices which can absorb this energy and produce a DC voltage. Rectenna, an antenna coupled with a rectifier, is the main component used for absorbing electromagnetic radiation at GHz and THz frequencies. Rectifying MIM tunnel diodes are able to operate at tens and hundreds of GHz frequency. As the preliminary steps towards development of high-frequency rectifiers, this paper presents fabrication and DC characterization of two new MIM diodes, Ti-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>TiO</mml:mtext><mml:mtext>2</mml:mtext></mml:msub></mml:math>-Al and Ti-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>TiO</mml:mtext><mml:mtext>2</mml:mtext></mml:msub></mml:math>-Pt. G-V analysis of the fabricated diodes verifies tunneling. Brinkman-Dynes-Rowell model is used to extract oxide thickness of which the derived value is around 9 nm. Ti-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>TiO</mml:mtext><mml:mtext>2</mml:mtext></mml:msub></mml:math>-Pt diode exhibits rectification ratio of 15 at 0.495 V, which is more than rectification ratio reported in earlier works.

We have carried out a feasibility study on using inductively coupled plasma CVD (ICP-CVD) based SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> :H as an anti-reflective coating and for surface passivation of c-Si solar cells. It is seen that for certain range of gas flows the films showed blistering upon firing. Film deposition process was optimized to eliminate the blistering problem. Using extensive fourier transform infrared spectroscopy (FTIR) studies, it is shown that the blistering is due to release of hydrogen in the film and process optimization should target to achieve low hydrogen concentration. Optimized recipes with low interface state density and high positive charges were developed and surface recombination velocity of 1.9 cm/sec was obtained..

Superior optical properties of Si-nanocrystals (Si-NCs) compared with bulk Si, particularly tunability of bandgap by controlling size, can be exploited for realizing next-generation Si tandem solar cells. In view of this, optical bandgap tunability of Si-NCs fabricated by Inductively Coupled Plasma Enhanced Chemical Vapor Deposition (ICPCVD) is presented. The SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x&lt;;2</sub> /SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superlattice approach was used for realizing Si-NCs with tight size control. Deposition time of SiOx sublayer and, hence, the related thickness (TSRO), was used as a variable parameter to realize Si-NCs of varying sizes. Formation of Si-NCs was verified by transmission electron microscopy and Raman spectroscopy. Using XPS analysis, the stoichiometry parameter x was estimated to be 0.82 for SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> sublayer. The optical bandgap E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Tauc</sub> estimated using Tauc analysis was observed to be tunable from 1.57 to 2.52 eV as the size of Si-NCs was varied from 5.8 (±0.5) to 2 (±0.4) nm, respectively.

This chapter contains sections titled: Introduction Economic Expectations of OPV Device Architecture Operational Principles Experimental procedure for synthesis of hydrophobic nanomaterials Characterization of Synthesized ZnO Nanoparticles and ZnO Decorated Graphene (Z@G) Nanocomposite Hybrid Solar Cell Fabrication and Characterization

Photovoltaic (PV) modules operating under high voltage stresses are known to conduct leakage current through different layers consisting of glass, encapsulant, backsheet, etc. Since this leakage current is responsible for Potential Induced Degradation (PID), correlating the leakage current to material properties is important for predictive models for PID dependence on total charge transferred. In this paper, a 2D Finite Element Method (FEM) based model is developed to simulate the leakage current flowing in a c-Si module with front glass-encapsulant-cell-encapsulant-backsheet configuration which is excited with 1000 V. The environmental factors such as temperature and surface wetness are considered and the leakage current and electric field distributions in the module are obtained. The Arrhenius behavior of the leakage current is studied and the dependence of overall activation energy on electrical properties of module materials is analyzed.

Photovoltaic modules are typically rated at three test conditions: STC, NOCT and Low irradiance. This paper discusses the power rating of modules at twenty-three test conditions as per the IEC 61853-1 standard using a new outdoor test method. Polycrystalline silicon modules from four different manufacturers were installed on the two-axis tracker and monitored for up to 12 continuous days. In order to obtain the I-V data at wide range of temperatures and irradiance levels, four identical modules were simultaneously installed on the tracker with and without thermal insulators on the back of the modules and with and without mesh screens on the front of the modules. This work investigates the minimum number of days required to perform power rating of modules at twenty-three test conditions.

Wet chemical etching is utilized to enhance defect density by introducing surface roughness in ZnO NWs. Morphological investigations using SEM clearly show the surface roughness and the diameter/length decreases due to anisotropic etching of the NWs in 0.5-0.01M acid. Increased defect band intensity in PL measurements for etched samples indicates roughness induces defects at nanowire surface. Dark conductivity of NWs array film decreases after etching, this is due to creation of high depletion layer (higher concentration of surface adsorbed oxygen results in higher surface built- in potential) between NW grains. UV light irradiation results in three order enhanced conductivity for etched NWs array film, while only two order increase in conductivity has been measured in as-grown arrays. The enhancement in photosensitivity for etched nanowire is due to high surface defects created by the surface roughness. Higher surface defect states lead to slow photoresponse and high degree of persistency in photocurrent.

A systematic investigation of POCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> based diffusion optimization for the formation of homogeneous emitters in P type c-Si solar cells is presented. The gas composition, exhaust rates, flat zone temperature profile have been varied to achieve uniform sheet resistance across each wafer and wafers along the boat. A one standard deviation of ~ 5 ohm/square has been achieved on 125 mm × 125 mm mono like wafers from the initial variation of 37 ohm/square. In addition to the sheet resistance, secondary ion mass spectroscopy, ellipsometry, life time and emitter saturation current density measurements are performed for better understanding of the optimization.

Dust deposition on photovoltaic module can reduce energy generation up to 50% if not cleaned for 4 months in Mumbai, India (warm and humid climate). Hydrophobic (contact angle> 90°) anti-soiling coating (ASC) is a cost-effective mitigation strategy to reduce soiling. In this paper, we compared the cleaning efficacy of 4 different commercial hydrophobic anti-soiling coatings (on solar glass and PV modules) with a not-coated sample. All coated glass samples (A, B, C and D) showed higher cleaning efficacy (lower soiling loss) than the not-coated glass sample after cleaning with a 45 μl deionized water droplet. This was also confirmed by field exposure study done on PV modules (for coating B,C and D). Cleaning efficacy of the coating D (on PV module) decreased significantly after 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> manual cleaning run, indicating abrasion caused by the cleaning tool, implying that the selection of cleaning methods/tools is critical. Under controlled environment (on solar glass) cleaning efficacy of all coated glass samples reduced by a factor of 6 (average) as the rolling water droplet travels from top to bottom, covering a total distance of 3.6 cm, This is due to the reduction in speed of the water droplet rolling off the surface as it accumulates more dust. Roll of angle for clean coated glass increases by a factor of 2 (for coating A,C and D) when measured on dust deposited glass substrate, indicating that roll-off angle depends on the surface of the ASC coatings, which may vary with exposure time and environmental conditions like soiling rate. Ranking of cleaning efficacy of ASC under field exposure correlated well with the roll-off angle measured on soiled samples in controlled experiments. This suggest roll - off angle as an important measure for the evaluation of the anti-soiling coatings.