Photovoltaic group at CSIR-NPL is the oldest photovoltaic group in the country and has very rich history in silicon based photovoltaics since last five decades, being first to develop silicon solar cells in the country in around mid 70’s. CSIR-NPL is the first laboratory to demonstrate the complete process, from metallurgical grade silicon to solar grade polysilicon and fabrication of solar cells. Currently, the group is involved in basic and applied research spanning from wafer based silicon photovoltaic technology, thin film to latest concepts such as organic and perovskites, organic/inorganic heterostructures, based solar cells development, testing and measurements. Besides, the group is actively involved in the development of waste management technologies such as recycling of waste solar modules, plastic wastes and other electronic wastes for their societal applications.

The photovoltaic metrology group is involved in basic and applied research spanning from wafer based silicon photovoltaic technology, thin film to latest concepts such as organic and perovskites based photovoltaic devices development, testing and measurements. The group is currently engaged in the following R&D activities with an aim to develop efficient and cost effective photovoltaic materials and devices, to develop protocols for precise and accurate measurements of PV cells and modules as well as generating skilled manpower for supporting Indian PV sector.

• Photovoltaic Metrology: Setting national primary standard for solar cell calibration, secondary cell standard and national centre for photovoltaic module testing
• Validation of solar cell efficiency
• Silicon-based Photovoltaics: Unit process development for addressing optical, electronic and electrical losses
• Thin Film Photovoltaics: Nano-crystalline silicon and perovskites/silicon heterojunction solar cells
• Organic photovoltaic devices
• Perovskites photovoltaic devices
• Materials development of organic and perovskites solar cells
• PV Modules: Performance analysis, energy yield and degradation related investigations specific to Indian climatic conditions
• Training Programmes: Solar photovoltaic systems, fundamentals, design and metrology
• Recycling of end-of-life silicon photovoltaic cells and modules.

Ongoing Projects:
1. National primary standard facility for solar cell calibration; Sponsored by Ministry of New and Renewable Energy (MNRE), Govt. of India.
2. Development of interface layer of perovskite solar cells in view of silicon-perovskite tandem solar cell fabrication, Funded by DST.
3. Recycling of Plastic and its Applications in Road Construction Funded by CSIR (in collaboration of CSIR-CRRI).
4. Bulk preparation of p-type and n-type materials for excitonic solar cells, Funded by DST.
5. Design and development of flexible large area 156×156 mm2 modified perovskite mini modules, Funded by DST.
6. Project on training: Workshop and Training on PV materials, devices and systems sponsored by MNRE.

Projects executed/accomplished (Recent past):
1. Development of Efficient Silicon Photovoltaic Solar Cell (CSIR Network Project under TAPSUN programme) (2012-2017)
2. Novel approaches for Solar Energy Conversion (FlexiSolar) (CSIR Network Project under TAPSUN programme) (2012-2017)
3. R&D on thin film solar cells, Funded by MNRE (2011-2017)
4. Advancing the efficiency and production potential for Excitonic solar cells (APEX) Phase II, (International Network Project, Indo-UK) 04.09.2015 to 28.02.2018
5. Development of New Interfacial Layers for Efficient and Stable Excitonic Solar Cells sponsored by SERI, DST, New Delhi from 06/07/2017 to 05/07/2020.
6. Semiconducting Thiophene Based Electronic Materials for Organic Solar Cells sponsored by SERB, DST, New Delhi 07/10/2015 to 06/10/2018.
7. Development of silicon nanowire arrays for effective light harvesting and efficient solar cells; 2014-2019 under CSIR under Young Scientist awardee research grant.
8. Development of Flexible Perovskite Solar Cells sponsored by CSIR through a CSIR-YSA research grant (2016-2021).

Silicon Photovoltaic

The group is working on setting-up apex level testing and calibration facilities for solar cells at CSIR-NPL, the group is actively involved in basic and applied research on different silicon solar cell concepts spanning from wafer based silicon photovoltaic technology including the advanced structures such as black silicon based cells employing excellent light trapping schemes based on nanostructured silicon surfaces, to latest third generation PV concepts such as organic polymer and silicon heterostructures based PV devices, advanced passivation scheme like ALD-Al2O3 based passivation for Passivated Emitter Rear Contact (PERC) structured solar cells and thin/flexible silicon solar cells (<50 microns). The major focus is to develop efficient and cost effective photovoltaic devices/concepts. In the recent past, the group has got expertise in development of value added unit processes (Reflectance and Recombination losses) for high efficiency solar cells development, Standard BSF cell & Passivated Emitter and Rear Contact (PERC) cell.

• The group has developed and demonstrated Proof of concepts for black Si (both mono- and multi-crystalline) solar cells (>17% black silicon solar cells on156x156 mm2).
• The group has also developed processes for silicon surface passivation on p- and n-Si using atomic layer deposition (ALD) deposited Al2O3 film (realized surface recombination velocity <10 cm/s vis-à-vis best reported 1-5 cm/s) as well as ultra thin silicon oxide layer by economic wet chemical route which can also be used as tunnel layer at the back side of the solar cells for efficient charge collection and hence improved efficiency.
• Highly efficient PEDOT:PSS/Si HSCs is demonstrated via an effective surface micro-engineering of the as-cut, low-cost solar-grade thin Si wafers, an aspect rarely addressed before. The HSCs with photo-conversion efficiency >12.25% have been achieved.

Presently, selected research topics of the group include:

• Establishment of national primary standard facility for solar cell calibration and its dissemination to Indian PV industry, R&D organizations and academia.
• Novel light trapping schemes, surface and bulk passivation, ultra-thin layers and new materials for passivated contacts for silicon solar cells.
• Integration of value added unit processes to develop process technology for efficient solar cell using black Si and PERC concepts.
• Development of organic/silicon heterojunction based efficient hybrid solar cells
• Development of flexible solar cells (thinner wafer, <50 microns) for cost effective silicon PV technology
• Recycling of waste silicon solar modules

Thin Film Solar Cells

Silicon Thin Film Photovoltaic (Si-TFPV) activity of CSIR-National Physical Laboratory is one of major laboratory of India for the development of silicon thin film photovoltaic research since many years. In recent past, the group has developed very high frequency (60 MHz & 27.12 MHz) PECVD process for the high rate deposition of nano-crystalline silicon (nc-Si:H) thin films. In addition to increasing deposition rates, reducing non-uniformity and minimizing initial light induced degradation of nc-Si:H thin film layers was also aimed. The optimized p-i-n layers of nc-Si:H were deposited in separate chambers on glass & TCO coated glass substrates (2.5×2.5 cm2 to 10 x 10 cm2). Using these p-i-n layers single junction solar cells & module were made.

Presently group is developing perovskite/silicon hetero-junction thin film solar cells using vacuum based process.

Simulation work for efficient solar cells
The group also involved in simulation work for the improvement of the efficiency of p-i-n silicon solar cells. The efficiency of hydrogenated amorphous silicon (a-Si:H) p-i-n solar cell strongly depend on p-layer band gap and its thickness. i and n- layer band gap also play a key role in the conversion efficiency. Hence we optimized the p, i and n layer band gaps by computer aided one-dimensional AFORS-HET software. Such an optimized value of these band gaps would further helps to prepare efficient solar cells experimentally. In addition, we have used various types of diamond like carbon films as window layer to see its effect on the efficiency of the cells and compared the results with conventional silicon carbon alloy. We are also trying to simulate the layers for Micromorph silicon tandem junction solar cells using ZnO as interlayer between amorphous & microcrystalline silicon solar cells. In addition, simulation approach was also used for HIT and perovskite/silicon hetero-junction solar cells to achieve ~27% and 29 % efficiency respectively, using the same AFORS-HET software.

Plasma Diagnosis
The group is also involved in Plasma Diagnosis of species in different deposition conditions (feed gases, power, pressure operating frequencies, etc) by various diagnostic techniques like, plasma impedance analysis and optical emission. The Plasma diagnostic techniques help for precise optimization of process parameters for deposition of amorphous & micro/nanocrystalline silicon, perovskite etc. materials properties to desired specifications.

Diamond like carbon (DLC) thin films for solar cells application

The group has capability to deposit variety of DLC films such as metal DLC, nano structured carbon, nanocomposite carbon etc. on variety of substrates. Electrical, optical and mechanical properties of diamond-like carbon (DLC, a-C:H) and modified DLC (nitrogen incorporated DLC, a-C:N:H) thin films deposited using radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD) have been explored. a-C:N:H/Si and a-C:H/Si hetrojunction diodes (rectifying circuits), metal (Ti and Cu)/Si/a-C:H based multijunction devices etc. have also been explored. The possible application of DLC and modified DLC films as window layer for amorphous silicon (a-Si:H) based p-i-n solar cell has also been explored using theoretical simulation.
In addition, efforts have also been made to prepare DLC and modified DLC based hard and super-hard (above 40 GPa) coatings. The super-hard and hard coatings realized by employing combination of various layers such as titanium/DLC bilayer and multilayer structure, nitrogenated DLC, oxygen modified DLC, copper/DLC bilayer structure and copper incorporated DLC films. The DLC deposition followed by oxygen plasma treatment was performed for the improvement of the properties of DLC coating deposited on large area (size ~15 cm x 13 cm) glass substrates.

Organic Solar Cells

In the last decades, organic solar cells have been considered a promising photovoltaic technology with the potential to provide reasonable power conversion efficiencies combined with low cost and easy processability. We are working on photovoltaic materials and devices to achieve higher performance and reliability at a lower cost and enhance understanding of the chemistry behind the material growth and the physics behind the device operation. R&D efforts in organic solar cells are focused on developing high efficiency and stable devices with both conventional and inverted solar cell configurations based on donor: acceptor BHJ concept using the soluble polymers/small molecules (electron donors) and modified fullerenes (electron acceptor) in combination with suitable interface layers. The group at CSIR-NPL is very active, vibrant, and is carrying out R&D work by way of addressing the fundamental and applied facets of organic materials and devices. We also aim to understand the stability and degradation processes in solar cells.

The R&D activities in our group concentrate on the development of organic bulk heterojunction solar cells based on (i) existing internationally available donor :acceptor materials, (ii) modifying suitably these existing materials, (iii) developing new donor :acceptor materials, (iv) hybrid polymer inorganic nano-structure, quantum dots and small molecule semiconductors, etc. It also undertakes (v) studies on hole transport layer (HTL), electron transport layer (ETL), photovoltaics, nanoscale characterization, Impedance spectroscopy and optimization of the buffer layer, etc. for the development of the efficient, stable solar cell. Other R&D activities are solution routes for the synthesis of various metal oxides as buffer layers, in situ synthesis of semiconductor nanoparticles in polymer matrix to modify the active layer for solar cells, and nanocrystalline semiconductors by colloidal route. Group working on the design and synthesis of donor and acceptor materials for the organic solar cell to improve the PCE and lifetime of the devices. Major activities in this are: a) Synthesis and characterizations of donor-acceptor polymers and small molecules; b) Synthesis of fullerene-based new acceptor molecules; c) electrochemistry.

Perovskite Solar Cells

Few years ago a new type of solar cell technology was discovered which incorporates perovskite semiconductors as light absorbers and is known as perovskite solar cells (PSCs). PSCs have outperformed all other emerging solar cell technologies and have shown unprecedented improvement in their efficiency from 3.8% to over 25% just within a decade. PSCs are considered to be the most cost effective solar cell technology known so far therefore intense efforts are being made globally to make them commercially viable as soon as possible. PSCs are mechanically flexible and can be made roll to roll via conventional printing techniques. In view of the importance of PSCs for future energy generation, CSIR-NPL has undertaken to develop roll to roll printable flexible perovskite solar cells (FPSCs) and make them commercially viable. We are developing FPSCs both in small area (< 5×5 cm2) as well as in larger area (> 5×5 cm2) via spin coating and printing techniques. We are well equipped with all the necessary tools required for fabrication and characterization of small area FPSCs. The FPSCs are being prepared on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates. The small area FPSCs prepared by spin coating method have shown over 13% power conversion efficiency (PCE) in ~0.1 cm2 area, whereas FPSCs solar modules prepared in 25 cm2 area have shown PCE over 5.5%. The images below show the photographs of small area FPSCs and FPSCs solar module along with their I-V characteristics.

We have also initiated the development of printable FPSCs at CSIR-NPL and for that purpose we have developed in-house a printer to print the PSCs on flexible PET substrates. This printer can print solar cells in A4 size. The image below shows the photograph of ~ 13 cm x 15 cm PET substrate, printed with multiple layers used in PSCs. Successful fabrication of efficient printed PSCs in A4 size will be followed by their roll to roll fabrication. We are in process of setting up a roll to roll solar cell printing facility at CSIR-NPL to develop roll to roll printed PSCs. Along with large area fabrication of efficient FPSCs, we are also doing intense research to understand their degradation mechanisms. The solar cells are being stored in different environmental conditions and stresses and studied for their degradation behaviours with time. A detailed understanding of their degradation mechanisms will enable us to prevent their degradation processes and make them more robust and quite stable in any operational condition.

Recycling and Waste Management

Recycling of waste silicon solar modules

Recently work has also been initiated on recycling of silicon solar cell modules. The method for recovering valuable constituent materials from silicon modules is being carried out by collecting the metal frame, separating the cover glass; removing tadler sheet, removing the EVA from the surface of cell by chemical & thermal treatments etc. Various materials from silicon solar modules were extracted such as silicon wafer, Ethylene-Vinyl Acetate (EVA), metals, glass etc. These materials were extracted using combination of mechanical, chemical and thermal treatments. 

Waste Plastic into Tiles for fabricating structures for Societal Usage

CSIR-NPL has developed a novel technology to utilize waste plastic scrap for designing materials for utilization of tiles in the building of structures and rooms for the general public for societal benefits. The main feature of the CSIR-NPL technology is to utilize waste plastic scrap for designing tiles in the building of structures and rooms for the general public for societal benefits. The various concerns with tiles such as mechanical strength, flame retardancy, water permeability, and UV- protection from sunlight, acid and alkali resistance and antistatic response are successfully addressed by uniqueness in the technology. Recycling of waste plastics are from polyethene bags, bottles, and other containers in the form of a tile, so that these tiles can be inserted in the panels (Fig.). The various challenges like mechanical strength, flame retardancy, water permeability and UV- protection from sunlight and antistatic response is the novelty of the concept. The technology has intellectual property, Indian patent 201611025127 to safeguard the interest of the technology partners. This technology has been transferred to several startups and private industries across India. This technology has also been selected among top Smart Fifty innovations by DST and IIMC. The innovative utilization of waste plastic scrap and fillers for designing of floor, interlock, paver and roof tiles in building of structures and rooms for general public for societal usage. The innovation has been licensed to 7 industries for commercialization.

The group is well equipped with several state-of-the-art facilities for silicon, thin film, organic, perovskite based solar cells & materials and its characterization. Few of those are listed below:
A. Silicon Solar Cell processing

• Diffusion/oxidation/PECVD furnaces, Tempress Systems (2 sets of 2-stack tubes for 6” wafers
• ALD, PICOSUN, Thermal and plasma assisted ALD
• Mask-aligner (EVG)

RTP (AnnealSys, AS-One 150, France)

B. Test & Measurement of PV devices

• I-V measurement system with Class AAA Sun Simulator (21×21 cm2, AM1.0 & AM1.5 solar spectrum) (Newport/Oriel).
• SR and I-V tester (CEP-25HS-50SR Japan) (5×5 cm2)
• Non-contact Minority carrier Lifetime measurements (-PCD, SPV, LBIC) (Semilab, WT 2000 PV)
• Sinton’s Lifetime tester and Sun Voc measurement set up
• Four Point Probe (Quad Pro, Lucas USA)
• UV-Vis-NIR spectrophotometer (Lambda 1050; Perkin Elmer)
• ECV Profiler (WEP, France)
  

C. Thin Film PV Facilities
The group has several deposition systems and in-house characterization facilities. Multi-chamber plasma enhanced chemical vapour deposition (PECVD) system for deposition of amorphous & micro/nano-crystalline silicon films, sputtering & thermal evaporation systems for deposition of metallic & other layers for solar cells. The group has characterization facilities such as IV-CV, temperature dependent dark & photo conductivities, stylus based thickness profilometer, stress measurement setup, etc.

Multi-chamber PECVD system for amorphous & micro/nano-crystalline silicon film growth

Sputtering and thermal evaporation systems for metal deposition

Vacuum based system for Perovskite Growth

IV / CV characterization set up and thickness profilometer

Stress measurement system and Nanoindentation for hardness measurement

D. Organic and perovskite solar cells characterization and device farbrication

• Glove box integrated with the thermal evaporator for device fabrication
• Laser Scrubbing system
• Thermal evaporator system
• Solar simulator
• UV-Vis-NIR spectrometer
• FT-IR spectrometer
• Photoluminescence set-up
• Spin coater
• Electrochemical work station
• Impedance spectrometer

Glove boxes integrated with thermal evaporators

Laser scrubbing system and UV-Vis-NIR spectrometer

1. “ZrO2 layers for anti-reflection and passivation of silicon surface” P. Prathap, Kalpana, Vandana, S.K. Srivastava, C.M.S. Rauthan and P.K. Singh. European Patent No. EP 3381058 B1; US Paten No. 10811546 B2.
2. “Cost effective and Eco-friendly Process for the synthesis of [6,6]-phenyl-C61-butyric acid pentyl ester (PC61BP) under aerobic conditions Inventors”: Rachana Kumar, SamyaNaqvi, Neha Gupta, Suresh Chand US Patent US20160237018 A1, Application number US 15/047,342, Publication date Aug 18, 2016, Filing date Feb 18, 2016.
3. “A process for electrochemical deposition of PEDOT as HTL useful in organic solar cells Inventors:” Asit Patra, Rachana Kumar, V. Agrawal, R. Bhargav, Shahjad, D. Bhardwaj, R. K. Singh, S. Chand, Patent Application No. 201611027796, Application filing date : 23/02/2016, Publication date : 23/02/2018.
4. “Process to deposit diamond like carbon as protective coating on inner surface of a shaped object” Inventor: Sushil Kumar, P.N. Dixit and C.M.S. Rauthan. European Patent No. # EP 2398933 B1, Granted on Aug. 07, 2013.
5. “Process for the preparation of photoluminescent nanostructured silicon thin films using radio frequency plasma discharge” Inventor: Sushil Kumar, P.N. Dixit and C.M.S. Rauthan. US Patent No. # US 8586151 B2, Granted on Nov. 19, 2013.
6. “A process for the preparation of photo luminescent nanostructured silicon thin films” Inventor: Sushil Kumar, P.N. Dixit and C.M.S. Rauthan. Taiwan Patent No. # TW I450320 B Granted on Aug. 21, 2014.
7. “Apparatus for the deposition of diamondlike carbon as protective coating on an inner surface of a shaped object” Inventor: Sushil Kumar, P.N. Dixit and C.M.S. Rauthan. European Patent No. # EP 2589680 B1, Granted on Dec. 24, 2014.
8. “Process to deposit diamond like carbon as protective coating on inner surface of a shaped object” Inventor: Sushil Kumar, P.N. Dixit and C.M.S. Rauthan. Japan Patent No. # 5795266, Granted on 21 August 2015.
9. “An Process to deposit diamond like carbon as protective coating on inner surface of a shaped object” Inventor: Sushil Kumar, P.N. Dixit and C.M.S. Rauthan, Indian Patent No. # 270971, Granted on 28 Jan. 2016.
10. “Process to deposit Diamond like carbon as surface of a shaped object” Inventor: by Sushil Kumar, P.N. Dixit and C.M.S. Rauthan, US Patent No. # US 9260781 B2, Granted on Feb. 16, 2016.
11. “Process to Deposit Diamond Like Carbon as Protective Coating on Inner Surface of a Shaped Object” Inventor: Sushil Kumar, P.N. Dixit and C.M.S. Rauthan, Korean Patent No. # 10-1660557, Granted on 21 September 2016.
12. “Ionic-asymmetric aliphatic diamine terminated rylene dicarboximide organic electronic materials, Inventors”: Rachana Kumar, Samya Naqvi, Mehak Ahuja, Komal Bhardwaj, Rajiv Kumar Singh, Asit Patra, Sushil Kumar Status: Filing under process (2021).
13. “A scalable and environment friendly process for the recycling of pharmaceutical blister packaging for recovery of metallic & polymeric fractions and their exploitation for technological application” Inventors: Parveen Saini, Anuj, Neha, and Sushil Kumar, Status: Filling under Process (2021).

1. Technology Transfer of process know how for the production of Poly(3,4-ethylenedioxythiophene) poly styrene sulphonate (PEDOT:PSS) as HTL for Organic Solar Cells to M/s Sreeni Labs Pvt. Ltd., Hyderabad, India.
2. TECHNOLOGY LICENCED of Low-cost and maintenance-free thermoelectric refrigerator to M/s JTC, New Delhi in May, 2017 (FTT)
3. Development of Low Cost Peltier Based Refrigerator for medicine storage (2 to 7oC) NDA signed M/s REIL Jaipur, Testing and Evaluation (FTT)
4. Process for development of standard polystyrene films, 6th October, 2020 M.s Sirim Scientific Solutions.

Infrared (IR) Indian Certified Reference Standard for calibration of FT-IR instruments with has been developed by CSIR-NPL, a major source of revenue generation.

Dr. Sushil Kumar
Head, Chief Scientist
E-Mail: skumar@nplindia.org
Phone: +91-11-4560 8650

Scientists:

• Dr. Parveen Saini
  Sr. Principal Scientist
  Email: pksaini@nplindia.org
  Phone: +91-11-4560 9505
  
  
• Dr. Asit Patra
  Sr. Principal Scientist
  Email: apatra@nplindia.org
  Phone: +91-11-4560 8360
  
  
• Dr. Sanjay Kumar Srivastava
  Sr. Principal Scientist
  Email: srivassk@nplindia.org
  Phone: +91-11-4560 8617
  
  
• Dr. Rajiv Kumar Singh
  Principal Scientist
  Email: rajivsingh@nplindia.org
  Phone: +91-11-4560 8614
  
  
• Dr. Pankaj Kumar
  Principal Scientist
  Email: pankaj@nplindia.org
  Phone: +91-11-4560 8635
  
  
• Dr. P. Prathap
  Principal Scientist
  Email: prathap@nplindia.org
  Phone: +91-11-4560 8314
  
  
• Dr. Jai Prakash Tiwari
  Principal Scientist
  Email: tiwarijp@nplindia.org
  Phone: +91-11-4560 8640
  

Technical Support:

• Ms. Subha Laxmi
  Senior Technical Officer-II
  
  
• Dr. Neeraj Chaudhary
  Technical Officer-I
  
  
• Ms. Kalpana Lodhi
  Technical Officer
  
  
• Mr. Hawa Singh
  Senior Technician