Emergence of Photovoltaic Technology
Photovoltaic (photo+voltaic, PV) deals with converting light energy into voltage to generate renewable and environmentally clean energy. In general terms, photovoltaic technology is referred to as solar cell technology, with the sun being the most abundant source of light. It involves the development of photovoltaic materials, photovoltaic devices, device fabrication techniques, and associated technology for maximum sunlight harvesting.
Photovoltaic technology is based on the absorption of light by the photovoltaic semiconductor material that leads to the excitation of electrons through the phenomena called the photoelectric effect, first noted by a French physicist, Edmund Becquerel, in 1839 and later on explained by Albert Einstein in 1905. However, in photovoltaics, the excited electrons are captured into an electrical circuit, and electrical energy is generated. The effect is called the photovoltaic effect. The first photovoltaic module was built by Bell Laboratories in 1954. Since then, the technology has kept on evolving and now has been employed on a large scale.
Requirement of Photovoltaic Technology
Photovoltaic cells, also called solar cells, basically require a photovoltaic material for the conversion of solar energy into electrical energy. Several photovoltaic cells are arranged in series or parallel in an electrical grid to form a photovoltaic system. The photovoltaic materials are n-type or p-type semiconductor materials forming p–n junctions, which absorb the light that generates and moves free electrons in them. The semiconductor layers are sandwiched between front and back conductive layers connected to an electrical circuit in which the electron moves and an antireflection coating at the top in order to ensure maximum sunlight absorption. It is essential to have efficient semiconductor material for maximum electricity generation and proper arrangement of different layers of material to effectively capture the electrons for their movement into an electrical circuit, thereby generating electricity. Further, protective layers are added to protect the cells from various environmental factors and to maintain a longer shelf life. Hence, efficient PV materials, efficient design of solar cell modules, and cost-effective fabrication and associated techniques are required to make it an economical and readily available technology.
Demand for Solar Energy
The renewable and pollution-free nature of solar energy and the high availability of sunlight in several countries make photovoltaic technology an ideal alternative for depleting fossil fuels to meet present and future energy demands.
India is a fast-developing solar industry with a solar installed capacity of 66.97 GWAC as of the year 2022 and ranks fourth globally in 2021 in solar power generation. India has a solar potential of about 748 GW, assuming 3% of the wasteland area will be covered by solar PV modules.
According to the WIPO Intellectual Property Statistical Country Profile 2021, 122 Indian PCT publications in 2019-2021 related to renewable energy. Undoubtedly, the energy demand is going to increase further with population growth. Therefore, it is necessary to invest in photovoltaic technologies and promote innovation in the field to make the technology commercially available and economically viable. Promoting the patenting of new innovative technology is a critical step in keeping the inventors motivated.
With its present solar manufacturing facility, India has managed to produce solar PV cells with a capacity of around 3 GW/year and solar PV modules with a capacity of around 10 GW/year. However, India does not have a manufacturing facility for Polysilicon/Wafer/Ingots solar cells, but India has already started an initiative to invite tenders to establish different solar PV manufacturing facilities through transparent, competitive bidding. Also, the Government of India have launched various schemes to encourage the generation of solar power in the country, like Solar Park Schemes, VGF Schemes, CPSU Schemes, Defense Scheme, Canal bank & Canal top Scheme, Bundling Scheme, Grid Connected Solar Rooftop Scheme and others in order to invite investor, stakeholder and intellectual property rights (IPR) holder to explore Indian photovoltaic market [Ministry of New and Renewable Energy, GOI].
Shockley–Queisser Limit
The Shockley–Queisser limit, which is theoretically the maximum solar-to-electrical conversion efficiency in an ideal solar cell, is 33.7 % if all the power is contained in sunlight (about 1000 W/m2) under AM 1.5. The maximum solar conversion efficiency achieved is 33.16% for a single-junction solar cell with a bandgap of 1.34 eV. For silicon solar cells, the maximum solar conversion efficiency is 32 % due to its unfavourable band gap of 1.1 eV, which causes the photon energy in excess of the semiconductor’s bandgap to be wasted as heat. The main target of the innovations is to achieve maximum solar efficiency through the inventions of new photovoltaic materials and associated PV technology.
Generations of Photovoltaic Technologies and Their Limitations
Photovoltaic technology has developed through various generations by exploring different possibilities. The first generation of photovoltaic technology mainly comprised silicon wafer solar cells in which single-crystal semiconductor is grown epitaxially, layer-by-layer on a monolithic wafer. The first-generation photovoltaic solar cells also include monocrystalline, polycrystalline, and GaAs solar cells. Although silicon solar cells show great efficiency and silicon is also incredibly abundant, there are several disadvantages associated with single-wafer solar cells. Most important are the bulky nature of the silicon solar cell and the cost associated with the development and fabrication of solar devices with single crystalline silicon.
The second generation of solar cells was based on thin film deposits of semiconductors. Different types of semiconductor materials such as amorphous silicon, polycrystalline silicon, microcrystalline silicon, cadmium telluride, copper Indium selenide and sulphide were used for thin film solar cells. Apart from that, various inexpensive thin film deposition technologies were developed in order to reduce the cost of fabrication of thin film solar cells. The advantage of thin-film solar cell technology is that thin-film layers can be produced separately and then integrated using bonding, lamination, and other similar methods; it is also less expensive.
Alternatively, in some cases, the entire structure may be sequentially grown without the need for any mechanical integration of the individual layers. This flexibility in a manufacturing method makes it possible to implement new design approaches in producing a better photovoltaic device. Lightweight solar cells could be developed through thin film technology, but with this technology, the efficiency of single crystalline silicon solar cells could not be achieved.
The third generation of photovoltaic technology does not rely on traditional PN junctions to separate photo-generated charge carriers, whereas the new devices include photoelectrochemical cells (dye-sensitized solar cells), polymer solar cells, perovskite solar cells, nanocrystalline and quantum dot solar cells.
The considerable advantages of third-generation photovoltaic solar cells may include solution-processable technologies, efficient technologies for commercial production, mechanical toughness, and high efficiencies at higher temperatures. Also, multi-junction devices got more attraction in general for being more efficient in converting solar energy into electricity than regular PV devices. However, the development of these devices is currently hindered by the complexity of creating multi-junctions of suitable semiconductors, their manufacturing processes, and their high cost.
Sometimes, the photovoltaic technology involving graphene as absorber material in direct, functionalized, doped, and composite form is termed the fourth generation of photovoltaics.
Present Scenario and Plausible Future Advancements
Analyzing the research and innovation published in research articles and patents worldwide provides an idea about the progress made in photovoltaic technology. The expiry of critical patents also opens new windows of opportunity for countries and their innovators to catch up with the latest technology. Here, we have analyzed several advancements in photovoltaic technology that have been registered through patents and may open new dimensions in photovoltaics.
Figure 1 shows the trend with respect to PCT publication since 2002, demonstrating the growth of renewable energy technology relating to solar energy, fuel cells, wind energy, and geothermal energy. The number of published PCT applications relating to solar energy increased by 678 per cent over the past 17 years. The numbers are much higher than any other renewable energy patent, showing that solar has been the leading technology every year since 2009 [WIPO, 2019].
Figure 1. Trend with respect to PCT publication relating to renewable technology since 2002.
An article by Mahmood H. Shubbak in 2019 shows that 39% of the global patents belong to solar cell technologies. The solar panels group forms the second largest group with a share of 27%, followed by testing techniques (21%) and electronics (6%). Geographically, 95% of photovoltaic patents were filed by inventors in the USA, Japan, Korea, China, Germany, Taiwan, and France. Despite the higher number of patent applications filed by East Asian countries, the international business potential of their patents is still far behind that of their Western counterparts.
The most influential PV Patent applications based on their patent impact factor and citation are given in descending order. Data extracted from PATSTAT 2016b [M.H. Shubbak, Renewable and Sustainable Energy Reviews 115 (2019) 109383].
Table 1. The most influential PV patent applications
| Patent Number | Year | Citations | Patent impact factor | Country | Scope |
| JP19930294633 | 1993 | 688 | 29.9 | Japan | c-Si Cell |
| US20010975572 | 2001 | 366 | 24.4 | USA | PV Panels |
| US19930173294 | 1993 | 492 | 21.4 | USA | Monitoring |
| US20000527316 | 2000 | 253 | 15.8 | USA | Thin-film Cells |
| US20010878523 | 2001 | 236 | 15.7 | USA | Organic Cells |
| US19990454063 | 1999 | 222 | 13.1 | USA | Multi-junction Cells |
| US20020217861 | 2002 | 181 | 12.9 | USA | Optical/Thermal |
| US19920894879 | 1992 | 293 | 12.2 | USA | Energy Storage |
| US20020067357 | 2002 | 125 | 8.9 | USA | Taiwan Lighting Devices |
| DE20091018126 | 2009 | 61 | 8.7 | Germany | PV Electronics |
Considering the latest development in the field of photovoltaics, Solarwindow Technologies Inc. in US9772260B2 recently disclosed integrated photovoltaic devices as smart sensors for intelligent building energy management systems. The output parameters from the device are used to provide information about light intensity and ambient temperature, in addition to providing power to an intelligent building energy management system. This kind of technology could help create automatic photovoltaic systems that could operate and optimize according to external parameters.
Typically, a photovoltaic device with multiple semiconductor layers of different bandgaps is 50-56 % more efficient. However, the current-matching procedure complicates the design and decreases the conversion efficiency of the device. Sunlight Aerospace Inc. in US9087948B1 reports the manufacturing method of multi-junction PV modules having photovoltaic devices that include a plurality of junction layers with different absorber materials having different bandgaps arranged in a stack on top of each other, produced from photovoltaic layer-based on CIGS alloys, CdTe alloys and Si alloys. This invention provides thin-film technology as an alternative means of making a multi-junction photovoltaic device with expanded capabilities and application range.
In patent application US9171991B2, Dow Global Technologies LLC disclosed a highly automated method of interconnecting flexible solar cells to form solar modules with a wide variety of sizes and electrical characteristics. The process is fast and economical, providing many attributes of a “pseudo monolithic integration” scheme for different types of solar cell materials suitable for use on flexible substrates that have previously been attainable only on rigid substrates.
US-based IntriEnergy, with India patent number 390862, has secured a patent for its technology platform in India. D·ARK anti-reflective coating increases the energy output of any solar cell by 10%; IntrinSiC silicon-carbide captures 40% more of the sun’s spectrum along with quantum energy dots to optimize energy flow. The technology claims to increase the overall energy output of a solar cell by up to 60% and can be applied to any solar cell during the manufacturing process, creating a high-efficiency, low-cost solar cell.
Chinese patent application CN116093191A, filed by Zhejiang Jinko Solar Co Ltd, provides a solar cell and a photovoltaic module that reduces optical loss of a doped conductive layer in TOPcon solar cell technology comprising textured silicon substrate while reducing lateral transmission loss of current, thereby improving front cell efficiency and cell bifacial rate. Another patent application, CN115985803A, filed by Guangdong Liansu Banhao New Energy Technology Group Co. Ltd, provides an antireflection film plating unit and a texturing unit to generate textured silicon for a photovoltaic module.
Moreover, in CN115976651A, Jiaxing Xiaochen Photovoltaic Technology Co. Ltd discloses a texturing additive for preparing a large-size Topcon solar cell to reduce cost and improve efficiency laterally. Chinese company Far East Curtain Wall Zhuhai Co ltd with CN218850677U has secured a patent for a thin-film solar cell photovoltaic curtain that can increase the thermal-insulated heat preservation effect of curtain and can reduce one kind of light pollution apart from generating power.
In patent application WO2008045814A2, Solexel, Inc. discloses pyramidal three-dimensional thin-film solar cells arranged in solar module structures and a method for assembling the same. The pyramid-shaped 3-D TFSC significantly reduces the disadvantages and problems associated with previously developed TFSCs, both in terms of efficiency and manufacturing cost and could be used in solar glass applications, building facade applications, rooftop installation applications, as well as for centralized solar electricity generation.
Apart from device design, different patent applications have been filed and acquired for perovskite-based photovoltaic cells. Wuhan University, with patent application CN116017992A, has filed a patent for a narrow-bandgap perovskite photovoltaic cell with a photoelectric conversion efficiency reaching 22.26 per cent and full perovskite laminated cell with a photoelectric conversion efficiency of 26.4 per cent. At the same time, East China Normal University, with CN110783464B, acquired a patent for photovoltaic devices based on organic-inorganic hybrid perovskites.
The University of Chicago, with WO2010008672A1, has patented a novel semiconducting photovoltaic polymer with conjugated units that provide improved solar conversion efficiency that can be used in electro-optical and electric devices.
Conclusion
The continuous growth and trends in photovoltaic technology have clearly demonstrated its potential to be a significant alternative source of energy that could meet increasing energy demands. It is to see which advancements and innovations around photovoltaics will be the game changers to make photovoltaic technology more user-friendly, commercially viable and readily available. A considerable number of patent applications filed in the field of photovoltaics clearly show the interest of technologists in this area of innovation.
Furthermore, India has taken various policy measures, including the declaration of trajectory for Renewable Purchase Obligation (RPO) for solar, structuring guidelines for procurement of solar power through a tariff-based competitive bidding process, standardizing the deployment of solar photovoltaic systems and devices, providing infrastructure for solar projects among others for the development of solar-based smart cities in India. India is currently welcoming various investors and stakeholders to invest in Indian solar projects, as well as encouraging IPR holders to exploit their IP assets in Indian photovoltaic markets, secure more IP rights in India, and benefit from their IP worth.
