Author links open overlay panelhttps://doi.org/10.1016/j.eng.2022.07.008Get rights and contentUnder a Creative Commons licenseopen accessSolar photovoltaic (PV) technology is indispensable for realizing a global low-carbon energy system and, eventually, carbon neutrality. Benefiting from the technological developments in the PV industry, the levelized cost of electricity (LCOE) of PV energy has been reduced by 85% over the past decade. Today, PV energy is one of the most cost-effective electrical power sources worldwide. For instance, a PV power price of merely 0.0104 USD·(kW·h)−1 was achieved in Saudi Arabia in April 2021.In the coming years, innovative technological developments should help further boost the PV power conversion efficiency (PCE), reduce the PV energy cost, and expand the PV industry. With the ever-increasing proportion of PV in the energy system, the challenges posed by the regional intermittence and randomness of PV energy will manifest and provide opportunities for new technologies, including the integration of PV with other forms of energy and/or various energy storage techniques. We believe that, in the long term, extended PV systems with the active participation of green hydrogen energy are key to the deep decarburization and sustainable development of our society.High PCE and low LCOE, which ensure the competitiveness of PV energy, rely extensively on the development of PV technologies. Wafer-based crystalline silicon (c-Si) solar cells have been the dominant PV technology since the 1960s and are still undergoing considerable progress, with multiple technological breakthroughs in both academia and the industry over the past decade (Fig. 1,,, ).For example, in research, the charge carrier-selective contact—that is, the tunneling oxide passivating contact (TOPCon, also called polycrystalline silicon on oxides (POLO)), initiated by Fraunhofer ISE in 2013, —shows enhanced surface passivation and carrier extraction, compared to the passivated emitter and rear cell (PERC), the foremost c-Si cell in the market. Based on the TOPCon, the PCE of homojunction c-Si cells can reach 26% for front-and-back contact (FBC) cells (▲ in Fig. 1,,, ) and 26.1% for interdigitated back contact (IBC) cells (named POLO-IBC by Institute for Solar Energy Research in Hamelin) (△ in Fig. 1,,, ). In addition, heterojunction technology (HJT), which uses n-type/p-type amorphous silicon (a-Si) as the selective contact and intrinsic (undoped) a-Si as the passivation layer, allows high charge extraction from the c-Si base. By combining HJT with IBC, the HJ IBC cell constructed by Kaneka Corporation (Japan) in 2017 dem. The proportion of PV energy in the overall energy system has been steadily increasing. According to World Energy Transitions Outlook of the International Renewable Energy Agency, PV energy will comprise more than 10% of the energy system by 2030, with a cumulative installed capacity of over 5000 GW (green columns in Fig. 1,,, ). By 2050, PV energy could account for more than 35% of the overall power supply, with a cumulative installed capacity of 14 000 GW. However, this increasing proportion of PV within the power grid is challenged by its regional intermittence. To overcome this, multi-energy complementary systems with PV and other renewable energies (e.g., hydropower and wind power) are being developed. In addition, extended PV systems comprising PV and various energy storage units, including physical (hydropower), electrochemical (battery), and chemical (hydrogen) solutions, are emerging (Fig. 2).Photovoltaic-electrochemical (PV-EC) systems, which utilize PV power for water electrolysis with the generation of green hydrogen, are an effective strategy for storing massive amounts of solar energy, as well as a prospective way of permitting the intensive participation of PV energy in the energy-structure transformation process. This is because the green hydrogen generated by PV technologies could serve as both a significant energy source and an essential. With the rapid development of c-Si-cell-based PV technologies, PV energy is becoming the most cost-effective renewable energy source, leading to the fast growth of PV energy proportion in the global energy system. The future PV market will still be dominated by c-Si cells, while an in-depth understanding of the exact factors contributing to power c.
