Over the past decade, the global cumulative installed photovoltaic (PV) capacity has grown exponentially, reaching 591 GW in 2019. Rapid progress was driven in large part by improvements in solar cell and module efficiencies, reduction in manufacturing costs and the realization of levelized costs of electricity that are now generally less than other energy sources and approaching similar costs with storage included. Given this success, it is a particularly fitting time to assess the state of the photovoltaics field and the technology milestones that must be achieved to maximize future impact and forward momentum. This roadmap outlines the critical areas of development in all of the major PV conversion technologies, advances needed to enable terawatt-scale PV installation, and cross-cutting topics on reliability, characterization, and applications. Each perspective provides a status update, summarizes the limiting immediate and long-term technical challenges and highlights breakthroughs that are needed to address them. In total, this roadmap is intended to guide researchers, funding agencies and industry in identifying the areas of development that will have the most impact on PV technology in the upcoming years.

The U.S. Department of Energy's Office of Scientific and Technical Information

We report gallium arsenide (GaAs) growth rates exceeding 300 µm h⁻¹ using dynamic hydride vapor phase epitaxy. We achieved these rates by maximizing the gallium to gallium monochloride conversion efficiency, and by utilizing a mass-transport-limited growth regime with fast kinetics. We also demonstrate gallium indium phosphide growth at rates exceeding 200 µm h⁻¹ using similar growth conditions. We grew GaAs solar cell devices by incorporating the high growth rate of GaAs and evaluated its material quality at these high rates. Solar cell growth rates ranged from 35 to 309 µm h⁻¹ with open circuit voltages ranging from 1.04 to 1.07 V. The best devices exceeded 25% efficiency under the AM1.5 G solar spectrum. The high open-circuit voltages indicate that high material quality can be maintained at these extremely high growth rates. These results have strong implications toward lowering the deposition cost of III-V materials potentially enabling the deposition of high efficiency devices in mere seconds.

Silicon is the dominant semiconductor in many semiconductor device applications for a variety of reasons, including both performance and cost. III-V materials exhibit improved performance compared to silicon, but currently, they are relegated to applications in high-value or niche markets, due to the absence of a low-cost, high-quality production technique. Here we present an advance in III-V materials synthesis, using a hydride vapor phase epitaxy process that has the potential to lower III-V semiconductor deposition costs, while maintaining the requisite optoelectronic material quality that enables III-V-based technologies to outperform Si. We demonstrate the impacts of this advance by addressing the use of III-Vs in terrestrial photovoltaics, a highly cost-constrained market.

The high cost of high-efficiency III-V photovoltaic devices currently limits them to niche markets. Hydride vapor-phase epitaxy (HVPE) growth of III-V materials recently reemerged as a low-cost, high-throughput alternative to conventional metal- organic vapor-phase epitaxy (MOVPE) growth of high-efficiency solar cells. Previously, we demonstrated unpassivated HVPEgrown GaAs p-n junctions with good quantum efficiency and high open-circuit voltage (V_oc). In this work, we demonstrate the growth of GaInPby HVPE for use as a high-quality surface passivation layer to GaAs solar cells. Solar cells grown with GaInP window layers show significantly improved quantum efficiency compared with unpassivated cells, increasing the short-circuit current (J_SC ) of these low-cost devices. These results show the potential of low-cost HVPE for the growth of high-quality III-V devices.

We report the development of Ga_0.5In_0.5P/GaAs monolithic tandem solar cells grown by dynamic hydride vapor phase epitaxy, a III‐V semiconductor growth alternative to metalorganic vapor phase epitaxy with the potential to reduce growth costs. The tandem device consists of 3 components: a 1.88 eV band gap (E_G) Ga_0.5In_0.5P top cell, a p‐Ga_0.5In_0.5P/n‐GaAs tunnel junction, and a 1.41 eV rear heterojunction GaAs cell. The open circuit voltage (V_OC) and fill factor are 2.40 V and 88.4%, respectively, indicative of high material quality. Electroluminescence measurements show that the individualV_OCof the top and bottom cell are 1.40 and 1.00 V, respectively, yieldingE_G‐voltage offsets (W_OC) of 0.48 and 0.41 V. TheW_OCof the top cell is higher because of an unpassivated front surface rather than the bulk material quality. The Ga_0.5In_0.5P top cell limits the current of this series‐connected device for this reason to a short‐circuit current density (J_SC) of 11.16 ± 0.15 mA/cm²yielding an overall efficiency of 23.7% ± 0.3%. We show through modeling that thinning the emitter will improve the present result, with a clear pathway toward 30% efficiency with the existing material quality. This result is a promising step toward the realization of high‐efficiency III‐V multijunction devices with reduced growth cost.