A roadmap for tandem photovoltaics

Combining two or more junctions into a tandem solar cell promises to deliver a leap in power conversion efficiency that will help to sustain continued growth in installed photovoltaic (PV) capacity. Although tandems are now on the roadmaps of many PV manufacturers, much work remains before they are ready for mass deployment. Accelerating their development requires advances on many fronts. In this article, we outline the fundamentals and status of tandem PV, considering multiple PV technology pairings and architectures. We then present the challenges that must be overcome and a general timeline of activities that are required to translate tandems to commercial products. Our intent is to spur researchers and manufacturers to work together to address important aspects of tandem design, reliability, and scaling to enable more rapid progress toward mass production.