The PV Efficiency vs R&D Effort Learning Curve for Research-Stage Material Technologies

The traj ectory of PV technologies are frequently presented and discussed in terms of record efficiency versus date, or for commercialized technologies, also in terms of learning curves showing cost or price versus total number of modules. For early-stage PV material technologies, efficiencies are typically low and of course no modules have been produced. We introduce a different learning curve appropriate for assessing the trajectories of PV technologies still in the R&D stage; efficiency as function of total publications which aims to capure total R&D effort for each technology. The premise was that material technologies that were intrinsically better for PV should give more efficiency for lower total effort. Incredibly, the trajectories of many major single-junction cell technologies - Si, CIGSe, CdTe, and halide perovskites - all follow the same curve. The curve is logarithmic, capturing the common-sense idea that each limiting problem for a PV technology is harder than the last (diminishing returns). We present the trajectories of many common single-junction technologies and discuss insights gained from analyzing their trajectories through this different lens. We present this learning curve and give our own discussions and speculations on factors affecting trajectories and implications from the analysis. We hope to spark interesting discussions and further analyses by presenting the work.