Efficiency versus effort: a better way to compare best photovoltaic research cell efficiencies?

TL;DR

This paper proposes using cumulative publications as a proxy for R&D effort to compare photovoltaic technologies, revealing similar efficiency learning curves and insights into effort versus performance trends.

Contribution

It introduces a novel metric based on publication count to analyze PV technology progress, offering a new perspective beyond traditional efficiency trends.

Findings

Silicon, CIGSe, CdTe, and halide perovskites follow similar efficiency learning curves.

Efficiency improvements show a consistent 5% increase per tenfold increase in publications.

Plateaus in efficiency may indicate fundamental barriers to further progress.

Abstract

Frequently, trends in record AM1.5 power-conversion efficiencies versus time, such as the NREL efficiency chart, are used to analyze the relative merits of different photovoltaic material technologies. However, this approach belies the effort expended in achieving these levels of performance. We introduce cumulative publications as a proxy for total R&D efforts and find surprisingly that silicon, Cu(In,Ga)Se2 (CIGSe), CdTe, and halide perovskite technologies have each followed essentially the same learning curve of 20-24% efficiency within 10,000 publications and a consistent marginal rate of 5% efficiency increase per factor of 10 in publications. While learning spillover from non-PV technologies, cross-pollination from other PV technologies, and hidden commercial effort are not accounted for by this metric, this analysis still yields useful and novel insights into PV technology trajectories. Trajectories below this learning curve have required more total effort per performance and plateaus of efficiency stagnation at large numbers of publications may indicate (but do not guarantee) the existence of fundamental barriers to commercially relevant performance. Lastly, examples to watch are identified for technologies currently exhibiting higher marginal slopes, including some that appeared dormant by this metric in past years.