The Polyhedral Specular Reflector: A Spectrum-Splitting Multijunction Design to Achieve Ultrahigh ( >50%) Solar Module Efficiencies

Abstract

The most feasible pathway to record 50% efficiency photovoltaic devices is by utilizing many ( >4) junctions to minimize thermalization and nonabsorption losses. Here we propose a spectrum-splitting design, the polyhedral specular reflector (PSR), that employs an optical architecture to divide and concentrate incident sunlight, allowing the incorporation of more junctions compared with traditional monolithic architectures. This paper describes the PSR design and indicates the requirements to achieve a 50% efficiency module by coupling robust cell, optical, and electrical simulations. We predict that a module comprised of the seven subcells with an average external radiative efficiency of at least 3%, an optical architecture capable of a splitting efficiency of at least 88% and 300× concentration, small ( $\boldsymbol{\leq }$ 1 $\mathrm{\boldsymbol{\mu }}$ m) metallic fingers for subcell contact, and a state-of-the-art power conditioning system ( >98% efficiency) can achieve a module efficiency of 50%, a record for both multijunction cells and modules. We also discuss the flexibility of the design and explore how adjusting the size and type of concentrators can still yield record module efficiencies ( >40%).