Simulation and partial prototyping of an eight‐junction holographic spectrum‐splitting photovoltaic module

Sunita Darbe,Matthew D Escarra,Harry A Atwater,Emily C Warmann

doi:10.1002/ese3.445

Sunita Darbe, Matthew D Escarra + Show 2 more

Open Access

https://doi.org/10.1002/ese3.445

Copy DOI

Abstract

AbstractSpectrum‐splitting photovoltaics incorporate optical elements to separate sunlight into frequency bands, which can be targeted at solar cells with bandgaps optimized for each sub‐band. Here, we present the design of a holographic diffraction grating‐based spectrum‐splitting photovoltaic module integrating eight III‐V compound semiconductor cells as four dual‐junction tandems. Four stacks of simple sinusoidal volume phase holographic diffraction gratings each simultaneously split and concentrate sunlight onto cells with bandgaps spanning the solar spectrum. The high‐efficiency cells get an additional performance boost from concentration incorporated using a single or a compound trough concentrator, providing up to 380X total concentration. Cell bandgap optimization incorporated an experimentally derived bandgap‐dependent external radiative efficiency function. Simulations show 33.2% module conversion efficiency is achievable. One grating stack is experimentally fabricated and characterized.

Highlights

Over 40% of solar power incident on a single‐junction solar cell is lost due to two main causes
We incorporate eight subcells as four dual junctions and use a compound parabolic concentrator (CPC) for external concentration. We introduced this design concept, which uses a higher number of subcells than any previous effort, in prior work,[14,15] where we showed that larger numbers of subcells are necessary to achieve very high‐efficiency photovoltaics
The spectral separation of the four‐stack holographic optical element is shown in Figure 3B, where the fraction of incident light hitting each of the four subcells is shown

Summary

Introduction

Over 40% of solar power incident on a single‐junction solar cell is lost due to two main causes. The excess energy of photons of higher energy than necessary to promote an electron from the valence band to the conduction band is lost as heat.[1] Two main strategies are used today to address these losses: conventional tandem multijunction photovoltaic systems and spectrum‐splitting optical approaches. Both strategies attempt to prevent these losses by incorporating multiple absorbers of different bandgap energies in order to absorb photons with reduced losses. Independent connection is easier to achieve through lateral spectrum splitting in which external optical elements are used to separate spectral bands

Objectives

Results

Conclusion