Tandem Solar Cells from Solution-Processed CdTe and PbS Quantum Dots Using a ZnTe–ZnO Tunnel Junction

• Published in: Nano letters 2017-02, Vol.17 (2), p.1020-1027
• Main Authors: Crisp, Ryan W, Pach, Gregory F, Kurley, J. Matthew, France, Ryan M, Reese, Matthew O, Nanayakkara, Sanjini U, MacLeod, Bradley A, Talapin, Dmitri V, Beard, Matthew C, Luther, Joseph M
• Format: Article
• Language: English
• Subjects: multijunction; nanocrystals; NANOSCIENCE AND NANOTECHNOLOGY; photovoltaics; quantum dots; solar cell; SOLAR ENERGY; tandem
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.6b04423

We developed a monolithic CdTe–PbS tandem solar cell architecture in which both the CdTe and PbS absorber layers are solution-processed from nanocrystal inks. Due to their tunable nature, PbS quantum dots (QDs), with a controllable band gap between 0.4 and ∼1.6 eV, are a promising candidate for a bottom absorber layer in tandem photovoltaics. In the detailed balance limit, the ideal configuration of a CdTe (E g = 1.5 eV)–PbS tandem structure assumes infinite thickness of the absorber layers and requires the PbS band gap to be 0.75 eV to theoretically achieve a power conversion efficiency (PCE) of 45%. However, modeling shows that by allowing the thickness of the CdTe layer to vary, a tandem with efficiency over 40% is achievable using bottom cell band gaps ranging from 0.68 and 1.16 eV. In a first step toward developing this technology, we explore CdTe–PbS tandem devices by developing a ZnTe–ZnO tunnel junction, which appropriately combines the two subcells in series. We examine the basic characteristics of the solar cells as a function of layer thickness and bottom-cell band gap and demonstrate open-circuit voltages in excess of 1.1 V with matched short circuit current density of 10 mA/cm2 in prototype devices.