Beyond 8% ultrathin kesterite Cu2ZnSnS4 solar cells by interface reaction route controlling and self-organized nanopattern at the back contact

Fangyang Liu,Xu Liu,John A Stride,Fangzhou Zhou,Xiaojing Hao,Chang Yan,Jongsung Park,Martin A Green,Yansong Shen,Aobo Pu,Jialiang Huang,Kaiwen Sun

doi:10.1038/am.2017.103

Abstract

Highly efficient, ultrathin (~400 nm) pure sulfide kesterite Cu2ZnSnS4 (CZTS) solar cells have been realized by interface reaction route controlling and self-organized nano-pattern at the back contact. The Al2O3 intermediate layer introduced at the Mo/CZTS interface can effectively inhibit the detrimental interfacial reaction between CZTS and Mo in the initial stage of sulfurization, and then turns into a self-organized nanopattern yielding a nanoscale opening for electrical contact. With this interface modification, the traditional issues of phase segregation (secondary phases) and voids at the back contact region can be well addressed, which greatly improves uniformity and reduces back contact recombination. As a result, this interface modification not only leads to beyond 8% ultrathin CZTS solar cells but also yields two certificated world record efficiencies: 9.26% for 0.237 cm2 small area and 7.61% for 1 cm2 standard kesterite CZTS solar cells (normal thickness).

Highlights

The semiconductor kesterite Cu2ZnSnS4 (CZTS) has attracted worldwide attention owing to its similarities with already commercialized direct gap absorbers such as CdTe and Cu(In,Ga)Se2 (CIGSe), while having only earth-abundant and environmentally friendly constituents
According to previous experience in ultrathin CIGSe solar cells, this issue of optical losses can be minimized by improved back contact reflectivity[8,9] and implementation of light trapping,[10,11,12] both of which could be well used in the case of ultrathin CZTS
We report ultrathin (~400 nm) Se-free kesterite CZTS solar cells of 4 8% efficiency, realized by inserting an ultrathin dielectric intermediate layer into the Mo/CZTS interface

Summary

Introduction

The semiconductor kesterite Cu2ZnSnS4 (CZTS) has attracted worldwide attention owing to its similarities with already commercialized direct gap absorbers such as CdTe and Cu(In,Ga)Se2 (CIGSe), while having only earth-abundant and environmentally friendly constituents. The Al2O3 intermediate layer introduced at the Mo/CZTS interface can effectively inhibit the detrimental interfacial reaction between CZTS and Mo in the initial stage of sulfurization, and turns into a self-organized nanopattern yielding a nanoscale opening for electrical contact.

Results

Conclusion