Annihilation of structural defects in chalcogenide absorber films for high-efficiency solar cells

Roland Mainz,Isaac Balberg,Marc D Heinemann,Manuela Klaus,Peter A Van Aken,Daniel Abou-Ras,Stephan Brunken,Christian A Kaufmann,Shir Hajaj,Ekin Simsek Sanli,Quentin M Ramasse,Oded Millo,Alfons Weber,Helena Stange,Humberto Rodriguez-Alvarez,Dieter Greiner,Doron Azulay

doi:10.1039/c6ee00402d

Abstract

Defects rapidly annihilate near stoichiometric composition.

Highlights

Low-temperature fabrication of semiconductor films for solar cells and other applications reduces the energy consumption during fabrication and enables the use of substrates with limited temperature tolerance, such as light-weight and flexible polyimide foils, and has the potential to enhance the competitiveness and scale-up of solar power.[1]
For the sample processed with a Cu-rich stage, Cu–Se deposition was continued until a Cu-rich composition was reached, and subsequently the composition turned Cu-poor by final In–Ga–Se deposition. (For more details on the film synthesis see Methods.)
A small-grained top layer (Fig. 1b) is attributed to the final In–Ga–Se deposition stage (Fig. S1b, Electronic supplementary information (ESI)†), which changes the composition back to Cupoor. (Additional bright-field transmission electron microscopy (TEM) images confirming the findings shown in Fig. 1a and b can be found in Fig. S2, ESI.†)

Summary

Introduction

Low-temperature fabrication of semiconductor films for solar cells and other applications reduces the energy consumption during fabrication and enables the use of substrates with limited temperature tolerance, such as light-weight and flexible polyimide foils, and has the potential to enhance the competitiveness and scale-up of solar power.[1]. Remarkable success in increasing the power-conversion efficiencies of solar cells based on lowtemperature (o500 1C) deposited Cu(In,Ga)Se2 (CIGSe) to the world-record level has been recently achieved.[6,7] Even though a Cu-poor composition ([Cu]/([In] + [Ga]) o 1) is needed for high efficiencies, at low temperatures as well as moderate temperatures (B530 1C) the synthesis of high-quality CIGSe relies on a complex three-stage co-evaporation process in which the film takes a detour via an intermediate Cu-rich composition ([Cu]/ ([In] + [Ga]) 4 1).[8] In this process, the optoelectronic properties and solar cell efficiencies are improved by the intermediate Cu-rich process stage, realized by the deposition of Cu–Se in excess.[9,10] Despite the fact that this phenomenon has been known for more than two decades,[8,11,12] the nature of the mechanism responsible for this efficiency improvement is not yet fully accounted for In this contribution we provide novel insights into the nature and dynamics of the mechanism responsible for the improvement of the film quality during CIGSe growth

Methods

Results

Conclusion