Sub-micron Cu(In,Ga)Se2 solar cell with efficiency of 18.2% enabled by a hole transport layer

TL;DR

This paper demonstrates that a hole transport layer can effectively passivate the back contact in sub-micron Cu(In,Ga)Se2 solar cells, achieving over 18% efficiency without the need for a Ga gradient.

Contribution

Introduction of a hole transport layer for back contact passivation, enabling efficient sub-micron Cu(In,Ga)Se2 solar cells without a Ga gradient.

Findings

Achieved over 18% efficiency in sub-micron Cu(In,Ga)Se2 solar cells.

Enhanced open-circuit voltage by 80 mV with hole transport layer passivation.

Attained a fill factor of 77% with the new passivation method.

Abstract

Reducing the thickness of Cu(In,Ga)Se2 solar cells is a key objective in order to reduce production cost and to improve sustainability. The major challenge for sub-micron Cu(In,Ga)Se2 cells is the recombination at the backside. In standard Cu(In,Ga)Se2 backside recombination is suppressed by a bandgap gradient, acting as a back surface field. This gradient is difficult to maintain in sub-micron thick absorbers. In this study, a hole transport layer passivates the back contact and enables efficient sub-micron Cu(In,Ga)Se2 solar cells without the need of a Ga gradient. The backside passivation by the hole transport layer is as effective as an optimized Ga gradient, resulting in a significant increase in open-circuit voltage by 80 mV in comparison to the reference sample without passivation. Moreover, the hole transport layer exhibits good transport properties, leading to a fill factor as high as 77%. Photoluminescence quantum yield of 0.15% and solar cell efficiency above 18% are demonstrated in sub-micron Cu(In,Ga)Se2 absorbers.