Improvement of CIS Solar Cells with KF Postdeposition Following a Simple Two-Step Selenization Process

Abstract

A CuInSe2 (CIS) thin film solar cell (without Ga) with 14.7% efficiency is demonstrated based on the use of a potassium fluoride (KF) post-deposition treatment (PDT). By comparison, a CIS solar cell with 10.3 % efficiency is obtained without KF PDT. No anti-reflection (AR) coating was used. KF PDT helps to form a hole-blocking layer between CdS/CIS interface and reduce the symmetry of the non-ohmic shunt leakage at low forward bias and reverse bias. The hole-blocking layer reduces the tunneling recombination and significantly increases the open circuit voltage. A space charge limited (SCL) current model is used to explain the symmetry feature of the current vs voltage, which is indicative of metal-semiconductor-metal (MSM) shunts. To understand possible defects and shunt path, some discussion is presented.