Copper selenide as a new counter electrode for zinc oxide nanorod based quantum dot solar cells

• Jsc is increased from 6.02 mA/cm2 to 11.26 mA/cm2 using Cu2Se counter electrode.
• The maximum η 2.28%, is achieved in QDSSCs when cycle of Cu2Se is 5.
• The Rct is reduced by the changing counter electrode from CuS to Cu2Se.

This work investigates the improvement in efficiency of quantum dot sensitized solar cells (QDSSCs) using copper selenide (Cu2Se) as a new counter electrode. Cu2Se counter-based QDSSC exhibits power conversion efficiency (η) of 2.28%, which is higher than the 1.17% efficiency of copper sulfide (CuS) counter electrode. Electrochemical impedance spectroscopy results show that by the changing counter electrode from CuS to Cu2Se, the charge transfer resistance at the counter electrode/electrolyte interfaces is reduced and, consequently, causes current density rise from 6.02 mA/cm2 to 11.26 mA/cm2. Also, open circuit voltage decay and dark current density–voltage results show that the lifetime of electron in the Cu2Se counter-based QDSSC is higher than that of QDSSC with CuS counter electrode. Therefore, Cu2Se counter electrode can be regarded as a promising alternative to the noble CuS counter electrode in QDSSCs.