Current–voltage (J–V) characteristics of the devices were mea- sured using a Keithley 2400 source meter connected with a GPIB controller to a computer under one sun illumination (AM1.5, 100 mW/cm2). The incident photo to current conversion efficiency (IPCE) spectra was performed with Stanford SR803 lock-in ampli- fier under monochromatic illumination at a chopping frequency of 130 Hz by a Stanford SR540 chopper. All the measurements were carried out at room temperature under ambient conditions.