Electronic Properties of Photovoltaic CdSe Material

CdSe is potentially an important material for making tandem junction solar cells with Si. It has the right bandgap (1.72 eV) and is a direct gap material. But not much is known about its electronic properties. In this paper, we report on photovoltaic related material properties such as deep defects and minority carrier diffusion length. The films were grown using evaporation. We show that post-deposition annealing in CdCl
₂
vapor significantly improves these properties. Detailed characterization of the material using capacitance-frequency-temperature techniques a deep trap 0.53 eV below the conduction band in the material. Quantum efficiency vs. voltage techniques were used to.yield a value for hole mobility-lifetime (μτ) product in the range of 2×10
^-9
cm
²
/V. The standard device model using a constant range (μτF) where F is the electric field had to be modified to account for the field variation when interpreting QE vs. voltage data to deduce (μτ) product. The as-grown material is generally n-type with doping in the 10
¹⁵
/cm
³
range. Heterojunction devices were made on FTO coated glass substrates using n-CdS as the n-heterojunction layer and organic materials such as PTAA, P3HT and PEDOT:PSS as the p-type heterojunction layer. Urbach energy of tail states was measured using subgap quantum efficiency and was found to be 15 meV.