Effect of double substitutions of Cd and Cu on optical band gap and electrical properties of non-colloidal PbS thin films

•Double substitutions of noncolloidal PbS thin films with Cd and Cu were studied.•Single step chemical bath deposition was conducted for (Pb1−xCdx)1−yCuyS films.•Band gap tunability from 1.22 to 1.78 eV was achieved with the Cd/Cu substitutions.•The optimal film of (Pb0.8Cd0.2)0.9Cu0.1S showed an ideal band gap of 1.63 eV.•Excessive Cu was not desirable due to unstable growth and high carrier concentration.

Controllable band gap has been pursued to absorb a proper range of light by p-type absorber semiconductors for better performance photovoltaic devices. Here we introduce double substitutions with Cd and Cu for non-colloidal p-type PbS thin films to cover a broader range of optical band gap from 1.22 to 1.78 eV. Thin films of (Pb1−xCdx)1−yCuyS (x = 0–0.3 and y = 0–0.3) were grown by a single step chemical bath deposition process at a low temperature of 70 °C. The incorporation of Cd resulted in a wider band gap but changed the type of semiconductor into n-type above x = 0.2. Only the proper substitutions with both Cd and Cu induced an optimal band gap of 1.63 eV, which means a substantial improvement compared to 1.22 eV for pure PbS thin film, while maintaining p-type conductivity. Interestingly, excessive Cu substitutions beyond y = 0.2 inhibited crystallization significantly and generated an undesirably high carrier concentration.