PbS/CdS heterojunction quantum dot solar cells

The present work investigates the effects of combination of lead sulfide PbS quantum dots and cadmium sulfide CdS nanoparticles (NPs), with n-type and p-type semiconductors, on the photovoltaic performance of heterojunction solar cells. Namely, p-type semiconductors are: poly[3,4-ethylenedioxythiophene]–poly[styrenesulfonate] (PEDOT:PSS), copper oxide (CuO) NPs and graphene oxide (GO); while n-type semiconductors are: zinc oxide (ZnO) NPs and titanium dioxide (TiO₂) NPs. The above were used to fabricate heterojunction solar cell structures via spin coating, chemical bath deposition and SILAR cycle methods. The morphology and energy band diagram for each solar cell were examined. The photovoltaic performance of the cells was measured under 1 sun illumination (irradiation of 100 mW/cm²). This efficiency ranged between 0.388 and 5.04 %. The solar cell with FTO/ZnO/TiO₂/CdS/PbS/PEDOT:PSS/Au structure and optimum layers’ thickness exhibited a short-circuit current of 24.2 mA/cm², open circuit voltage of 544 mV, a fill factor of 38.2 % and a power conversion efficiency of 5.04 % with reliably good stability. This is related to the uniform surface morphology throughout every cell layer without voids, pinholes or cracks. Furthermore, gradual band energy levels alignment of n-type and p-type NPs (CdS/PbS), as well as high hole mobility of PEDOT:PSS and the high electron affinity of ZnO and TiO₂ are other major factors that controls quantum efficiency.