Mechanistic insights on improved performance of PCDTBT:PC 71 BM hetero-structured organic photovoltaic cells via interfacing CdSe/ZnS nanostructures

Correlations among the interface properties, optical absorption, thermal stability and power conversion efficiency (PCE) of organic photovoltaic (OPV) devices are a matter of investigation and need versatile approaches to get better understanding of such issues. In the present study, PCDTBT:PC71BM OPV devices were prepared on the ITO substrates, and the electron extracting electrodes were made of thin Al layers. The functionalization of these devices was done by interfacing the electron acceptor core–shell CdSe/ZnS nanostructures. The reduced electron–hole recombination processes, after interfacing the CdSe/ZnS nanostructures, have resulted in PL intensity quenching of the PCDTBT:PC71BM layer. FE-SEM and HR-TEM images confirm the growth of PC71BM particles as a function of annealing temperatures (100, 120 °C). At lower annealing temperature (100 °C), improved π–π stacking of PCDTBT:PC71BM layer could facilitated the significant charge production and transport which has resulted in higher Jsc values (~ 6.7 mA/cm2) as compared to those from the as-cast PCDTBT:PC71BM layer (4.3 mA/cm2). Interfacing of CdSe/ZnS nanostructures with the PCDTBT:PC71BM layer has resulted in a higher Jsc value (6.8 mA/cm2) which further enhanced to 8.9 mA/cm2, after the heat treatment at 100 °C. A burn-in process induced marginal deterioration in the Jsc and PCE values is also seen in the OPV devices after annealing at higher temperature (120 °C). Maximum PCE of 4.6% is achieved in the PCDTBT:PC71BM@CdSe/ZnS device, when compared with the PCE of PCDTBT:PC71BM basic device (3.2%), for the same operating temperature and annealing time, i.e. 100 °C for a 2 h.