Graphitic carbon nitride quantum dots (g-C3N4) to improve photovoltaic performance of polymer solar cell by combining Förster resonance energy transfer (FRET) and morphological effects

Abstract

In this study, multifunctionality of graphitic carbon nitride quantum dots (g-C3N4 QDs) have been explored as a photovoltaic booster for polymer solar cell. Facile synthesis method of g-C3N4 QDs using organic solvent like o-dichlorobenzene which is commonly used for cell fabrication, has been demonstrated. Photovoltaic effect formation and various effects of QDs on energy transfer, carrier transport and nanoscale film morphology of the devices have been investigated thoroughly by incorporating g-C3N4 QDs as a third component into a well-established material combination of P3HT: PC71BM blend films. While systematic variation of device performances was observed with varying concentration of QDs, at an optimal concentration of 2%, almost 40% performance improvement was achieved compared to the pristine devices. The g-C3N4 QDs were found to assist Förster resonance energy transfer (FRET) between the QDs and host polymer, improving overall energy harvesting capability of the devices. The emission spectra of g-C3N4 QDs (λEms = 400–550) and absorption spectra of P3HT (λAbs = 400–600) were found to have overlapping features which enabled the QDs to transfer ultraviolet region photon energy to P3HT. The g-C3N4 QDs were also found to be favorable for maintaining nanoscale phase segregation of the active layer with improved crystallinity which is crucial for efficient exciton dissociation and faster charge extraction. The enhanced power conversion efficiency thus attributed to the combined consequences of improved morphology and FRET effect. This study opens new prospects for developing high-efficiency solution processable photovoltaic devices using g-C3N4 QDs as the third component of the active layer.