Research On The Ternary Bulk Heterojunction Organic Solar Cells

The excessive development and consumption of mineral materials have brought a series of problems to the society progress, such as energy shortage, greenhouse effect, acid rain as well as haze. The organic solar cells (OSCs) as a kind of inexpensive renewable energy source has attracted enormous attention because of their easy fabrication, light weight, flexibility, and abundant raw materials. The research on the ternary bulk heterojunction (BHJ) OSCs would become a hot topic since incorporating near infrared region (NIR) low bandgap polymer materials into donor/acceptor system can easily extend the absorption spectral range and improve the photon harvesting. In this paper, we investigated the ternary OSCs based on P3HT:PBDTTT-C:PC71BM and P3HT:DIB-SQ:PC71BM, respectively.The performance of OSCs, based on P3HT and PC71BM, were improved by doping low band gap polymer PBDTTT-C. Power conversion efficiency (PCE) of the ternary blend OSCs is improved to2.48%with6wt%PBDTTT-C, which is27%higher than the binary blend OSCs. The dominant mechanism for the PCE improvement could be attributed to the well balance between photon harvest and charge carrier transport by doping proper concentration PBDTTT-C.It is well know that polymr:polymer blend films generally exhibit macro-scale or micro-scale phase segregation, which have a negative influence on the PCE of OSCs. Therefore, we next studied the influence of small molecule DIB-SQ on the performance of P3HT:PC71BM-based cells. The PCE of the control cells was improved from3.05%to3.72%by doping1.2wt%DIB-SQ as the second donor, which corresponds to about22%PCE enhancement. The energy transfer process from P3HT to DIB-SQ is demonstrated by time-resolved transient photoluminescence spectra through monitoring the lifetime of700nm emission from neat P3HT, DIB-SQ and blended P3HT:DIB-SQ solutions. The lifetime of700nm emission is increased from0.9ns for neat P3HT solution,4.9ns for neat DIB-SQ solution to6.2ns for P3HT:DIB-SQ blend solution.41pictures,4tables, and106references.