Study On The Double Subjects Ternary Polymer Organic Solar Cell

Polymer solar cells (PSCs) developed as one of the most potential new energy technology, due to its low cost, flexible manufacturing and the possibility of producing. Improving power conversion efficiency is the destination in the study of PSCs. Recently, ternary bulk-heterojunction (BHJ) polymer solar cells (PSCs) are emerging as an attractive strategy with simple fabrication technology to extend the spectral of wide bandgap polymers into the near infrared (NIR) region by adding a narrow bandgap sensitizer. In this letter, we made two different polymer ternary bulk-heterojunction (BHJ) polymer solar cells (PSCs) based on "two donor one acceptor" and study the effect of the third material on the performance of PSCs.Frist, a series cells including binary BHJ-PSCs with P3HT:PCBM as the active layer (control cell) and ternary BHJ-PSCs with different PTB7-Th doping concentrations were fabricated to investigate the effect of PTB7-Th on the performance of PSCs. The short circuit current density (Jsc), fill factor (FF) of the ternary PSCs were simultaneously improved by adding a small amount of PTB7-Th into P3HT:PCBM. The champion PCE of ternary PSCs (with 15wt% PTB7-Th) is 3.71%, which is larger than 2.71% of the control cell. In ternary devices, the absorption region showed a distinct red-shift and the relative absorption intensity from 650 nm to 800 nm was gradually enhanced along with the increasing of PTB7-Th doping concentration. The increased photon harvesting in the solar spectral range resulted in an increased short-circuit current density (Jsc). However, despite the PL spectrum of P3HT has a large overlap with the absorption spectra of PTB7-Th, which makes it possible for Forster resonance energy transfer (FRET) between P3HT and PTB7-Th, the PL suggested that the main mechanism between PTB7-Th and P3HT is photo-induced electron transfer from P3HT to PTB7-Th (hole transfer from PTB7-Th to P3HT), not energy transfer. The PSCs with P3HT:PTB7-Th (1:1) as the active layer display a larger Jsc compared with that of P3HT-based, when the concentration of PTB7-Th was reduced and the concentration of P3HT was unchanged (P3HT:PTB7-Th 1:0.5), the Jsc can be future enhancement. The increased Jsc values of P3HT:PTB7-Th (1:0.5) PSCs confirmed that the photo-generated excitons can be dissociated into free charge carriers at the P3HT:PTB7-Th interface and reinforced the charge transfer between P3HT and PTB7-Th. In P3HT:PCBM binary organic solar cell, the photo-generated excitons only can be directly dissociated into free charge carriers at the P3HT:PCBM interface and then transported to the respective electrodes, while incorporating PTB7-Th, the interaction between P3HT and PTB7-Th also make the photo-generated excitons can be dissociated at the interface of P3HT:PTB7-Th and PTB7-Th:PCBM. The increasing of excitons dissociated led to a higher FF.Second, We demonstrate an effective ternary bulk-heterojunction (BHJ) polymer solar cells (PSCs) by incorporating donor material poly[N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-2’,1’,3’benzothiadiazole) (PCDTBT) into a poly[[4,8-bis[(2-ethylhexyl)-oxy]benzo[1,2-b:4,5-b0]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-diyl]] (PTB7):fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) host binary blend without additives and study the effect of PCDTBT on the PSCs. The power conversion efficiency (PCE) of PSCs was improved from 5.23% to 6.73% by doping 10 wt% PCDTBT due to the improvement of the fill factor (FF) and the short-circuit current density (Jsc). Because PTB7 can efficiently absorb photons at long wavelengths and PCDTBT can efficiently absorb photons at short wavelengths, the absorb photons of PSCs can be adjusted by adjusting the doping ratios of two donors. The better trade-off photon harvesting in the whole spectral range improved the performance of PSCs. The ratio of hole and electron mobility in PTB7:PCBM is 5.55, in PCDTBT:PCBM is 6.23, and in film with 10 wt% PCDTBT is 2.02 which is lower than the control one. The balanced hole and electron transportation in ternary PSCs reduced the formation of space charges in devices, that is beneficial for mitigating the charge recombination and a higher FF value of the corresponding PSCs is obtained.