Research On The Novel Donor Materials & Properties Of Organic Bulk Heterojunction Solar Cell

Bulk heterojunction (BHJ) organic solar cell become one of the promising ways for solar energy and being widely concerned due to higher power conversion efficiencies (PCE), ease of prepared and the potential of producing large scale flexible devices. However due to the low carrier mobility of the organic semiconductor materials and the problem of separation, transport and collection of the charge carriers, PCE of the whole device is still low. So we synthesize a new type of low band gap, high carrier mobility organic semiconductor materials for organic photovoltaic cells, and optimized the fabrication of the device to obtain higher PCE.1. We fabricate BHJ solar cell device based on oligothiophene derivative DCN5T and (6,6)-phenyl C61 butyric acid methyl ester (PCBM) with a device structure of ITO (～17Ωsq-1) / PEDOT: PSS (40 nm) / DCN5T:PCBM (110 nm) / LiF (1 nm) /Al (70 nm). After optimizing the donor-acceptor weight ratio, we get a PCE of 0.69% with the weight ratio of 1:1.4. The film exhibits more continuous interpenetrating network morphology than others. Also we fabricate different organic solar cell devices based on DCN3T, DCN5T, DCN7T and PCBM as active layers respectively. The performance of these devices is improved with the oligothienyl chain lenrth, which implied the chain length can tune the solar cell performance. These novel soluble oligothiophene provide an attractive avenue for the research of BHJ organic solar cell.2. We further fabricate BHJ solar cell based on a novel oligothiophene derivative DCN7T and PCBM as active layer. The oligothiophene composes of thiophene rings substituted with two terminal di-CN electron-withdrawing end groups form a (D-A) structure, which increases the absorption in the visible spectrum and improves charge carrier transport in photovoltaic devices. When the DCN7T: PCBM with weight ratio of 1:1.4 under simulated AM 1.5 G 100 mW/cm2 illuminations. The PCE of 3.7 % is achieved, Voc of 0.88V and Jsc of 12.4mA/ cm2 which is among the best PCE of solution processed small molecule BHJ solar cells.3. We successfully fabricate the BHJ organic solar cell based on grapheme and PEDOT: PSS composites buffer laer with a structure of ITO / PEDOT: PSS: Graphene/P3HT: PCBM / LiF / Al. The pre-annealing treatment graphene 250℃10min dissolved in to PEDOT: PSS with ultrasonic method. We use this composites as buffer layer to modify the pristine devices, and the PCE of 3.8% is achieved, Jsc of 14.2 mA/cm2,Voc of 0.62V,and FF of 0.43. The addition of graphene makes energy conversion efficiency 1.8 times that of the device based on a pristine PEDOT: PSS buffer layer.