Gun Dae Lee

2,6-pyridinedimethanol (Py-diOH) is applied to the cathode interlayer in inverted polymer solar cells (PSCs) based on the blend of PTB7:PC₇₁BM. A layer of Py-diOH generates a favorable interface dipole at the cathode interface. The power conversion efficiency of the devices with the interlayer reaches up to 7.44% with a J_sc of 14.65 mA/cm², a V_oc of 0.71 V, and a FF of 67.9%, respectively The PCE of the device with Py-2OH is very similar to that of the device with ZnO as the electron collection layer. It is possible to obtain high efficiency PSCs without any high temperature heat treatment.

Two newly designed donor-acceptor (D-A) conjugated polymers were prepared from the Stille coupling reactions by incorporating phthalimide derivative as a co-acceptor unit into 2,1,3-benzooxadiazole (BO) and thiophene with different ratios of 5 mol.% and 10 mol.% of TBO-I 5, TBO-I 10, respectively. Polymers possess moderate molecular weights and excellent thermal properties with a 5% weight loss temperatures (T_d) around 300°C. Compared to poly{5,6-bis(decyloxy)-4-(thiophen-2-yl)benzo[c][1,2,5]oxadiazole} (TBO), adding phthalimide unit in TBO-I 5 and TBO-I 10 shifted UV-Vis absorption spectra and changed the HOMO and LUMO levels of polymers. Bulk hetero junction (BHJ) polymer solar cells (PSCs) based on polymers blended with [6,6]-phenyl-C61-butyric acid methyl ester (PC₆₁BM) were fabricated to investigate photovoltaic properties. As a results, with increasing the composition of phthalimide, the J_sc of the devices based on polymers were reduced in the order of TBO (4.74 mA/cm²) > TBO-I 5 (3.94 mA/cm²) > TBO-I 10 (1.90 mA/cm²) due to the blue-shifted in absorption spectra and twisting in polymer main chain of TBO-I polymers. The decrease in J_sc led to low photovoltaic performances and the device based on TBO showed higher performances than those of TBO-I 5 and TBO-I 10 with the PCE of 1.66%, the J_sc of 4.74 mA/cm², the V_oc of 0.82 V and the FF of 42.4% under the illumination of AM 1.5G, 100 mW/cm².