Novel symmetric oligomer hole transporting materials (HTMs) incorporating 3,4-ethylenedioxythiophene (EDOT) and 2,1,3-benzothiadiazole (BTD) cores have been synthesized and tested for high performance perovskite solar cells. A maximum energy conversion efficiency of 14.23% has been achieved by employing with the electron donating EDOT unit as the core, which is comparable to that of the traditional (14.55%).

Novel steric bulky hole transporting materials (HTMs) with two or four N,N-di(4-methoxyphenyl)aminophenyl units have been synthesized. When the EtheneTTPA was used as a hole transporting material in perovskite solar cell, the power conversion efficiency afforded 12.77 % under AM 1.5 G illumination, which is comparable to the widely used spiro-OMeTAD based solar cell (13.28 %).

SN(BTTh2)2 and SN(BTAOTh2)2, containing an electron rich planar S,N-heteropentacene flanked with alkoxy substituted and unsubstituted benzothiadiazole and end capped with hexyl-substituted bi-thiophene units, were designed and synthesized.

Two symmetrical star-shaped hole transporting materials (HTMs), i.e. FA-MeOPh and TPA-MeOPh with a fused triphenylamine or triphenylamine core and diphenylethenyl side arms were synthesized. FA-MeOPh showed a strong molar absorption coefficient and a red-shifted absorption compared with TPA-MeOPh because of its planar configuration. The power conversion efficiency (PCE) of the perovskite solar cells based on FA-MeOPh and TPA-MeOPh is about 11.86% and 10.79%, in which the efficiency of former is comparable to that (12.75%) of spiro-OMeTAD based cell. The high photocurrent (18.39 mA cm(-2)) of FA-MeOPh based solar cell relative to TPA-MeOPh based one may be attributable to the enhanced absorption in the near-IR region for mp-TiO2/CH3NH3PbI3/HTM based cell. The high mobility and low series resistance of mp-TiO2/CH3NH3PbI3/FA-MeOPh based cell led to the high fill factor (0.698) of FA-MeOPh based solar cell relative to TPA-MeOPh based one (0.627). In addition, the FA-MeOPh based cell showed a relative stability under light soaking for 250 h. The high efficiency, relative stability, synthetically simple and inexpensive materials as the HTMs hold promise to replace the expensive spiro-OMeTAD.

Increasing global warming is recognized as the most critical issues encountered in this century. Therefore research target at solar energy harvesting is currently under extensive investigation. One promising technology would be organic solar cell, which is expected to dominate the low-cost market in the future. In the organic solar cell, numerous polymers have been used as light harvest. Due to the synthetic difficulty, molecular weight distribution, many research groups have expended endeavors to develop small molecules as the alternative sensitizers, which are easy to the synthesis. Recently, impressive photovoltaic performances have been reported on various well designed small molecules, showing promising efficiency in the range of 5~8.5%. Recently, we synthesized a new series of small molecules with thiophene perylene bisimide, benzothiadiazole, anthracene based chromophore and planar star-shaped unit. In this presentation, we want to report various different type of small molecules for efficient organic solar cells.