Hole transport material, synthesis thereof, and solar cell

The organic small molecule 4,4',4",4"'-(5,5-dimethoxycyclopenta-1,3-diene-1,2,3,4-tetrayl)tetrakis(N,N-bis(4-methoxyhenyl)aniline (CPDA 1), shows electrochemical properties very close to spiro-OMeTAD indicating a high compatibility with PSC systems for its use as a hole transport material (HTM). The implementation of the cyclopentadiene dimethyl acetale core helps to red shift the absorption onset of the films as well as provide a flexible spatial configuration of the molecule, which is essential for optimum film forming properties. Transient and steady state emission analysis as well as hole mobility measurements indicate that the new HTM allows a better charge extraction, transport and separation than the spiro-OMeTAD reference compound. PSCs based on the new CPDA 1 show a PCE close to 23% with lower hysteresis than its analogue. Stability studies performed under ambient, heated and humid conditions all showed that CPDA 1 is over-performing spiro-OMeTAD. Furthermore the production cost of CPDA 1 is about 10 times lower than that of spiro-OMeTAD, contributing to render PSCs more affordable.