Cooperative effects of Dopant-Free Hole-Transporting materials and polycarbonate film for sustainable perovskite solar cells

Dopant-free hole-transporting materials (HTMs) and interface modification are two effective approaches for developing sustainable perovskite solar cells (PSCs). In this work, dopant-free HTM (GW-4) containing an N- ethyl-carbazole with two rotatable vinyl linkages is first synthesized by a green chemical method without any metal catalysts. The GW-4 cost is only 22.43% of the price of commercial 2,2'7,7'-tetrakis[N,N-di(4-methox-yphenyl)amino]-9,9 & PRIME;-spirobifluorene (spiro-OMeTAD). In the device fabrication, the concentrations of doped GW-4 (20 mg mL(-1)) and pristine GW-4 solutions (10 mg mL(-1)) are much lower than that of spiro-OMeTAD solution (doped, 72.3 mg mL-1). The power conversion efficiency (PCE) of doped GW-4-based cell is 20.45%, superior to that of spiro-OMeTAD-based cell (19.59%). As the optimal concentration of dopant-free GW-4 is insufficient to completely cover the perovskite layer, a polycarbonate (PC) polymer with carbonyl groups is first introduced to modulate perovskite grain boundaries and improve film-forming property of pristine GW-4. The cell with PC/pristine GW-4 has a slightly higher PCE (17.92%) than the cell with pristine GW-4 (17.66%). Regarding humid stability, after 455 h, the doped GW-4 and spiro-OMeTAD based PSCs retain only 11.71% and 2.27% of the initial efficiency, respectively. In striking contrast, after 850 h, the pristine GW-4 and PC/pristine GW-4 based devices retain 69.74% and 97.53% of the initial efficiency, respectively. This study provides both a new molecular design strategy to develop highly efficient dopant-free HTMs and an ingenious interfacial contrivance to overcome the defects of incomplete coverage of HTM film on perovskite layer and understand the charge dynamics at interfacial layers.

Automated summary

Dopant-free hole-transporting materials (HTMs) and interface modification are effective approaches for sustainable perovskite solar cells (PSCs). This study successfully synthesized a low-cost dopant-free HTM and improved its film-forming property by introducing a polycarbonate (PC) polymer. The results showed that the PCE of the doped GW-4-based cell was higher than that of the spiro-OMeTAD-based cell, and the PC/pristine GW-4-based device exhibited good humidity stability.