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.