Interfacial modification by conjugated polyelectrolytes with amino acid groups in perovskite solar cells

The defects in perovskite MAPbI3 film act as non-radiative recombination centers of charge carriers, adversely affecting the performance of perovskite solar cells (PSCs). Herein, two conjugated polyelectrolytes containing amino acid groups, thiophene-carbazole copolymer (POWTC) and thiophene-fluorene copolymer (POWTF), are introduced to modify perovskite film by anti-solvent method. XPS and FTIR characteristics demonstrate the formation of chemical bonding between amino acid groups and the uncoordinated Pb2+ cations and I- anions which leads to efficient defect passivation of MAPbI3 film. The quality of the perovskite film is clearly improved due to the polyelectrolytes being involved in the perovskite crystallization process. Under this dual-function mechanism, PSCs with POWTC and POWTF deliver the enhancement of efficiency and operational stability. POWTF with higher molecular weight functions better than POWTC. The POWTF-modified cell presents power conversion efficiency (PCE) of 21.41% with open circuit voltage (VOC) of 1.13 V and a short-circuit current density (JSC) of 24.17 mA cm-2, superior to 19.22% of the control cell. The unencapsulated POWTF cell retains 85% of its original PCE, while the control cell only retains about 50% of its original PCE, after aging for 500 h under ambient atmosphere with 40-50% relative humidity in the dark.