Strain Tuning via Larger Cation and Anion Codoping for Efficient and Stable Antimony-Based Solar Cells.

Strain induced by lattice distortion is one of the key factors that affect the photovoltaic performance via increasing defect densities. The unsatisfied power conversion efficiencies (PCEs) of solar cells based on antimony chalcogenides (Sb-Chs) are owing to their photoexcited carriers being self-trapped by the distortion of SbS lattice. However, strain behavior in Sb-Chs-based solar cells has not been investigated. Here, strain tuning in Sb-Chs is demonstrated by simultaneously replacing Sb and S with larger Bi and I ions, respectively. Bi/I codoped SbS cells are fabricated using poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7-(2,1,3-enzothiadiazole)] as the hole-transporting layer. Codoping reduced the bandgap and rendered a bigger tension strain (1.76 × 10) to a relatively smaller compression strain (-1.29 × 10). The 2.5 mol% BiI3 doped SbS cell presented lower trap state energy level than the SbS cell; moreover, this doping amount effectively passivated the trap states. This codoping shows a similar trend even in the low bandgap Sb(SSe) cell, resulting in 7.05% PCE under the standard illumination conditions (100 mW cm), which is one of the top efficiencies in solution processing Sb(SSe) solar cells. Furthermore, the doped cells present higher humidity, thermal and photo stability. This study provides a new strategy for stable Pb-free solar cells.