Beier Hu1
Imperial College London1
Intraband trap states can be formed unavoidably during the solution-processed fabrication of perovskite solar cells (PeSCs). Their existence contributes to non-radiative recombination loss via trap-assisted recombination pathways in PeSCs, leading to insufficient power conversion as well as a higherIntraband trap states can be formed unavoidably during the solution-processed fabrication of perovskite solar cells (PeSCs). Their existence contributes to non-radiative recombination loss via trap-assisted recombination pathways in PeSCs, leading to insufficient power conversion as well as a higher probability of lattice decomposition. Particularly, regarding the soft nature of perovskites, one should consider the impact of local lattice strain on the properties of trap states. However, the relationship between strain and trap-assisted recombination has not been disclosed systematically and comprehensively. <br/><br/>Herein, we fabricated two perovskite films with different strain levels, i.e., MA<sub>0.95</sub>GA<sub>0.05</sub>PbI<sub>3</sub> with tensile strain and MA<sub>0.95</sub>GA<sub>0.05</sub>Pb(I<sub>0.95</sub>Br<sub>0.05</sub>)<sub>3</sub> with free strain due to the compensation of the smaller-size Br towards the expanded lattice. To access the critical factors that affect the trap-assisted recombination including the number of traps, depth of traps, and lifetime of trapped carriers, we employed the advanced visible-pump-IR-push photocurrent spectroscopy (PPPc) on devices based on the aforementioned perovskite films with and without strain. PPPc is a highly selective technique for observing localized state behaviours of PeSCs under operational conditions, to display a full scenario of the regulated trapped carrier dynamics after strain manipulation. Steady-state and time-resolved PPPc measurements evidenced that the strain relaxation was able to reduce the density of traps, shallow the depth of traps, and prolong the lifetime of trapped carriers, alleviating the trap-assisted recombination loss in the strain-free device. To the best of our knowledge, this is the first report which provides an explicit correlation between strain engineering and its impacts on the overall trap-assisted recombination processes.