American Chemical Society
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Enhancing Defect Tolerance and Phase Stability of High-Bandgap Perovskites via Guanidinium Alloying

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journal contribution
posted on 2018-05-02, 00:00 authored by Ryan J. Stoddard, Adharsh Rajagopal, Ray L. Palmer, Ian L. Braly, Alex K.-Y. Jen, Hugh W. Hillhouse
The open-circuit voltages (VOC) of hybrid perovskite (HP) solar cells do not increase sufficiently with increasing bandgap (for Eg > 1.70eV). We study the impact of A+ size mismatch induced lattice distortions (in ABX3 structure) on the optoelectronic quality of high-bandgap HPs and find that the highest quality films have high A-site size-mismatch, where large guanidinium (GA) compensates for small Cs to keep the tolerance factor in the range for the perovskite structure. Specifically, we find that 1.84eV bandgap (FA0.33GA0.19Cs0.47)­Pb­(I0.66Br0.34)3 and 1.75eV bandgap (FA0.58GA0.10Cs0.32)­Pb­(I0.73Br0.27)3 attain quasi-Fermi level splitting of 1.43eV and 1.35eV, respectively, which is >91% of the Shockley-Queisser limit for both cases. Films of 1.75eV bandgap (FA,GA,Cs)­Pb­(I,Br)3 are then used to fabricate p-i-n photovoltaic devices that have a VOC of 1.24 V. This VOC is among the highest VOC reported for any HPs with similar bandgap (1.7 to 1.8 eV) and a substantial improvement for the p-i-n architecture, which is desirable for tandems with Si, CIGS, or a low-bandgap HP. Collectively, our results show that non-radiative recombination rates are reduced in (FA,GA,Cs)­Pb­(I,Br)3 films and prove that FA-GA-Cs alloying is a viable route to attain high VOC in high-bandgap HP solar cells.