Lead-free formamidinium bismuth perovskites (FA)3Bi2I9 with low bandgap for potential photovoltaic application

Single- or double A-site cations in A3Bi2I9 bismuth perovskites: What is the suitable choice?

“…In comparison to MA 3 Bi 2 I 9 , FA 3 Bi 2 I 9 shows a similar XRD pattern to MA 3 Bi 2 I 9 with a preferential orientation along the (011) plane (Fig. 2a, blue trace) and is in line with the previous report by Lan et al [29] For the DMA 3 Bi 2 I 9 case, there is a slight shift of all peaks towards smaller 2θ angles, which is most probably due to the larger ionic radius of the DMA + compared to MA + cation (r DMA+ = 272 pm vs. r MA+ = 217 pm) (Fig. 2a, cyan trace).…”

“…The solar cell parameters from champion devices with organic-inorganic bismuth iodides are listed in Table S3 and the box plot of device parameters is shown in Figure S9. FA 3 Bi 2 I 9 solar cells achieved 0.02% PCE and an opencircuit voltage (V OC ) of 0.51 V, which is higher than the previous report for FA 3 Bi 2 I 9 processed from DMF solution [29]. DMA 3 Bi 2 I 9 and GA 3 Bi 2 I 9 show photovoltaic activity, however, the efficiency was low due to the comparatively low short circuit current (J SC < 0.1 mA/cm 2 ) and lower V OC < 0.55 V. Figure 6b presents the champion J-V curves of all-inorganic bismuth halides, where Cs 3 Bi 2 I 9 based solar cells show the best performance (PCE of reverse scan 0.24%, Table S4) compared to rubidium-, potassium-and sodium-based bismuth iodide absorber based solar cells, which showed PCE up to 0.15% (Table S4).…”

“…Subsequently, efforts have been made to further improve the efficiency by employing suitable electron transport layers [25], vapour deposition [26], solvent engineering [27]; however, the efficiency has been limited. Nevertheless, various solution-based and vaporassisted methods were reported with different solvents [27,28] and fabrication processes leading to PCEs between 0.01% [29] and 1.64% [30]. Efforts have also been made to develop bismuth perovskite with alternative A-site cations.…”

Scalable Production of Ambient Stable Hybrid Bismuth‐Based Materials: AACVD of Phenethylammonium Bismuth Iodide Films**

“…The existence of aromatic cations causes quantum confinement in the perovskite materials, band gap widening and resulting in deposited films with different colors [47] . Even though efficiencies have not matched those of lead‐based PSCs, the relatively large bandgap and high stability of bismuth hybrid materials with bulky organic ligands, such as phenethylammonium bismuth iodide or [PEA] 3 [Bi 2 I 9 ] (Figure 1c), make them ideal candidates for tandem solar cells, acting as wide‐band‐gap top cell in combination with lower bandgap semiconductors for example silicon, CIGS/Se or perovskites [23,48] . Furthermore, their high resistivity and thermal stability make them potential candidates as high‐performance X‐ray detectors, [49,50] and in many other cutting‐edge applications such as photosensing and aqueous battery systems, [51,52] making their further development extremely interesting.…”

“… [47] Even though efficiencies have not matched those of lead‐based PSCs, the relatively large bandgap and high stability of bismuth hybrid materials with bulky organic ligands, such as phenethylammonium bismuth iodide or [PEA] 3 [Bi 2 I 9 ] (Figure 1 c), make them ideal candidates for tandem solar cells, acting as wide‐band‐gap top cell in combination with lower bandgap semiconductors for example silicon, CIGS/Se or perovskites. [ 23 , 48 ] Furthermore, their high resistivity and thermal stability make them potential candidates as high‐performance X‐ray detectors,[ 49 , 50 ] and in many other cutting‐edge applications such as photosensing and aqueous battery systems,[ 51 , 52 ] making their further development extremely interesting. Despite having a large potential span of applicability, the lack of a scalable and cost‐effective synthetic process for this class of materials represents a large liability for their development and commercialization.…”