V_OC Over 1.4 V for Amorphous Tin-Oxide-Based Dopant-Free CsPbI₂Br Perovskite Solar Cells

Abstract

CsPbI2Br perovskite solar cells have attracted much attention because of the rapid development in their efficiency and their great potential as a top cell of tandem solar cells. However, the V OC outputs observed so far in most cases are far from that desired for a top cell. Up to now, with various kinds of treatments, the reported champion V OC is only 1.32 V, with a V OC deficit of 0.60 V. In this work, we found that aging of the SnCl2 precursor solution for the electron-transporting layer can promote the V OC of CsPbI2Br solar cells by employing a dopant-free-polymer hole transport material (HTM) over 1.40 V and efficiency over 15.5% with high reproducibility. With the champion V OC of 1.43 V, the V OC deficit was reduced to <0.50 V, which is achieved for the first time. This simple technique of SnCl2 solution aging forms a uniform and smooth amorphous SnO x film with pure Sn4+, elevates the conduction band of SnO x , and reduces the interfacial gaps and the trap state density of the device, resulting in enhancement in average V OC from ∼1.2 V in the nonaged case to ∼1.4 V in the aged case. Furthermore, the device using an aged SnCl2 solution also exhibits a much better long-term stability than that made of the fresh solution. These achievements in dopant/additive-free CsPbI2Br solar cells can be useful for future research on CsPbI2Br and tandem solar cells.

Enhancing Built‐In Electric Field and Defect Passivation through Gradient Doping in Inverted CsPbI2Br Perovskite Solar Cells

“…To date, champion PCEs of 17.03% and 15.92% have been achieved for n–i–p‐type (normal) and p–i–n (inverted)‐type PeSCs, respectively, both based on CsPbI 2 Br. [ 12–18 ] Nevertheless, such PCE values are still lower than those of hybrid PeSCs. Further improvement is highly demanded for all‐inorganic PeSCs.…”

“…It has been well recognized that solution‐processed inorganic PVK films, especially those prepared at a low temperature, are highly defective, [ 19 ] which usually result in large energy loss in PeSCs. For example, the highest reported open‐circuit voltages ( V OC ) are 1.40 and 1.27 V for normal and inverted CsPbI 2 Br PeSCs, [ 15,16 ] respectively, both much lower than the E g (≈1.9 eV) of PVK. Such large energy loss might be attributed to the severe defect‐induced nonradiative recombination.…”

Recombination junctions for efficient monolithic perovskite-based tandem solar cells: physical principles, properties, processing and prospects

“…The perovskite absorbers used for the most efficient tandem devices have a bandgap in between 1.63-1.70 eV. 35,49,56 Arguably, any 'highquality' PSC should have a V OC deficit (defined as E g /q À V OC ) of o0.4 V, 10,52,82 implying that well-performing perovskites with a 1.64 eV bandgap should deliver on the device level a V OC of B1.24 V. When this is combined with a spectrally-filtered SHJ bottom cell's V OC of B0.7 V, 49 achieving tandem V OC values 41.9 V is a reasonable target. However, as shown in Fig.…”

Structural Properties and Stability of Inorganic CsPbI3 Perovskites

“…In this regard, additive engineering, interface engineering, and charge transfer layer (CTL) modifications are commonly studied and optimized. [ 35–43 ]…”