An antibonding valence band maximum enables defect-tolerant and stable GeSe photovoltaics

Abstract

In lead–halide perovskites, antibonding states at the valence band maximum (VBM)—the result of Pb 6s-I 5p coupling—enable defect-tolerant properties; however, questions surrounding stability, and a reliance on lead, remain challenges for perovskite solar cells. Here, we report that binary GeSe has a perovskite-like antibonding VBM arising from Ge 4s-Se 4p coupling; and that it exhibits similarly shallow bulk defects combined with high stability. We find that the deep defect density in bulk GeSe is ~1012 cm−3. We devise therefore a surface passivation strategy, and find that the resulting GeSe solar cells achieve a certified power conversion efficiency of 5.2%, 3.7 times higher than the best previously-reported GeSe photovoltaics. Unencapsulated devices show no efficiency loss after 12 months of storage in ambient conditions; 1100 hours under maximum power point tracking; a total ultraviolet irradiation dosage of 15 kWh m−2; and 60 thermal cycles from −40 to 85 °C.

Ge 4s2 lone pairs and band alignments in GeS and GeSe for photovoltaics

“…Finally, Ge is in the 2+ oxidation state in both GeS and GeSe and adopts a distorted local structure, which suggests they may have stereochemically active lone pairs. [17][18][19] These properties, along with the recently reported 5.2% power conversion efficiency for a GeSe solar cell 20 , demonstrate the potential of these materials.…”

Raman Spectra of Bulk and Few-Layer GeSe From First-Principles Calculations

“…forms by an in-plane vibration along the armchair direction, indicating an intrinsic ferroelectric vibration mode in one layer of bulk GeSe, which agrees with previous experiment work (Zhao et al, 2018). Monolayer GeSe has been predicted a member of ferrovalley materials with plenty of fantastic physical properties (Morales-Ferreiro et al, 2017;Shen et al, 2018;Liu et al, 2021). Thus, it is necessary to investigate the Raman spectrum dependence of fewlayer.…”

Alternative Lone‐Pair ns2‐Cation‐Based Semiconductors beyond Lead Halide Perovskites for Optoelectronic Applications

“…[ 70 ] Hu's group did a series of studies on GeSe for PV application. [ 37,145–147 ] In particular, combined with theoretical and experimental analysis, they confirmed that the efficiency of PV device previously fabricated by CdS/GeSe heterojunction was predominantly limited by interfacial defects, rather than bulk defects in GeSe (Figure 6g). Then, they focused on the interfacial defect passivation by introducing Sb 2 Se 3 layer between GeSe and CdS, resulting in a record efficiency of 5.2% for GeSe‐based solar cells to date (Figure 6i).…”

“…Then, they focused on the interfacial defect passivation by introducing Sb 2 Se 3 layer between GeSe and CdS, resulting in a record efficiency of 5.2% for GeSe‐based solar cells to date (Figure 6i). [ 37 ] The device also exhibited excellent humidity and light stability. It was previously reported that a phototransistor fabricated by GeSe nanosheets can achieve a remarkable responsivity of ≈1.6 × 10 5 A W −1 .…”

“…[ 22,57,105 ] In order to inhibit the unfavorable factors, introducing passivation and optimizing the crystallization are effective methods to reduce carrier recombination and boost high‐quality products. [ 37,87 ] From the point view of device architecture, many approaches, including composition engineering, heterojunction establishment, nanostructure modulation, and suitable transporting layers selection, can also contribute to the performance enhancement. [ 4,6,55,98 ] Most of these efforts have been aimed at improving the performance related to the carrier transport, such as the power conversion efficiency, detectivity, sensitivity, and catalytic activity.…”