Ultrafast self-trapping of photoexcited carriers sets the upper limit on antimony trisulfide photovoltaic devices

Abstract

Antimony trisulfide (Sb2S3) is considered to be a promising photovoltaic material; however, the performance is yet to be satisfactory. Poor power conversion efficiency and large open circuit voltage loss have been usually ascribed to interface and bulk extrinsic defects By performing a spectroscopy study on Sb2S3 polycrystalline films and single crystal, we show commonly existed characteristics including redshifted photoluminescence with 0.6 eV Stokes shift, and a few picosecond carrier trapping without saturation at carrier density as high as approximately 1020 cm−3. These features, together with polarized trap emission from Sb2S3 single crystal, strongly suggest that photoexcited carriers in Sb2S3 are intrinsically self-trapped by lattice deformation, instead of by extrinsic defects. The proposed self-trapping explains spectroscopic results and rationalizes the large open circuit voltage loss and near-unity carrier collection efficiency in Sb2S3 thin film solar cells. Self-trapping sets the upper limit on maximum open circuit voltage (approximately 0.8 V) and thus power conversion efficiency (approximately 16 %) for Sb2S3 solar cells.

ZnS Ultrathin Interfacial Layers for Optimizing Carrier Management in Sb2S3-based Photovoltaics

“…For Sb 2 S 3 solar cells without ZnS and with 2 cycles the reverse transfer lifetimes are 0.30 and 0.26 ns, respectively, being in line with literature values of cells utilizing TiO 2 substrates. 11 , 13 , 14 The trend of these charge recombination lifetimes obtained from TA spectroscopy ( Figure 8 ) with increasing ZnS thickness is mirrored by the macroscopic parameters that define the performance of the solar cells, in particular the V oc trends ( Figure 8 ), as predicted by theoretical models.. 10 The former mentioned beneficial effects of the ZnS interlayer, namely passivation and prevention of reverse electron transfer, and the converse, deleterious effect, namely prevention of forward transfer, also appear in impedance spectroscopy collected under real photovoltaic working conditions ( Figure 5 ).…”

“… 10 To date, the achievable efficiencies of antimony chalcogenides solar cells are largely held back by an open circuit voltage ( V oc ) deficit of ∼0.5–0.6 eV, for which self-trapped photoexcited carriers, defects in the bulk, and interfacial trap states have been considered as causes. 3 , 10 , 11 Insight into the dynamics of charge carriers in these systems has been provided by impedance spectroscopy and ultrafast optical methods, which allow one to cover time scales ranging from femtoseconds to seconds. 6 , 11 − 14 Ultrafast self-trapping of excitons in antimony chalcogenides, and in particular of Sb 2 S 3 , has been ascribed to the partly one-dimensional nature of the crystal and would set an intrinsic limitation for this family of materials.…”

“…3 , 10 , 11 Insight into the dynamics of charge carriers in these systems has been provided by impedance spectroscopy and ultrafast optical methods, which allow one to cover time scales ranging from femtoseconds to seconds. 6 , 11 − 14 Ultrafast self-trapping of excitons in antimony chalcogenides, and in particular of Sb 2 S 3 , has been ascribed to the partly one-dimensional nature of the crystal and would set an intrinsic limitation for this family of materials. 6 , 15 , 16 A completely distinct effect, however, has been pointed out as the dominant limitation, namely the recombination of photogenerated carriers at interface traps.…”

Experimental disclosing the composition- and structure-dependent deep-level defect in photovoltaic antimony trisulfide materials

“…Strikingly, there appear two photo-induced absorption peaks near 545 and 690 nm, both of which are assigned to a single broad feature of trapped carrier in Sb2S3. Especially, the peak at 690 nm is associated with the formation of sulfide radical 22,23 . Thus, the enhanced absorption at 690 nm for S-rich Sb2S3 could be attributed to abundant sulfide radical.…”

A photoanode with plasmonic nanoparticles of earth abundant bismuth for photoelectrochemical reactions

“…19 Along with the natural abundance of Sb 2 S 3 and the large optical absorption coefficient, the high stability and narrow bandgap (1.7-1.8 eV) make it a promising co-sensitizer of TiO 2 . [20][21][22][23][24][25] Liu et al, used a WO 3 /Sb 2 S 3 heterojunction electrode and obtained four-fold enhancement of photocurrent density (1.79 mA cm À2 at 0.8 V) over pristine WO 3 . 26 Also, Song et al reported a current density of 0.79 mA cm À2 at an onset of À0.08 V for TiO 2 /Sb 2 S 3 , while pristine TiO 2 shows poor performance under similar experimental conditions.…”