Bandgap engineering of ZnSnP2 for high-efficiency solar cells

Abstract

ZnSnP2, an absorber material for solar cells, transitions from an ordered chalcopyrite to a disordered sphalerite structure at high temperatures. We investigate the electronic structure of both phases, combining a screened hybrid density functional with the special quasi-random structure method. We predict a bandgap reduction of 0.95 eV between the ordered and fully disordered materials. Experimental reports are consistent with partial disorder. Tuning of the order parameter would lead to a family of ZnSnP2 phases with bandgaps ranging from 0.75 eV to 1.70 eV, thus providing graded solar cell absorbers from a single material system.

Enhancing the efficiency of SnS solar cells via band-offset engineering with a zinc oxysulfide buffer layer

“…1 Tin(II) sulfide (SnS) is among the ongoing investigated materials such as Cu 2 O, 2 Cu 2 S, 3 FeS 2 , 4,5 Cu 2 ZnSn(S x Se 1-x ) 4 , 6 and ZnSnP 2 . 7 SnS has a suitable bandgap (E g ~ 1.1 -1.5 eV), 8,9 strong optical absorption (α > 10 4 cm -1 ), 10 and proper carrier concentration ([p] ~ 10 14 -10 17 cm -3 ). 11 Recently, a record efficiency SnS solar cell of 1.95% (active area) was fabricated from p-n homojunction nanowires using boron and phosphorus as dopants.…”

Quasi-particle electronic band structure and alignment of the V-VI-VII semiconductors SbSI, SbSBr, and SbSeI for solar cells

“…One potential issue arises where species with similar size and co-ordination preferences are present in the same material, which can lead to the formation of anti-site defects in high concentrations. Cation disorder has been observed in systems ranging from ZnSnP 2 2,3 to Cu 2 ZnSnS 4 4,5 and is typically associated with poor photovoltaic performance (low open-circuit voltages resulting from high electronhole recombination rates). 6,7 V-VI-VII semiconductors are interesting chemically as they are ternary materials, usually formed of a trivalent cation with divalent and monovalent anions.…”

Origin of the failed ensemble average rule for the band gaps of disordered nonisovalent semiconductor alloys

“…For the direct-band-gap isovalent alloys, it was found E g (CH) > E g (CA) > E g (CP) 16 , where CH, CA, and CP represent the ordered chalcopyrite, CuAu-, and CuPt-like structures respectively, and the random alloy has a band gap close to the ensemble averaged value of these ordered ones. However, for the nonisovalent alloys, the band gap of the random structure could be very small, and even smaller than that of the CP structure 9 . Nevertheless, such a small band gap has never been observed experimentally.…”

“…However, for the nonisovalent alloys, the compositions can only exist around some discrete values, to satisfy the charge neutrality rule. For example, the Zn x Sn y P, which has recently been proposed as a promising candidate for solar cells [7][8][9] , exists only in a small range around x = y = 0.5; the Cu x In y Se, which is widely used for thinfilm solar cells 10,11 , can also exist at other compositions besides x = y = 0.5, such as CuIn 3 Se 5 . The properties of the isovalent alloys have been extensively studied.…”