Solar cells using bulk crystals of rare metal-free compound semiconductor ZnSnP2

Abstract

We report on current density–voltage (J–V) characteristics of solar cells using bulk crystals of ZnSnP2 obtained by solution growth, where Sn was used as a solvent. The minority carrier lifetimes of fast and slow components in bulk crystals of ZnSnP2 were 0.442 and 37.8 ns, respectively, which were obtained by analysis using double exponential function in time-resolved photoluminescence (TRPL) under the excitation power of 5.05 mW with the beam area of 0.5 mm2. The lifetime is close to that of CIGS, which is as high as to achieve the conversion efficiency of over 16%. TRPL also revealed that the recombination at the surface was dominant since the intensity of fast component was much larger than that of slow component. The well-known structure Al/Al-doped ZnO/ZnO/CdS/ZnSnP2/Mo was adopted for solar cells. The short-circuit current density and the open-circuit voltage are 1.99 mA cm−2 and 0.172 V, respectively. The wavelength at the absorption edge in external quantum efficiency is consistent with the bandgap of ZnSnP2. However, the conversion efficiency is 0.087%. The J–V curve suggests that the reduction of series resistance is required because it is higher than the value expected from the resistivity of bulk ZnSnP2. The improvement of conduction band offset is also necessary considering from our previous works.