Abstract
Solar cells with a short-circuit current density ( J sc ) of 6 mA/cm 2, an open circuit voltage ( V oc ) of 280 mV and a conversion efficiency of 0.5% under a 1000 W/m 2 solar radiation were prepared by sequential chemical deposition of Bi 2S 2 (160 nm) and PbS (400 nm) thin films. The optical band gap ( E g ) of Bi 2S 3 (160 nm) decreased from 1.67 to 1.61 eV upon heating the as-deposited film at 250 °C in air for 15 min to make it crystalline, but also reduced its thickness to 100 nm. Photoconductivity of this film is 0.003 (Ω cm) − 1 . The E g of PbS film (200 nm) deposited at 25 °C (24 h) is 0.57 eV, and is 0.49 eV for the film deposited at 40 °C. The electrical conductivity of the latter is 0.48 (Ω cm) − 1 . The photo-generated current density for a Bi 2S 3(100 nm)/PbS(300 nm) absorber stack is above 40 mA/cm 2 under AM 1.5 G (1000 W/m 2) solar radiation. However, the optical losses in the cell structure reduces the J sc . Spectral sensitivity of the external quantum efficiency of the cell establishes the contribution of Bi 2S 3 and PbS to J sc . The energy level diagram of the cell structure suggests a built-in potential of 470 mV for the present case. Six series-connected cells gave the V oc of 1.4 V and J sc of 5 mA/cm 2.
Published Version
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