  In this article, we theoretically demonstrate multilevel impurity
photovoltaic effect in an efficient silicon dual-homojunction solar cell that
ensures an extended absorption of longer wavelength light. Along with suitable
contact work functions (Ni and Ta as anode and cathode, respectively), three
impurity energy levels from acceptor type impurities (One from Tl and two from
Zn) have been introduced in the energy gap of the absorber layer in the solar
cell. The pristine Si solar cell shows a PCE of 25.4% with JSC= 37.99 mA/cm2,
VOC=0.780V and FF=85.76%, respectively. The incorporation of Tl impurity level
alone provides a PCE of 33.4%, with JSC= 51.56 mA/cm2, VOC=0.789 V and
FF=82.03%, respectively. The PCE of the solar cell further enhances to 35.4%
with a further enhancement of the short circuit current by 3.76 mA/cm2 due to
the inclusion of Zn impurity into the optimized structure. This enhancement of
the JSC and hence PCE is resulted from the longer wavelength light absorption
due to impurity-assisted two-step photon upconversion in the solar cell.
