Simulation Study On The Interface Photoelectric Properties And Device Performance Of CdMnTe Film Solar Cell

Cadmium manganese telluride（CdMnTe）film is considered as an ideal top-layer solar cell material due to its excellent optical properties,good chemical stability,high electronic transmission performance and continuous tunable band gap between 1.45e V and 2.85e V.The typical CdMnTe film solar cells usually adopt the upper configuration structure,which is composed of glass,front electrode,CdS window layer,CdMnTe absorption layer,back contact layer and back electrode.It is found that the interface states at the CdS/CdMnTe interface due to the destruction of atomic periodic arrangement would capture the photogenerated carriers and reduce the performance of solar cell.In order to overcome the short wavelength effect of CdS in CdMnTe film solar cells,the thickness of the window layer can be appropriately reduced and the high-resistance transparent（HRT）TiO₂ buffer layer can be inserted between the window layer and the front electrode to form a composite window layer,which can increase the light utilization rate and improve the photoelectric conversion efficiency.In this study,the CdS/CdMnTe interface states and optical properties of TiO₂/CdS composite window layer are systematically investigated by first principles calculations.In addition,the numberial simulation method is used to study the CdMnTe film solar cells.Firstly,the first priciples method is used to calculate the lattice structure and photoelectric properties of CdS（002）,CdMnTe（111）surface and the CdS/CdMnTe interface.Two CdS/CdMnTe interface models with different positions of Mn atom have been established,and the CdS/CdMnTe interface with Mn atoms in the middle layer is more stable,which interface binding energy is-0.53J/m².The density of states shows that there is no interface state near the Fermi level in CdS/CdMnTe interface.Besides,the atoms of CdS/CdMnTe interface have hybridizations and charge transfer,which can enhance the interface bonding.Secondly,the lattice structure and photoelectric properties of bulk CdS,TiO₂,TiO₂（110）surface and TiO₂/CdS interface are stuied by first principles method.The results show that for the incident light with wavelength range of 100-200nm,the transmittance of CdS is about 5%,while for the incident light with wavelength range of 200-520nm,the transmittance of CdS increases gradually,but the overall transmittance is small.Compared with bulk CdS,the bulk TiO₂ mainly absorbs ultraviolet light and hardly absorbs incident light with wavelength greater than 350nm,which can be used as HRT layer material for CdMnTe film solar cells.The TiO₂/CdS interface structure which formed by the CdS（002）diatomic termination surface and TiO₂（110）surface is more stable,and its interface binding energy is-0.87J/m².The TiO₂/CdS composite window layer has a transmittance of 70%in the wavelength range of300-520nm,and its absorption coefficient is also low,which can make more photons reach the absorption layer and improve the solar cell performance.Last,the influence of the thickness of CdS window layer and TiO₂ HRT layer on the performance of CdMnTe film solar cells was simulated by wx AMPS.The results show that the conversion efficiency of CdMnTe solar cells are significantly improved with the decrease of the thickness of CdS window layer,indicating that the CdMnTe solar cell performance could be effectively improved by appropriately reducing the thickness of CdS window layer.After adding HRT layer TiO₂ to form a composite window layer,the photon utilization rate in the short-wave region is higher than that in the single window layer,and the J_sc and the conversion efficiency of the solar cell are also significantly improved.Therefore,TiO₂ can be used as HRT layer material in CdMnTe film solar cell,which helps to improve the short wavelength response and improve the conversion efficiency of CdMnTe film solar cell.