Pre-deposited alkali (Li, Na, K) chlorides layer for effective doping of CuInSSe thin films as absorber layer in solar cells

We introduce an effective method for copper indium sulfide selenide (CISSe) doping with different alkali metals (Li, Na and K) based on a pre-deposited alkali chloride layer. A simple and fast spray method is used for pre-deposition of alkali chloride layer (LiCl, NaCl, KCl) on substrate surface before spray pyrolysis deposition of copper indium disulfide CuInS2 (CIS) films followed by selenization. The different properties of alkali-doped CISSe films by the alkali chloride pre-deposition (ACPD) method were compared to the post-deposition treatment (PDT) method. Based on FESEM images, a highly compact film with large grains can be obtained for CISSe films doped with K(similar to 0.72 mu m) and Na (similar to 0.56 mu m) by the ACPD method that is considerably higher than undoped films (similar to 0.47 mu m). While for the PDT method, grain size decreased after the doping process. UV-Vis analysis showed that alkali atoms with larger size result in more band gap widening of CISSe film. According to Mott-Schottky results, all films are p-type but doping density is dependent on the doping method. CISSe films doped by the ACPD method show smaller doping density, the smallest value of carrier concentration is 3.1 x 10(17) cm(-3) for K-doped CISSe film. All CISSe doped films by ACPD method show higher mobility compared to CISSe film doped by PDT method and larger atom results in higher mobility. The numerical modeling work using SCAPS software showed that solar device with ACPD K-doped CISSe film as absorber layer results in higher efficiency compared to Li, Na- doped and undoped CISSe films.

Automated summary

We introduce an effective method for doping copper indium sulfide selenide (CISSe) with different alkali metals by pre-depositing an alkali chloride layer. The alkali chloride layer is sprayed onto the substrate surface before spray pyrolysis deposition of copper indium disulfide (CIS) films and selenization. The alkali-doped CISSe films prepared by the pre-deposition method show improved film compactness and larger grain size compared to undoped films. The alkali atoms with larger size result in wider band gap of CISSe film.