Plasma damage-free deposition of transparent Sn-doped In2O3 top cathode using isolated plasma soft deposition for perovskite solar cells

We developed an isolated plasma soft deposition (IPSD) technique for the plasma damage-free deposition of a Sn-doped In2O3 (ITO) top cathode on semi-transparent perovskite solar cells (PSCs). Unlike the directly faced plasma in conventional magnetron sputtering, the isolated plasma region in the IPSD process prevents the direct irradiation of plasma and facilitates plasma damage-free sputtering. Effective confinement of high-density plasma in isolated regions by using a specific Nd-Fe-B45 magnet array also prevents irradiation of energetic particles sputtered from faced ITO targets. In addition, linear scanning of the substrate in the isolated plasma region resulted in a low-temperature and large-area coating of the ITO top cathode without plasma damage for semi-transparent PSCs. Without intentional substrate heating, the IPSD-processed ITO film with a thickness of 100 nm under optimal conditions exhibited a low sheet resistance of 33.02 Ohm/square, high optical transmittance of 91.27%, root mean square roughness of 0.252 nm, and work function of 4.33 eV. To demonstrate the feasibility of IPSD, we fabricated PSCs with thermally evaporated perovskite active layers. Compared with the power conversion efficiency (PCE: 4.35%) of PSCs with magnetron-sputtered ITO cathode, the PSC with IPSD-processed ITO cathode exhibited a similar PCE (15.52%) because of the absence of plasma damage. Considering the commercialization of PSCs, the IPSD-based top cathode coating process possesses great potential as a key technique for bidirectional or semi-transparent PSCs.