Vacuum-Free, Room-Temperature Organic Passivation of Silicon: Toward Very Low Recombination of Micro-/Nanotextured Surface Structures

Crystalline silicon (c-Si) solar cells remain dominant in the photovoltaic (PV) market because of their cost-effective advantages. However, the requirement for expensive vacuum equipment and the power-hungry thermal budget for surface passivation technology, which is one of the key enablers of the high performance of c-Si solar cells, impede further reductions of costs. Thus, the omission of the vacuum and high-temperature process without compromising the passivation effect is highly desirable due to cost concerns. Here, we demonstrate a vacuum-free, room-temperature organic Nafion thin-film passivation scheme with an effective minority carrier lifetime (pi(eff)) exceeding 9 ms on an n-type c-Si wafer with a resistivity of 1-5 Omega.cm, corresponding to an implied open circuit voltage (iV(oc)) of 724 mV and upper-limit surface recombination velocity (SRV) of 1.46 cm/s, which is a level that is in line with the hydrogenated amorphous Si film-passivation scheme used in the current PV industry. We find that the Nafion film passivation of Si can be enhanced in an O-2 atmosphere and that the Nafion/c-Si interface oxidation should be responsible for the passivation mechanism. This highly effective passivation is also achieved on various micro-/nanotextured Si surface structures from actual production, including a pyramidal surface and nanopore-pyramid hybrid structure with nanopores on the inclined plane of the pyramid. We develop an organic Nafion-passivated n-type back-junction Si solar cell to examine application in a real device. The open circuit voltage (V-oc) of the solar cell with the Nafion passivation layer achieves a clear improvement (30.8 mV) over those without the passivation layer, resulting in an increase (1.5%) in the power conversion efficiency. These results suggest the potential use of these organic electronics with current Si microelectronics and a new strategy for the development of vacuum-free, low-temperature Si-based PVs at low cost.