Aluminum-oxide-based inversion layer solar cells on n-type crystalline silicon: Fundamental properties and efficiency potential

We introduce a rear-emitter inversion layer (IL) solar cell on n-type crystalline silicon (n-Si). The hole IL is induced by the high density of negative fixed charges in an aluminum oxide (Al₂O₃) surface passivation layer. For the formation of contacts to the inversion layer, we employ a single-step p⁺ laser doping process, using aluminum from the Al₂O₃ layer as dopant source. Lateral hole transport through the IL underneath the n-Si/Al₂O₃ interface is analyzed by electrical measurements. The IL hole mobility is shown to be only marginally reduced by scattering at the high density of fixed charges at the n-Si/Al₂O₃ interface, resulting in an inversion layer sheet resistance of 15–18 kΩ/sq (in the dark). The effective sheet resistance of the IL is shown to decrease to below 4 kΩ/sq under solar cell operating conditions. Based on two-dimensional device simulations, we show that the proposed type of n-type silicon IL solar cell has a very high efficiency potential exceeding 26% including contact recombination losses.