Extremely low surface recombination in 1 Ω cm n‐type monocrystalline silicon

Abstract

A key requirement in the recent development of highly efficient silicon solar cells is the outstanding passivation of their surfaces. In this work, plasma enhanced chemical vapour deposition of a triple layer dielectric consisting of amorphous silicon, silicon oxide and silicon nitride, charged extrinsically using corona, has been used to demonstrate extremely low surface recombination. Assuming Richter's parametrisation for bulk lifetime, an effective surface recombination velocity Seff = 0.1 cm/s at Δn = 1015 cm–3 has been obtained for planar, float zone, n -type, 1 Ω cm silicon. This equates to a saturation current density J0s = 0.3 fA/cm2, and a 1-sun implied open-circuit voltage of 738 mV. These surface recombination parameters are among the lowest reported for 1 Ω cm c-Si. A combination of impedance spectroscopy and corona-lifetime measurements shows that the outstanding chemical passivation is due to the small hole capture cross section for states at the interface between the Si and a-Si layer which are hydrogenated during nitride deposition

Temporary Surface Passivation for Characterisation of Bulk Defects in Silicon: A Review

“…HF passivation also gives excellent passivation in n‐type silicon, however lower S have been reported using thin films (see Section 4.4). Compared to the best dielectric passivation films to date, HF passivation has demonstrated equivalent passivation levels, which is astonishing considering the basic principles of the technique.…”

“…Charge modification (e.g., by corona charging) can be used to improve the properties of as‐deposited dielectrics. Even better passivation can be achieved with stacks of materials …”

“…Even better passivation can be achieved with stacks of materials. [12,13] Whilst improvements in passivation have resulted in better photovoltaic devices, use of state-of-the art passivation processes can cause confusion when trying to understand defect physics and the true bulk lifetime in device process development. The starting bulk lifetime can change (positively or negatively depending on details) during the passivation process, both due to defect re-configuration and because the wafer bulk is not a closed system.…”

Superacid-Treated Silicon Surfaces: Extending the Limit of Carrier Lifetime for Photovoltaic Applications

“…Specifically, hydrogen-rich silicon nitride (SiN x :H) [4], aluminum oxide (Al 2 O 3 ) [5], and amorphous silicon (a-Si:H) [6] have all demonstrated surface recombination velocities (S) of < 1 cm/s, with additional corona charging giving S as low as 0.1 cm/s in some cases [7]. It is, therefore, no surprise that a record efficiency of 26.6% [8] has been achieved by utilizing vacuum-deposited a-Si:H films for exceptional surface passivation, which in contrast to thermal oxidations, also retain very long carrier diffusion lengths during cell fabrication, owing to the low processing temperatures for this cell architecture (< 300°C).…”

Controlling Surface Carrier Density via a PEDOT:PSS Gate: An Application to the Study of Silicon‐Dielectric Interface Recombination

“…PECVD amorphous silicon (a‐Si) using silane and hydrogen as precursors . PECVD silicon oxide (SiO x ) using silane and nitrous oxide as precursors . And last, plasma‐assisted atomic layer deposited (PA‐ALD) aluminum oxide using a Oxford Instruments OpAL reactor .…”