Complete microcrystalline p-i-n solar cell—Crystalline or amorphous cell behavior?

Abstract

Complete μc-Si:H p-i-n solar cells have been prepared by the very high frequency glow discharge method. Up to now, intrinsic μc-Si:H has never attracted much attention as a photovoltaic active material. However, an efficiency of 4.6% and remarkably high short circuit current densities of up to 21.9 mA/cm2 due to an enhanced absorption in the near-infrared could be obtained. First light-soaking experiments indicate no degradation for the entirely μc-Si:H cells. Voltage-dependent spectral response measurements suggest that the carrier transport in complete μc-Si:H p-i-n cells may possibly be cosupported by diffusion (in addition to drift).

Some controversial points related to transport in microcrystalline silicon

“…For example, a great advantage of µc-Si:H is its stability against light soaking, important for the use in photovoltaic solar cells [1]. Both a-Si:H and µc-Si:H can be prepared by plasma enhanced chemical vapor deposition (PE CVD) and the a-Si:H / µc-Si:H transition can be achieved just by a change of any of the deposition parameters like substrate temperature (T S ), discharge frequency or hydrogen dilution (r H = [H 2 ] / [SiH 4 ]).…”

Controlling the quality of nanocrystalline silicon made by hot-wire chemical vapor deposition by using a reverse H2 profiling technique

“…Hydrogenated nanocrystalline silicon (nc-Si:H) has been intensively studied for photovoltaic applications because of its better stability against prolonged illumination than amorphous silicon (a-Si:H) and amorphous silicon germanium (a-SiGe:H) [1][2][3]. The conventional techniques of producing such material are based on plasma enhanced chemical vapor deposition (PECVD), and much research is dedicated to optimizing the plasma conditions for highrate deposition.…”

From amorphous to microcrystalline silicon: Moving from one to the other by halogenated silicon plasma chemistry

“…Those studies led, about ten years later, to µc-Si/a-Si:H p-n junction solar cells with improved properties [11,12]. In 1994, the preparation of a fully microcrystalline (µc-Si:H) silicon pi-n single-junction solar cell with new striking advantages compared to amorphous silicon (a-Si:H) was achieved [13].The main reason driving the transition from a-Si to µc-Si:H was the fact that the latter showed no light induced degradation unlike a-Si:H. Because of the favorable combination of the improved photostability, higher carrier mobility and lower optical absorption, µc-Si films are being used not only for solar cells but also as carrier injection layers in thin film transistors.…”