High-Performance Crystalline Si Solar Cell on n-Type Si With a Thin Emitter by Al-Induced Crystallization and Doping

A novel crystalline Si solar cell on n-type Si with a very thin emitter (35-nm thick), formed by Al-induced crystallization (AIC) and doping of an initially amorphous Si (a-Si) layer, is reported. The process for the emitter formation started with the deposition of an Al (10 nm)/a-Si (35 nm) bilayer on n-type Si, followed by annealing at 500°C. During annealing, the a-Si layer was crystallized and doped with Al; crystallization and doping depend on the process conditions and initial layers' thickness. With the specific conditions used, part of the a-Si layer remained amorphous (layer between the emitter and the Si substrate), and this was advantageous for solar cell operation. High-resolution transmission electron microscopy (TEM) was used to investigate the structural properties of the AIC layer. Grains within the crystallized layer showed preferred orientation in the (111) crystallographic direction. The fabricated solar cell with the above AIC thin emitter showed a power efficiency of 13.5% without using any antireflection coating or passivation layer. A special architecture was used at the front side of the solar cell, with the AIC layer developed on a thermal silicon oxide grid. The developed process is trending toward a simple, low-cost, low-temperature, high-efficiency c-Si solar cell.