Stepwise tuning of the doping and thickness of a-Si:H(p) emitter layer to improve the performance of c-Si(n)/a-Si:H(p) heterojunction solar cells

Abstract

Crystalline silicon (c-Si)/ hydrogenated amorphous silicon (a-Si:H) heterojunction (Ag/Al/c-Si(n)/a-Si:H(i)/a-Si:H(p)/ITO/Ag) solar cells were fabricated by RF-PECVD technique. The efficiency (η), short circuit current density (Jsc) and fill factor (FF) of the heterojunction (HJ) solar cells were improved from 10 to 17%, 24 to 32 mA/cm2 and 0.60 to 0.74 respectively through systematic tuning of processing steps; the thickness and doping of a-Si:H(p) layer respectively. High open circuit voltage (Voc) of 705 mV could be achieved by improving the interfaces between the a-Si:H layers and c-Si by inserting an ultrathin intrinsic a-Si:H film using H2 plasma treatment on c-Si(n) wafer and a-Si:H(i) layer respectively. Simultaneously, other solar parameters like Jsc and FF were also improved step by step by carefully adjusting the gas flow rate and deposition time of doped a-Si:H(p) layer. By increasing the doping of a-Si:H(p) layer, electric field at the interface could be enhanced, which led to the immediate separation of electron–hole pair and thus improving the solar cell parameters. This is also confirmed by external quantum efficiency (EQE) spectra measured with and without external reverse bias.