Semi-transparent a-Si:H p–i–n solar cells for dual purpose of screening and energy harvesting: a comparative study of simulation and experiment
摘要
There is emerging interest in developing semi-transparent solar cells that can be integrated into windows/glass panels in buildings to enable small-scale energy harvesting and screening/lighting of the rooms. However, the major challenge is to balance the power conversion efficiency (PCE) and average visible transmittance (AVT), which together define light utilisation efficiency (LUE). If such cells can also be fabricated at low temperatures, it further adds to the cause. Hydrogenated amorphous silicon (a-Si:H) which can be deposited at low temperature have been considered for this work. With this motivation, this work presents design and simulation of p–i–n junction solar cell comprising Ag/ITO/a-Si:H(p)/a-Si:H(i)/a-Si:H(n)/ITO and FTO /Glass substrate using TCAD-Sentaurus. The donor doping concentration (Nd) in a-Si:H(n) was varied from 1016 cm−3 to 1019 cm−3 to improve PCE. A maximum PCE of 7.75%, AVT of 11.69% and LUE 0.90% was achieved for Nd = 1019 cm−3. Subsequently, the a-Si:H(i) layer thickness was varied (100 nm, 80 nm, 60 nm and 40 nm) to improve AVT and LUE. For thickness range 40–80 nm showed AVT 15–25% and LUE ≥ 1% while keeping a reasonable PCE ≥ 4.89%. Later, the solar cells were fabricated using RF-PCEVD and RF- Sputtering to experimentally verify the simulations for a-Si:H(i) layer thickness range 40–80 nm. Results showed AVT 23–39% and LUE 0.87–1.16% with a reasonable PCE of 3–4%. Other parameters showed similar trends as observed in simulation. To investigate the mismatch in simulation and experiment, a series of simulation were performed for cell with 80 nm a-Si:H(i) layer with systemic introduction of defect densities and contact resistances. The observations showed a good match between experimental PCE = 3.70 ± 0.53% and simulation PCE = 4.03%.