TY - JOUR
T1 - Ultra-thin electron collectors based on nc-Si:H for high-efficiency silicon heterojunction solar cells
AU - Zhao, Yifeng
AU - Mazzarella, Luana
AU - Procel, Paul
AU - Han, Can
AU - Tichelaar, Frans D.
AU - Yang, Guangtao
AU - Weeber, Arthur
AU - Zeman, Miro
AU - Isabella, Olindo
PY - 2021
Y1 - 2021
N2 - Low parasitic absorption and high conductivity enable (n)-type hydrogenated nanocrystalline silicon [(n)nc-Si:H], eventually alloyed with oxygen [(n)nc-SiOx:H], to be deployed as window layer in high-efficiency silicon heterojunction (SHJ) solar cells. Besides the appropriate opto-electrical properties of these nanocrystalline films, reduction of their thickness is sought for minimizing parasitic absorption losses. Many strategies proposed so far reveal practical limits of the minimum (n)-layer thickness that we address and overcome in this manuscript. We demonstrated the successful application of an ultra-thin layer of only 3-nm-thick based on (n)nc-Si:H PECVD plasma growth conditions without the use of additional contact or buffer layers. For simplicity, we still name (n)nc-Si:H this ultra-thin layer and the solar cell endowed with it delivers a certified efficiency η of 22.20%. This cell shows a 0.61 mA/cm2 overall JSC gain over the (n)a-Si:H counterpart mainly owing to the higher transparency of (n)nc-Si:H, while maintaining comparable VOC > 714 mV and FF > 80%. Our optimized (n)nc-Si:H layer yields low absorption losses that are commonly measured for (n)nc-SiOx:H films. In this way, we are able to avoid the detrimental effect that oxygen incorporation has on the electrical parameters of these functional layers. Further, by applying a MgF2/ITO double-layer anti-reflection coating, a cell with 3-nm-thick (n)nc-Si:H exhibits a JSC,EQE up to 40.0 mA/cm2. By means of EDX elemental mapping, we additionally identified the (n)nc-Si:H/ITO interface as critical for electron transport due to unexpected oxidation. To avoid this interfacial oxidation, insertion of a 2-nm-thick (n)a-Si:H on the 3-nm-thick (n)nc-Si:H contributes to FF gains of 1.4%abs. (FF increased from 78.6% to 80.0%), and showing further room for improvements.
AB - Low parasitic absorption and high conductivity enable (n)-type hydrogenated nanocrystalline silicon [(n)nc-Si:H], eventually alloyed with oxygen [(n)nc-SiOx:H], to be deployed as window layer in high-efficiency silicon heterojunction (SHJ) solar cells. Besides the appropriate opto-electrical properties of these nanocrystalline films, reduction of their thickness is sought for minimizing parasitic absorption losses. Many strategies proposed so far reveal practical limits of the minimum (n)-layer thickness that we address and overcome in this manuscript. We demonstrated the successful application of an ultra-thin layer of only 3-nm-thick based on (n)nc-Si:H PECVD plasma growth conditions without the use of additional contact or buffer layers. For simplicity, we still name (n)nc-Si:H this ultra-thin layer and the solar cell endowed with it delivers a certified efficiency η of 22.20%. This cell shows a 0.61 mA/cm2 overall JSC gain over the (n)a-Si:H counterpart mainly owing to the higher transparency of (n)nc-Si:H, while maintaining comparable VOC > 714 mV and FF > 80%. Our optimized (n)nc-Si:H layer yields low absorption losses that are commonly measured for (n)nc-SiOx:H films. In this way, we are able to avoid the detrimental effect that oxygen incorporation has on the electrical parameters of these functional layers. Further, by applying a MgF2/ITO double-layer anti-reflection coating, a cell with 3-nm-thick (n)nc-Si:H exhibits a JSC,EQE up to 40.0 mA/cm2. By means of EDX elemental mapping, we additionally identified the (n)nc-Si:H/ITO interface as critical for electron transport due to unexpected oxidation. To avoid this interfacial oxidation, insertion of a 2-nm-thick (n)a-Si:H on the 3-nm-thick (n)nc-Si:H contributes to FF gains of 1.4%abs. (FF increased from 78.6% to 80.0%), and showing further room for improvements.
KW - (n)-type window layers
KW - hydrogenated nanocrystalline silicon
KW - hydrogenated nanocrystalline silicon oxide
KW - opto-electrical properties
KW - ultra-thin (n)-contact
UR - http://www.scopus.com/inward/record.url?scp=85119523438&partnerID=8YFLogxK
U2 - 10.1002/pip.3502
DO - 10.1002/pip.3502
M3 - Article
AN - SCOPUS:85119523438
SN - 1062-7995
VL - 30
SP - 809
EP - 822
JO - Progress in Photovoltaics: research and applications
JF - Progress in Photovoltaics: research and applications
IS - 8
ER -