• Energy Research

Abstract A novel dopant-free ZnS/p-Si heterojunction solar cell with WO3 thin films as hole-selective contact was fabricated using thermal evaporation method. The obtained maximum power conversion efficiency (PCE) of 10.94% is the highest recorded value for ZnS/p-Si heterojunction solar cells, to the best of our knowledge. The transfer line matrix (TLM) measurements indicate that the contact between WO3 thin films and p-Si is ohmic behavior, with a contact resistivity (ρc) of 12.7 mΩ cm2. The forming mechanism of the ohmic contact behavior between WO3 thin films and p-Si was explained from the aspect of energy band. A power-loss analysis based on the ZnS/p-Si heterojunction solar cell was carried out for the first time. The results reveal that shading loss, NIR parasitic absorption, and base collection loss occupy the main optical loss pathways, while the bulk resistance of the undoped ZnS thin films and the finger contact resistivity are the most limiting series-resistance components. Minority-carrier lifetime measurments of p-Si, which was passivated with polystyrenesulfonate (PSS) thin films, indicate that the poor quality of p-Si is likely responsible for the shunt-resistance loss. Based on the power-loss analysis, several optimization strategies are proposed.

Abstract A novel dopant-free ZnS/p-Si heterojunction solar cell with WO3 thin films as hole-selective contact was fabricated using thermal evaporation method. The obtained maximum power conversion efficiency (PCE) of 10.94% is the highest recorded value for ZnS/p-Si heterojunction solar cells, to the best of our knowledge. The transfer line matrix (TLM) measurements indicate that the contact between WO3 thin films and p-Si is ohmic behavior, with a contact resistivity (ρc) of 12.7 mΩ cm2. The forming mechanism of the ohmic contact behavior between WO3 thin films and p-Si was explained from the aspect of energy band. A power-loss analysis based on the ZnS/p-Si heterojunction solar cell was carried out for the first time. The results reveal that shading loss, NIR parasitic absorption, and base collection loss occupy the main optical loss pathways, while the bulk resistance of the undoped ZnS thin films and the finger contact resistivity are the most limiting series-resistance components. Minority-carrier lifetime measurments of p-Si, which was passivated with polystyrenesulfonate (PSS) thin films, indicate that the poor quality of p-Si is likely responsible for the shunt-resistance loss. Based on the power-loss analysis, several optimization strategies are proposed.

In order to investigate the light-induced-degradation (LID) and regeneration of industrial PERC solar cells made from different positions of silicon wafers in a silicon ingot, five groups of silicon wafers were cut from a commercial solar-grade boron-doped Czochralski silicon (Cz-Si) ingot from top to bottom with a certain distance and made into PERC solar cells by using the standard industrial process after measuring lifetimes of minority carriers and concentrations of boron, oxygen, carbon, and transition metal impurities. Then, the changes of their I - V characteristic parameters (efficiency η , open-circuit voltage V oc , short-circuit current I sc , and fill factor FF ) with time were in situ measured by using a solar cell I - V tester during the 1st LID (45°C, 1 sun, 12 h), regeneration (100°C, 1 sun, 24 h), and 2nd LID (45°C, 1 sun, 12 h). The results show that the LID and regeneration of the PERC solar cells are caused by the transition of B-O defects playing a dominant role together with the dissociation of Fe-B pairs playing a secondary role. The decay of η during the 1st LID is caused by the degradation of V oc , I sc , and FF , while the increase of η during the regeneration is mainly contributed by V oc and FF , and the decay of η during the 2nd LID is mainly induced by the degradation of I sc . After regeneration, the decay rate of η reduces from 4.43%–5.56% (relative) during the 1st LID to 0.33%–1.75% (relative) during the 2nd LID.

In order to investigate the light-induced-degradation (LID) and regeneration of industrial PERC solar cells made from different positions of silicon wafers in a silicon ingot, five groups of silicon wafers were cut from a commercial solar-grade boron-doped Czochralski silicon (Cz-Si) ingot from top to bottom with a certain distance and made into PERC solar cells by using the standard industrial process after measuring lifetimes of minority carriers and concentrations of boron, oxygen, carbon, and transition metal impurities. Then, the changes of their I - V characteristic parameters (efficiency η , open-circuit voltage V oc , short-circuit current I sc , and fill factor FF ) with time were in situ measured by using a solar cell I - V tester during the 1st LID (45°C, 1 sun, 12 h), regeneration (100°C, 1 sun, 24 h), and 2nd LID (45°C, 1 sun, 12 h). The results show that the LID and regeneration of the PERC solar cells are caused by the transition of B-O defects playing a dominant role together with the dissociation of Fe-B pairs playing a secondary role. The decay of η during the 1st LID is caused by the degradation of V oc , I sc , and FF , while the increase of η during the regeneration is mainly contributed by V oc and FF , and the decay of η during the 2nd LID is mainly induced by the degradation of I sc . After regeneration, the decay rate of η reduces from 4.43%–5.56% (relative) during the 1st LID to 0.33%–1.75% (relative) during the 2nd LID.

AbstractIn this work, we propose a route to achieve a certified efficiency of up to 24.51% for silicon heterojunction (SHJ) solar cell on a full‐size n‐type M2 monocrystalline‐silicon Cz wafer (total area, 244.53 cm2) by mainly improving the design of the hydrogenated intrinsic amorphous silicon (a‐Si:H) on the rear side of the solar cell and the back reflector. A dense second intrinsic a‐Si:H layer with an optimized thickness can improve the vertical carrier transport, resulting in an improved fill factor (FF). In order to reduce the plasmonic absorption at the back reflector, a low‐refractive‐index magnesium fluoride (MgF2) is deposited before the Ag layer; this leads to an improved gain of short circuit current density (Jsc). In total, together with MgF2 double antireflection coating and other fine optimizations during cell fabrication process, ~1% absolute efficiency enhancement is finally obtained. A detailed loss analysis based on Quokka3 simulation is presented to confirm the design principles, which also gives an outlook of how to improve the efficiency further.

AbstractIn this work, we propose a route to achieve a certified efficiency of up to 24.51% for silicon heterojunction (SHJ) solar cell on a full‐size n‐type M2 monocrystalline‐silicon Cz wafer (total area, 244.53 cm2) by mainly improving the design of the hydrogenated intrinsic amorphous silicon (a‐Si:H) on the rear side of the solar cell and the back reflector. A dense second intrinsic a‐Si:H layer with an optimized thickness can improve the vertical carrier transport, resulting in an improved fill factor (FF). In order to reduce the plasmonic absorption at the back reflector, a low‐refractive‐index magnesium fluoride (MgF2) is deposited before the Ag layer; this leads to an improved gain of short circuit current density (Jsc). In total, together with MgF2 double antireflection coating and other fine optimizations during cell fabrication process, ~1% absolute efficiency enhancement is finally obtained. A detailed loss analysis based on Quokka3 simulation is presented to confirm the design principles, which also gives an outlook of how to improve the efficiency further.