Description:TECHNICAL FIELD
[0001] The present disclosure relates generally to field of electrical and electronics device. More particularly, the present disclosure provides a CZTSSe based solar cell to increase power conversion efficiency with Sn2S3 layer.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] CZTSSe based solar cell structures have shown remarkable properties in terms of low cost, greater stability, high absorption coefficient and relatively inexpensive production process. However, maximum achieved values of power conversion efficiency (PCE) from the CZTSSe based solar cell structures hover close to 12.6 % only. Reason for low power conversionefficiencyis mainly due to problem of back surface recombination of carriers in the solar cell structures. Carriers generated inabsorber layer are free to move towardsbackwards or towards forward. Therefore, there is a probability that electrons will move towardsrear end of the solar cell structuresand recombine here without giving power toexternal circuit.
[0004] Existing materials used for increasing power efficiency of the solar cell structuresand can be used as Back surface field (BSF) like tin sulphide (SnS). However, SnS doesnot efficiently prevent carriers to recombine. Band atinterface of CZTSSe/SnS is towards downwards. So, there is chance that the set ofelectrons will move towards the solar cell structuresand recombine. Therefore, efficiency of SnS material is less. However, for appropriate functioning of solar cell, collection of generated charge is required. Andcollection is only possible if the set ofelectrons will move towardselectrodes present atfront end. So, there is need of layer that prevents the set of electrons to move towardsrear end.
[0005] There is a need to overcome above mentioned problems of prior art by bringing a solution that facilitates increasing power conversionefficiency of solar cell structures and reducing recombination of rear end of the solar cell structures and enables in enhancing collection of the set of carriers.

OBJECTS OF THE PRESENT DISCLOSURE
[0006] Some of the objects of the present disclosure, which at least one embodiment herein satisfies are as listed herein below.
[0007] It is an object of the present disclosure to provide asolar cellwith Sn2S3 layer between back contact and CZTSSe layer to reduce chances of recombination at rear/back side of the solar cell.
[0008] It is an object of the present disclosure to provide a solar cell that facilitates in enhancing power conversion efficiency with help of Sn2S3 layer used as a Back surface field (BSF) layer, which iscost efficient, having high carrier concentration.
[0009] It is an object of the present disclosure to provide asolar cell that has increased electron collection capability as band of the solar cell (at CZTSSe/BSF interface) is towards upwards.
[0010] It is an object of the present disclosure to provide asolar cell where there is less chance that electrons move towardsCZTSSe/BSF interface and recombine, thereby increasing collection capability and efficiencyof the solar cell.
[0011] It is an object of the present disclosure to provide asolar cell where Sn2S3 layer more efficiently preventcarriers to recombine and hence act as a better BSF.

SUMMARY
[0012] Thepresent disclosure relates generally to field of electrical and electronics device. More particularly, the present disclosure provides a CZTSSe based solar cell to increase power conversion efficiency with Sn2S3 layer.
[0013] An aspect of the present disclosure pertains to a CZTSSe based solar cell. The solar cell may include a tin sulphide (Sn2S3) layer, CZTSSe layer, a cadmium sulphide (CdS) layer, a zinc oxide (i-ZnO) layer, and a zinc oxide (ZnO) layer. The (Sn2S3) layer may be embedded as a Back Surface Field (BSF) for a CZTSSe layer, where the CZTSSe layer may be fabricated above the (Sn2S3) layer (102), where the CZTSSelayermay act as an as an absorber layer and the Sn2S3 layer act as the (BSF). The cadmium sulphide (CdS) (106) layer may be fabricated between the CZTSSe layer and a zinc oxide (i-ZnO) layer. The zinc oxide (i-ZnO) layer may be fabricated above the CdS layer. The Zinc oxide (ZnO) layer may be fabricated above the i-ZnO layer, where an interface of the CZTSSe layer and the Sn2S3 layer may facilitate restricting flow of a set of electrons and wherethe set of electrons may be directed towards the CZTSSe layer, and where theSn2S3 layer may facilitateincreasing power conversionefficiency of theCZTSSebased solar cell.
[0014] In an aspect, electric field generated at the interface of the CZTSSe layer and the Sn2S3 layer may facilitatein preventing movement of the set of electrons towards a rear end of theCZTSSebased solar cell.
[0015] In an aspect, at the interface of the CZTSSe layer and the Sn2S3 layer,a bandmay move in a pre-determined direction and facilitates in preventing the set of electrons to move towards a back side of the CZTSSebased solar cell.
[0016] In an aspect, the prevention of the set of electrons to move towards the back side may enable in avoiding back surface recombination and increasing collection capability of a set of carriers and may facilitate enhancing power conversion efficiency of the CZTSSe based solar cell.
[0017] In an aspect, the Sn2S3 layer as a BSF layer may have highly tolerance for aninterface defect density valuewithin a pre-defined range from5x1010 cm-2 to 5x1013 cm-2.
[0018] In an aspect,Sn2S3 layer (102) as a BSF layer without dependency on acceptor doping of theBSF layer from doping value within a pre-defined range from1x1016 cm-3 to 3x1018 cm-3.

BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0020] The diagrams are for illustration only, which thus is not a limitation of the present disclosure, and wherein:
[0021] FIG. 1 illustrates an exemplary view of proposed CZTSSe based solar cell, in accordance with an embodiment of the present disclosure.
[0022] FIG. 2 illustrates exemplaryenergy band diagram of CZTSSe with tin sulphide (Sn2S3) as a Back surface field (BSF), in accordance with an embodiment of the present disclosure.
[0023] FIG. 3 illustrates exemplaryEnergy band diagram of CZTSSe solar cell (a) without BSF (b) with SnS as a BSF (c) with Sn2S3 as a BSF, in accordance with an embodiment of the present disclosure.
[0024] FIG. 4 illustrates exemplary current density curve of CZTSSe solar cell (a) without BSF (b) with SnS as a BSF (c) with Sn2S3 as a BSF, in accordance with an embodiment of the present disclosure.
[0025] FIG. 5 illustrates exemplary curves for Impact of interface defects from 5x1010 cm-2 to 5x1013 cm-2 on current density curve for (a) with SnS as a BSF device (b) the proposed solar cell (with Sn2S3), in accordance with an embodiment of the present disclosure.
[0026] FIG. 6 illustrates exemplary curves for Impact of BSF layer doping on band diagram ofSnS as a BSF device (b) the proposed solar cell (with Sn2S3),in accordance with an embodiment of the present disclosure.
[0027] FIG. 7 illustrates exemplary curves for Impact of interface defects from 5x1010 cm-2 to 5x1013 cm-2 on (a) with SnS as a BSF (b) the solar cell (with Sn2S3),in accordance with an embodiment of the present disclosure.

DETAIL DESCRIPTION
[0028] In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without some of these specific details.
[0029] The present disclosure relates generally to field of electrical and electronics device. More particularly, the present disclosure provides a CZTSSe based solar cell to increase power conversion efficiency with Sn2S3 layer.
[0030] FIG. 1 illustrates an exemplary view of proposed CZTSSe based solar cell, in accordance with an embodiment of the present disclosure.
[0031] As illustrated in FIG. 1, the proposed CZTSSe based solar cell (100) (interchangeable referred to as solar cell (100), herein) can include a tin sulphide (Sn2S3) (102) layer embedded as a Back Surface Field (BSF) for a CZTSSe layer (104), where the CZTSSe layer(104) can be fabricated above the (Sn2S3) layer (102). In an embodiment, the CZTSSe layer (104) can act as an as an absorber layer and the Sn2S3 layer (102) act as the (BSF). The solar cell (100) can include a cadmium sulphide (CdS) (106) layer fabricated between the CZTSSe layer (104) and a zinc oxide (i-ZnO) layer (108). The zinc oxide (i-ZnO) layer (108) can befabricated above the CdS layer (106).
[0032] In an embodiment, the solar cell (100) can include a zinc oxide (ZnO) layer (110) fabricated above the i-ZnO layer (108), where an interface of the CZTSSe layer (104) and the Sn2S3 layer (102) can facilitate restricting flow of a set of electrons and where the set of electrons can be directed towards theCZTSSe layer (104). In another embodiment, theSn2S3 layer (102) can facilitate increasing power conversion efficiency of the CZTSSe based solar cell (100).
[0033] In an embodiment, electric field generated at the interface of the CZTSSe layer (104) and the Sn2S3 layer (102) can facilitate in preventing movement of the set of electrons towards a rear end of the CZTSSe based solar cell (100). In another embodiment, at the interface of the CZTSSe layer (104) and the Sn2S3 layer (102), a bandcan moves in a pre-determined direction, where the pre-determined direction can be upward, and facilitates in preventing the set of electrons to move towards a back side of the CZTSSe based solar cell (100).
[0034] In an embodiment, the prevention of the set of electrons to move towards the back side can enablein avoiding back surface recombination and increasing collection capability of a set of carriers and facilitates enhancing power conversion efficiency of the CZTSSe based solar cell (100). In another embodiment,the Sn2S3layer (102) as a BSF layer can have highly tolerance for an interface defect density value within a pre-defined range from5x1010 cm-2 to 5x1013 cm-2. In yet another embodiment, theSn2S3 layer (102) as a BSF layer without dependency on acceptor doping of theBSF layer from doping value within a pre-defined range from1x1016 cm-3 to 3x1018 cm-3.
[0035] In an embodiment, the device (100) can be structure of CZTSSe layer (104) with Sn2S3 layer (102) as a BSF layer. The Sn2S3 layer (102) can be introduced between back contact and the CZTSSe layer (104). At interface of the CZTSSe layer (104)/ Sn2S3,layer (102), band can be upward and prevent set of electrons to move towards back side. Thus, there are no back surface recombination, and increases collection of carriers and facilitates increasing power conversion efficiency of the solar cell relates to a CZTSSe based solar cell with a back surface layer to increase efficiency of the solar cells.
[0036] In an embodiment, the solar cell (100) can include plurality of layers including ZnO layer (110), i-ZnO layer (108), CdS layer (106), and CTZSSe layer (104). A layer of Sn2S3 layer (102) can be fabricated as a back surface layer in between the CZTSSe layer (104) and back contact. At interface of the CZTSSe layer (104) /Sn2S3 layer (102), band can move upward that prevents the set ofelectrons to move towards the back side, therefore there is no back surface recombination, consequently collection capability of the set of carriers is increased, and thus power conversion efficiency of the solar cell (100) can be enhanced.
[0037] In an embodiment, while using Sn2S3 layer (102) as a BSF layer ,the bands at the interface of the CZTSSe layer (104)/Sn2S3 layer (102) can acts as a barrier for the set of electrons, thus electrons come back to active layer (CZTSSe). In another embodiment, while using Sn2S3 layer (102) as the back surface layer, if defects occur during fabrication, performance of the solar cell (100) will not decrease, as interface field is sufficient to prevent motion of minority set of carriers electrons and negligible performance degradation can be observed.
[0038] In an embodiment, while using Sn2S3 as the back surface layer, the bands at CZTSSe/Sn2S3 interface for the lower doping level may be higher enough to prevent the carriers to move into back surface. A CZTSSe based solar cell comprising a plurality of layers, wherein Sn2S3 is fabricated as aback surface layer in between a CZTSSe layer and a back contact, the Sn2S3 layer is adapted to enhance efficiency of the solar cell.
[0039] Table I: Electrical parameters of all the layers

[0040] In an illustrative embodiment, the proposed device (100) can be compared with an existing devicewith Sn2S3 layer as a BSF with existing one. The device (100) can be compared with an existing devicewithout BSF, here there is no BSF layer present, and the set of electrons are free to move towards backside and recombine. In another illustrative embodiment, the device (100) can be compared with an existing device where anSnSlayer can act as a BSF layer, where the SnS layer can be used to prevent movement of the set of electrons towards the backside but due to downward banding at CZTSSe layer /SnS layer interface, the set of electrons can go at the interface and recombine. In yet another illustrative embodiment, the device (100), where the Sn2S3 layer can act as a BSF layer, andthe bands at the interface of CZTSSe/Sn2S3 layer is upwards, where the band can act as a barrier for the set of electrons. The set of electrons will not go there and come back to an active layer (CZTSSe).
[0041] FIG. 2 illustrates exemplary energy band diagram of CZTSSe with tin sulphide (Sn2S3) as a Back surface field (BSF), in accordance with an embodiment of the present disclosure.
[0042] FIG. 3 illustrates exemplary Energy band diagram of CZTSSe solar cell (a) without BSF (b) with SnS as a BSF (c) with Sn2S3 as a BSF, in accordance with an embodiment of the present disclosure.
[0043] In an embodiment, FIG. 3 illustratesenergy band diagram of CZTSSe solar cell (a) without BSF (b) with SnS as a BSF (c) with Sn2S3 as a BSF.
[0044] TABLE II PHOTOVOLTAIC PARAMETERS OF CZTSSE BASED SOLAR CELL WITHOUT BSF, WITH SNS BSF AND WITH SN2S3 BSF
Parameters D0 D1 D2
Voc (V) 0.52 0.59 0.59
JSC (mA/cm2) 34.44 37.74 37.68
FF (%) 69.51 73.36 76.46
PCE (%) 12.57 16.34 17.04
[0045] FIG. 4 illustrates exemplary current density curve of CZTSSe solar cell (a) without BSF (b) with SnS as a BSF (c) with Sn2S3 as a BSF, in accordance with an embodiment of the present disclosure.
[0046] In an embodiment, FIG. 4 illustrates current density curve of curve of CZTSSe solar cell (a) without BSF (b) with SnS as a BSF (c) with Sn2S3 as a BSF, where the Sn2S3 layer (102) more efficiently can prevent the set of carriers to recombine and hence act as a better BSF.
[0047] FIG. 5 illustrates exemplary curves for Impact of interface defects from 5x1010 cm-2 to 5x1013 cm-2 on current density curve for (a) with SnS as a BSF device (b) the proposed solar cell (with Sn2S3), in accordance with an embodiment of the present disclosure.
[0048] As illustrated in FIG. 5, withSnS as BSF layer device performance can bedegraded when one or more defects are increased from 5x1010 cm-2 to 5x1013 cm-2. This is due to enhanced set of carriers recombintaion at back surface of existing device and electric field at interface is not sufficient to prevent recombination. In an embodiment, the solar cell (100) with Sn2S3 (102) as BSF layer if defect will occur during fabrication of the solar cell (100), performance of the solar cell (100) does not decrease as interface field can be sufficiently large to prevent motion of minority carriers electrons and hence negligible performnace degradtion can be obsered even at interface defect density of 5x1013 cm-3. In another embodiment, the solar cell (100) can show high tolerance for the interface defect density value from 5x1010 cm-2 to 5x1013 cm-2.
[0049] FIG. 6 illustrates exemplary curves for Impact of BSF layer doping on band diagram of SnS as a BSF device (b) the proposed solar cell (with Sn2S3), in accordance with an embodiment of the present disclosure.
[0050] In an embodiment, FIG. 6 illustrates Energy Band Diagram (EBD) for the existing device with SnS as BSF illustrate that the band at CZTSSe layer (104)/SnSlayer (102) interface for higher doping value of SnS can be shifted upward, where magnified view can also be shown in inset of Fig. 6 (a).Upward movement at higher SnS doping can prevent more set of carriers to move into back side of the solar cell (100) than the device for the lower SnS doping (shown in Fig. 6 (a)). In another embodiment, the solar cell (100) with Sn2S3layer (102) as a BSF,the bands at CZTSSe layer (104)/Sn2S3layer (102) interface for lower doping level are also higher enough to prevent the set ofcarriers to move into back surface clearly shown in the inset of Fig. 6 (b).
[0051] FIG. 7 illustrates exemplary curves for Impact of interface defects from 5x1010 cm-2 to 5x1013 cm-2 on (a) with SnS as a BSF (b) the solar cell (with Sn2S3), in accordance with an embodiment of the present disclosure.
[0052] In an embodiment, impact of SnS and Sn2S3 dopingJ-V curves for existing device with SnS as BSF and with the solar cell (100) with the Sn2S3 layer (102) as a BSF can be shown in Fig. 7 (a-b). Result shows that performance of the existing device with SnS as BSF can depend on doping value of BSF layer (SnS), as doping value can be decreased and performance also decreases. While the solar cell (100) does not have dependency on acceptor doping of BSF layer and also shows.The proposed device also showed not dependency on the acceptor doping of BSF layer from doping value 1x1016 to 3x1018.
[0053] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE PRESENT DISCLOSURE
[0054] The present disclosure providesasolar cellwith Sn2S3 layer between back contact and CZTSSe layer to reduce chances of recombination at rear/back side of the solar cell.
[0055] The present disclosure provides a solar cell that facilitates in enhancing power conversion efficiency with help of Sn2S3 layer used as a Back surface field (BSF) layer, which is cost efficient, having high carrier concentration.
[0056] The present disclosure provides a solar cell that has increased electron collection capability as band of the solar cell (at CZTSSe/BSF interface) is towards upwards.
[0057] The present disclosure provides a solar cell where there is less chance that electrons move towards CZTSSe/BSF interface and recombine, thereby increasing collection capability and efficiency of the solar cell.
[0058] The present disclosure provides a solar cell where Sn2S3 layer more efficiently prevent carriers to recombine and hence act as a better BSF.

We Claims:

1. A CZTSSe based solar cell (100) comprising:
a tin sulphide (Sn2S3) (102) layer embedded as a Back Surface Field (BSF) for a CZTSSe layer (104), wherein the CZTSSe layer(104) is fabricated above the (Sn2S3) layer (102), wherein the CZTSSelayer (104) act as an as an absorber layer and the Sn2S3layer (102) act as the(BSF);
a cadmium sulphide (CdS) (106)layer fabricated abovethe CZTSSe layer(104);
a zincoxide (i-ZnO) layer (108) fabricated above the CdS layer (106), and
a zinc oxide (ZnO) layer (110) fabricated above the i-ZnO layer (108), wherein an interface of the CZTSSe layer (104) and the Sn2S3 layer (102) facilitates restricting flow of a set of electrons and wherein the set of electrons are directed towards theCZTSSe layer (104), and wherein the Sn2S3layer (102) facilitates increasing power conversion efficiency of the CZTSSe based solar cell (100).
2. The CZTSSe based solar cell(100) as claimed in claim 1, wherein electric field generated at the interface of the CZTSSe layer (104) and the Sn2S3 layer (102) facilitates in preventing movement of the set of electrons towards a rear end of the CZTSSe based solar cell (100).
3. The CZTSSe based solar cell(100) as claimed in claim 1, wherein at the interface of the CZTSSe layer (104) and the Sn2S3 layer (102), a band moves in a pre-determined direction and facilitates in preventing the set of electrons to move towards a back side of the CZTSSe based solar cell (100).
4. The CZTSSe based solar cell (100) as claimed in claim 3, wherein the prevention of the set of electrons to move towards the back side enables in avoiding back surface recombination and increasing collection capability of a set of carriers and facilitates enhancing power conversion efficiency of the CZTSSe based solar cell (100).
5. The CZTSSe basedsolar cell as claimed in claim 1, wherein the Sn2S3layer (102) as a BSF layerhas highly tolerance for aninterface defect density valuewithin a pre-defined range from 5x1010 cm-2 to 5x1013 cm-2.
6. The CZTSSe based solar cell as claimed in claim 1, wherein Sn2S3layer (102) as a BSF layer without dependency on acceptor doping of theBSF layer from doping value within a pre-defined range from1x1016 cm-3 to 3x1018 cm-3.