(JP9511102-W)      A solar cell having at least three layers of alternate polarity material defining p-n junctions between each pair of alternate layers, at least three layers having a max. dopant concn. above 1017 atoms cm-3 and at least three layers having a thickness which is not substantially greater than a minority carrier diffusion length for the dopant concn. of the material in the respective layer. Also claimed is a method of forming a thin film solar cell comprising the steps of:- 1) forming onto a substrate a series of alternatively doped thin layers of semiconductor material to form a series of rectifying junctions therebetween the max. dopant concn. of at least 3 layers being greater than 1017 atoms cm-3, and each layer having thickness not substantially greater than the minority carrier diffusion length of the respective doped material, 2) forming sequentially at least two sets of grooves in the series of layers to expose some or all of the doped layers, 3) forming in at least one of the grooves a p-type surface region over the entire surface of the groove or grooves, 4) forming in at least one other of the grooves an n-type surface region over the entire surface of the respective groove or grooves, 5) forming a metal contact in each of the grooves respectively to make contact with the p-type and n-type surface regions.    ADVANTAGE -   Low cost cells are produced from low quality material by employing very high doping levels.    (US5797998-A)      A solar cell having at least three layers of alternate polarity material defining p-n junctions between each pair of alternate layers, at least three layers having a max. dopant concn. above 1017 atoms cm-3 and at least three layers having a thickness which is not substantially greater than a minority carrier diffusion length for the dopant concn. of the material in the respective layer. Also claimed is a method of forming a thin film solar cell comprising the steps of:- 1) forming onto a substrate a series of alternatively doped thin layers of semiconductor material to form a series of rectifying junctions therebetween the max. dopant concn. of at least 3 layers being greater than 1017 atoms cm-3, and each layer having thickness not substantially greater than the minority carrier diffusion length of the respective doped material, 2) forming sequentially at least two sets of grooves in the series of layers to expose some or all of the doped layers, 3) forming in at least one of the grooves a p-type surface region over the entire surface of the groove or grooves, 4) forming in at least one other of the grooves an n-type surface region over the entire surface of the respective groove or grooves, 5) forming a metal contact in each of the grooves respectively to make contact with the p-type and n-type surface regions.    ADVANTAGE -   Low cost cells are produced from low quality material by employing very high doping levels.    (CN1145139-A)      A solar cell having at least three layers of alternate polarity material defining p-n junctions between each pair of alternate layers, at least three layers having a max. dopant concn. above 1017 atoms cm-3 and at least three layers having a thickness which is not substantially greater than a minority carrier diffusion length for the dopant concn. of the material in the respective layer. Also claimed is a method of forming a thin film solar cell comprising the steps of:- 1) forming onto a substrate a series of alternatively doped thin layers of semiconductor material to form a series of rectifying junctions therebetween the max. dopant concn. of at least 3 layers being greater than 1017 atoms cm-3, and each layer having thickness not substantially greater than the minority carrier diffusion length of the respective doped material, 2) forming sequentially at least two sets of grooves in the series of layers to expose some or all of the doped layers, 3) forming in at least one of the grooves a p-type surface region over the entire surface of the groove or grooves, 4) forming in at least one other of the grooves an n-type surface region over the entire surface of the respective groove or grooves, 5) forming a metal contact in each of the grooves respectively to make contact with the p-type and n-type surface regions.    ADVANTAGE -   Low cost cells are produced from low quality material by employing very high doping levels.